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[Xen-devel] [PATCH] xenpaging: handle GNTST_eagain in kernel drivers



Handle GNTST_eagain status from GNTTABOP_map_grant_ref and GNTTABOP_copy
operations properly to allow usage of xenpaging without causing crashes or data
corruption.

Remove the existing retry code from net_rx_action(), dispatch_rw_block_io(),
net_accel_map_grants_contig() and net_accel_map_iomem_page() and replace all
relevant HYPERVISOR_grant_table_op() calls with a retry loop.
This loop is implemented as a macro to allow different GNTTABOP_* args.
It will sleep up to 33 seconds and wait for the page to be paged in again.

All ->status checks were updated to use the GNTST_* namespace.
All return values are converted from GNTST_* namespace to 0/-EINVAL, since all
callers did not use the actual return value.

Signed-off-by: Olaf Hering <olaf@xxxxxxxxx>

---
Compiled with x86_64 and i386 configs

 drivers/xen/blkback/blkback.c              |   57 ++++++-----------------------
 drivers/xen/blkback/common.h               |    2 -
 drivers/xen/blkback/interface.c            |   22 +++++------
 drivers/xen/blktap/blktap.c                |   29 ++++++--------
 drivers/xen/blktap/interface.c             |   22 +++++------
 drivers/xen/blktap2/device.c               |   34 ++++++++---------
 drivers/xen/core/gnttab.c                  |    4 +-
 drivers/xen/gntdev/gntdev.c                |   26 ++++++-------
 drivers/xen/netback/interface.c            |   26 ++++---------
 drivers/xen/netback/netback.c              |   52 +++++++-------------------
 drivers/xen/scsiback/interface.c           |   24 +++++-------
 drivers/xen/scsiback/scsiback.c            |   16 ++------
 drivers/xen/sfc_netutil/accel_util.c       |   41 +++++---------------
 drivers/xen/tpmback/interface.c            |   22 +++++------
 drivers/xen/tpmback/tpmback.c              |   22 +++--------
 drivers/xen/usbback/interface.c            |   25 ++++--------
 drivers/xen/usbback/usbback.c              |   16 ++------
 drivers/xen/xenbus/xenbus_backend_client.c |   27 ++++++-------
 include/xen/gnttab.h                       |   38 +++++++++++++++++++
 19 files changed, 204 insertions(+), 301 deletions(-)

--- linux-2.6.18-xen.hg.orig/drivers/xen/blkback/blkback.c
+++ linux-2.6.18-xen.hg/drivers/xen/blkback/blkback.c
@@ -107,7 +107,7 @@ static inline unsigned long vaddr(pendin
 
 
 static int do_block_io_op(blkif_t *blkif);
-static int dispatch_rw_block_io(blkif_t *blkif,
+static void dispatch_rw_block_io(blkif_t *blkif,
                                 blkif_request_t *req,
                                 pending_req_t *pending_req);
 static void make_response(blkif_t *blkif, u64 id,
@@ -312,13 +312,13 @@ static int do_block_io_op(blkif_t *blkif
        blkif_request_t req;
        pending_req_t *pending_req;
        RING_IDX rc, rp;
-       int more_to_do = 0, ret;
+       int more_to_do = 0;
 
        rc = blk_rings->common.req_cons;
        rp = blk_rings->common.sring->req_prod;
        rmb(); /* Ensure we see queued requests up to 'rp'. */
 
-       while ((rc != rp) || (blkif->is_suspended_req)) {
+       while ((rc != rp)) {
 
                if (RING_REQUEST_CONS_OVERFLOW(&blk_rings->common, rc))
                        break;
@@ -335,14 +335,6 @@ static int do_block_io_op(blkif_t *blkif
                        break;
                }
 
-        /* Handle the suspended request first, if one exists */
-        if(blkif->is_suspended_req)
-        {
-            memcpy(&req, &blkif->suspended_req, sizeof(req));
-            blkif->is_suspended_req = 0;
-            goto handle_request;
-        }
-
                switch (blkif->blk_protocol) {
                case BLKIF_PROTOCOL_NATIVE:
                        memcpy(&req, RING_GET_REQUEST(&blk_rings->native, rc), 
sizeof(req));
@@ -361,19 +353,17 @@ static int do_block_io_op(blkif_t *blkif
                /* Apply all sanity checks to /private copy/ of request. */
                barrier();
 
-handle_request:
-        ret = 0;
                switch (req.operation) {
                case BLKIF_OP_READ:
                        blkif->st_rd_req++;
-                       ret = dispatch_rw_block_io(blkif, &req, pending_req); 
+                       dispatch_rw_block_io(blkif, &req, pending_req);
                        break;
                case BLKIF_OP_WRITE_BARRIER:
                        blkif->st_br_req++;
                        /* fall through */
                case BLKIF_OP_WRITE:
                        blkif->st_wr_req++;
-                       ret = dispatch_rw_block_io(blkif, &req, pending_req);
+                       dispatch_rw_block_io(blkif, &req, pending_req);
                        break;
                default:
                        /* A good sign something is wrong: sleep for a while to
@@ -386,17 +376,6 @@ handle_request:
                        free_req(pending_req);
                        break;
                }
-        BUG_ON(ret != 0 && ret != -EAGAIN);
-        /* If we can't handle the request at the moment, save it, and break the
-         * loop */ 
-        if(ret == -EAGAIN)
-        {
-            memcpy(&blkif->suspended_req, &req, sizeof(req));
-            blkif->is_suspended_req = 1;
-            /* Return "no more work pending", restart will be handled 'out of
-             * band' */
-            return 0;
-        }
 
                /* Yield point for this unbounded loop. */
                cond_resched();
@@ -405,7 +384,7 @@ handle_request:
        return more_to_do;
 }
 
-static int dispatch_rw_block_io(blkif_t *blkif,
+static void dispatch_rw_block_io(blkif_t *blkif,
                                 blkif_request_t *req,
                                 pending_req_t *pending_req)
 {
@@ -474,15 +453,13 @@ static int dispatch_rw_block_io(blkif_t
        ret = HYPERVISOR_grant_table_op(GNTTABOP_map_grant_ref, map, nseg);
        BUG_ON(ret);
 
-#define GENERAL_ERR   (1<<0)
-#define EAGAIN_ERR    (1<<1)
        for (i = 0; i < nseg; i++) {
-               if (unlikely(map[i].status != 0)) {
+               if (unlikely(map[i].status == GNTST_eagain))
+                       
gnttab_check_GNTST_eagain_do_while(GNTTABOP_map_grant_ref, &map[i])
+               if (unlikely(map[i].status != GNTST_okay)) {
                        DPRINTK("invalid buffer -- could not remap it\n");
                        map[i].handle = BLKBACK_INVALID_HANDLE;
-                       ret |= GENERAL_ERR;
-            if(map[i].status == GNTST_eagain)
-                           ret |= EAGAIN_ERR;
+                       ret = 1;
                } else {
                        blkback_pagemap_set(vaddr_pagenr(pending_req, i),
                                            pending_page(pending_req, i),
@@ -502,14 +479,6 @@ static int dispatch_rw_block_io(blkif_t
                        (req->seg[i].first_sect << 9);
        }
 
-    /* If any of grant maps failed with GNTST_eagain, suspend and retry later 
*/
-    if(ret & EAGAIN_ERR)
-    {
-        fast_flush_area(pending_req);
-        free_req(pending_req);
-        return -EAGAIN;
-    }
-
        if (ret)
                goto fail_flush;
 
@@ -575,7 +544,7 @@ static int dispatch_rw_block_io(blkif_t
        else if (operation == WRITE || operation == WRITE_BARRIER)
                blkif->st_wr_sect += preq.nr_sects;
 
-       return 0;
+       return;
 
  fail_flush:
        fast_flush_area(pending_req);
@@ -583,7 +552,7 @@ static int dispatch_rw_block_io(blkif_t
        make_response(blkif, req->id, req->operation, BLKIF_RSP_ERROR);
        free_req(pending_req);
        msleep(1); /* back off a bit */
-       return 0;
+       return;
 
  fail_put_bio:
        __end_block_io_op(pending_req, -EINVAL);
@@ -591,7 +560,7 @@ static int dispatch_rw_block_io(blkif_t
                bio_put(bio);
        unplug_queue(blkif);
        msleep(1); /* back off a bit */
-       return 0;
+       return;
 }
 
 
--- linux-2.6.18-xen.hg.orig/drivers/xen/blkback/common.h
+++ linux-2.6.18-xen.hg/drivers/xen/blkback/common.h
@@ -83,8 +83,6 @@ typedef struct blkif_st {
        struct task_struct  *xenblkd;
        unsigned int        waiting_reqs;
        request_queue_t     *plug;
-    int                 is_suspended_req;
-    blkif_request_t     suspended_req;
 
        /* statistics */
        unsigned long       st_print;
--- linux-2.6.18-xen.hg.orig/drivers/xen/blkback/interface.c
+++ linux-2.6.18-xen.hg/drivers/xen/blkback/interface.c
@@ -59,25 +59,23 @@ blkif_t *blkif_alloc(domid_t domid)
 static int map_frontend_page(blkif_t *blkif, unsigned long shared_page)
 {
        struct gnttab_map_grant_ref op;
+       int ret;
 
        gnttab_set_map_op(&op, (unsigned long)blkif->blk_ring_area->addr,
                          GNTMAP_host_map, shared_page, blkif->domid);
 
-    do {
-           if (HYPERVISOR_grant_table_op(GNTTABOP_map_grant_ref, &op, 1))
-                   BUG();
-        msleep(100);
-    } while(op.status == GNTST_eagain);
+       gnttab_check_GNTST_eagain_do_while(GNTTABOP_map_grant_ref, &op);
 
-       if (op.status) {
-               DPRINTK(" Grant table operation failure !\n");
-               return op.status;
+       if (op.status == GNTST_okay) {
+               blkif->shmem_ref = shared_page;
+               blkif->shmem_handle = op.handle;
+               ret = 0;
+       } else {
+               DPRINTK(" Grant table operation failure %d!\n", (int)op.status);
+               ret = -EINVAL;
        }
 
-       blkif->shmem_ref = shared_page;
-       blkif->shmem_handle = op.handle;
-
-       return 0;
+       return ret;
 }
 
 static void unmap_frontend_page(blkif_t *blkif)
--- linux-2.6.18-xen.hg.orig/drivers/xen/blktap/blktap.c
+++ linux-2.6.18-xen.hg/drivers/xen/blktap/blktap.c
@@ -1526,19 +1526,17 @@ static void dispatch_rw_block_io(blkif_t
 
                        uvaddr = MMAP_VADDR(info->user_vstart, usr_idx, i/2);
 
-                       if (unlikely(map[i].status != 0)) {
-                               WPRINTK("invalid kernel buffer -- "
-                                       "could not remap it\n");
-                if(map[i].status == GNTST_eagain)
-                    WPRINTK("grant GNTST_eagain: please use blktap2\n");
-                               ret |= 1;
+                       gnttab_check_GNTST_eagain_while(GNTTABOP_map_grant_ref, 
&map[i]);
+
+                       if (unlikely(map[i].status != GNTST_okay)) {
+                               WPRINTK("invalid kernel buffer -- could not 
remap it\n");
+                               ret = 1;
                                map[i].handle = INVALID_GRANT_HANDLE;
                        }
 
-                       if (unlikely(map[i+1].status != 0)) {
-                               WPRINTK("invalid user buffer -- "
-                                       "could not remap it\n");
-                               ret |= 1;
+                       if (unlikely(map[i+1].status != GNTST_okay)) {
+                               WPRINTK("invalid kernel buffer -- could not 
remap it\n");
+                               ret = 1;
                                map[i+1].handle = INVALID_GRANT_HANDLE;
                        }
 
@@ -1565,12 +1563,11 @@ static void dispatch_rw_block_io(blkif_t
 
                        uvaddr = MMAP_VADDR(info->user_vstart, usr_idx, i);
 
-                       if (unlikely(map[i].status != 0)) {
-                               WPRINTK("invalid kernel buffer -- "
-                                       "could not remap it\n");
-                if(map[i].status == GNTST_eagain)
-                    WPRINTK("grant GNTST_eagain: please use blktap2\n");
-                               ret |= 1;
+                       gnttab_check_GNTST_eagain_while(GNTTABOP_map_grant_ref, 
&map[i]);
+
+                       if (unlikely(map[i].status != GNTST_okay)) {
+                               WPRINTK("invalid kernel buffer -- could not 
remap it\n");
+                               ret = 1;
                                map[i].handle = INVALID_GRANT_HANDLE;
                        }
 
--- linux-2.6.18-xen.hg.orig/drivers/xen/blktap/interface.c
+++ linux-2.6.18-xen.hg/drivers/xen/blktap/interface.c
@@ -59,25 +59,23 @@ blkif_t *tap_alloc_blkif(domid_t domid)
 static int map_frontend_page(blkif_t *blkif, unsigned long shared_page)
 {
        struct gnttab_map_grant_ref op;
+       int ret;
 
        gnttab_set_map_op(&op, (unsigned long)blkif->blk_ring_area->addr,
                          GNTMAP_host_map, shared_page, blkif->domid);
 
-    do {
-           if (HYPERVISOR_grant_table_op(GNTTABOP_map_grant_ref, &op, 1))
-                   BUG();
-        msleep(10);
-    } while(op.status == GNTST_eagain);
+       gnttab_check_GNTST_eagain_do_while(GNTTABOP_map_grant_ref, &op);
 
-       if (op.status) {
-               DPRINTK(" Grant table operation failure !\n");
-               return op.status;
+       if (op.status == GNTST_okay) {
+               blkif->shmem_ref = shared_page;
+               blkif->shmem_handle = op.handle;
+               ret = 0;
+       } else {
+               DPRINTK("Grant table operation failure %d!\n", (int)op.status);
+               ret = -EINVAL;
        }
 
-       blkif->shmem_ref = shared_page;
-       blkif->shmem_handle = op.handle;
-
-       return 0;
+       return ret;
 }
 
 static void unmap_frontend_page(blkif_t *blkif)
--- linux-2.6.18-xen.hg.orig/drivers/xen/blktap2/device.c
+++ linux-2.6.18-xen.hg/drivers/xen/blktap2/device.c
@@ -505,10 +505,10 @@ blktap_map_foreign(struct blktap *tap,
 
                uvaddr = MMAP_VADDR(ring->user_vstart, usr_idx, i);
 
-               if (unlikely(table->grants[grant].status)) {
+               if (unlikely(table->grants[grant].status != GNTST_okay)) {
                        BTERR("invalid kernel buffer: could not remap it\n");
-            /* This should never happen: blkback should handle eagain first */
-            BUG_ON(table->grants[grant].status == GNTST_eagain);
+                       /* This should never happen: blkback should handle 
eagain first */
+                       BUG_ON(table->grants[grant].status == GNTST_eagain);
                        err |= 1;
                        table->grants[grant].handle = INVALID_GRANT_HANDLE;
                }
@@ -517,19 +517,18 @@ blktap_map_foreign(struct blktap *tap,
                foreign_mfn = table->grants[grant].dev_bus_addr >> PAGE_SHIFT;
                grant++;
 
-               if (xen_feature(XENFEAT_auto_translated_physmap))
-                       goto done;
-
-               if (unlikely(table->grants[grant].status)) {
-                       BTERR("invalid user buffer: could not remap it\n");
-                       err |= 1;
+               if (!xen_feature(XENFEAT_auto_translated_physmap)) {
+                       if (unlikely(table->grants[grant].status != 
GNTST_okay)) {
+                               /* This should never happen: blkback should 
handle eagain first */
+                               WARN_ON(table->grants[grant].status == 
GNTST_eagain);
+                               BTERR("invalid user buffer: could not remap 
it\n");
+                               err |= 1;
+                       }
                        table->grants[grant].handle = INVALID_GRANT_HANDLE;
+                       request->handles[i].user = table->grants[grant].handle;
+                       grant++;
                }
 
-               request->handles[i].user = table->grants[grant].handle;
-               grant++;
-
-       done:
                if (err)
                        continue;
 
@@ -602,11 +601,10 @@ blktap_map(struct blktap *tap,
                set_page_private(tap_page, page_private(page));
                SetPageBlkback(tap_page);
 
-               err = HYPERVISOR_grant_table_op(GNTTABOP_map_grant_ref,
-                                               &map, 1);
-               BUG_ON(err);
-        /* We are not expecting the grant op to fail */
-        BUG_ON(map.status != GNTST_okay);
+               gnttab_check_GNTST_eagain_do_while(GNTTABOP_map_grant_ref, 
&map);
+
+               /* We are not expecting the grant op to fail */
+               BUG_ON(map.status != GNTST_okay);
 
                err = vm_insert_page(ring->vma, uvaddr, tap_page);
                if (err) {
--- linux-2.6.18-xen.hg.orig/drivers/xen/core/gnttab.c
+++ linux-2.6.18-xen.hg/drivers/xen/core/gnttab.c
@@ -487,7 +487,7 @@ static int gnttab_map(unsigned int start
                return -ENOSYS;
        }
 
-       BUG_ON(rc || setup.status);
+       BUG_ON(rc || setup.status != GNTST_okay);
 
        if (shared == NULL)
                shared = arch_gnttab_alloc_shared(frames);
@@ -571,7 +571,7 @@ int gnttab_copy_grant_page(grant_ref_t r
        err = HYPERVISOR_grant_table_op(GNTTABOP_unmap_and_replace,
                                        &unmap, 1);
        BUG_ON(err);
-       BUG_ON(unmap.status);
+       BUG_ON(unmap.status != GNTST_okay);
 
        write_sequnlock(&gnttab_dma_lock);
 
--- linux-2.6.18-xen.hg.orig/drivers/xen/gntdev/gntdev.c
+++ linux-2.6.18-xen.hg/drivers/xen/gntdev/gntdev.c
@@ -578,7 +578,7 @@ static int gntdev_mmap (struct file *fli
        vma->vm_mm->context.has_foreign_mappings = 1;
 #endif
 
-    exit_ret = -ENOMEM;
+       exit_ret = -ENOMEM;
        for (i = 0; i < size; ++i) {
 
                flags = GNTMAP_host_map;
@@ -599,8 +599,8 @@ static int gntdev_mmap (struct file *fli
                ret = HYPERVISOR_grant_table_op(GNTTABOP_map_grant_ref, 
                                                &op, 1);
                BUG_ON(ret);
-               if (op.status) {
-            if(op.status != GNTST_eagain)
+               if (op.status != GNTST_okay) {
+                       if (op.status != GNTST_eagain)
                                printk(KERN_ERR "Error mapping the grant 
reference "
                                       "into the kernel (%d). domid = %d; ref = 
%d\n",
                                       op.status,
@@ -608,9 +608,9 @@ static int gntdev_mmap (struct file *fli
                                       .u.valid.domid,
                                       private_data->grants[slot_index+i]
                                       .u.valid.ref);
-            else 
-                /* Propagate eagain instead of trying to fix it up */
-                exit_ret = -EAGAIN;
+                       else
+                               /* Propagate eagain instead of trying to fix it 
up */
+                               exit_ret = -EAGAIN;
                        goto undo_map_out;
                }
 
@@ -679,7 +679,7 @@ static int gntdev_mmap (struct file *fli
                        ret = HYPERVISOR_grant_table_op(GNTTABOP_map_grant_ref,
                                                        &op, 1);
                        BUG_ON(ret);
-                       if (op.status) {
+                       if (op.status != GNTST_okay) {
                                printk(KERN_ERR "Error mapping the grant "
                                       "reference into user space (%d). domid "
                                       "= %d; ref = %d\n", op.status,
@@ -687,9 +687,9 @@ static int gntdev_mmap (struct file *fli
                                       .valid.domid,
                                       private_data->grants[slot_index+i].u
                                       .valid.ref);
-                /* This should never happen after we've mapped into 
-                 * the kernel space. */
-                BUG_ON(op.status == GNTST_eagain);
+                               /* This should never happen after we've mapped 
into
+                               * the kernel space. */
+                               BUG_ON(op.status == GNTST_eagain);
                                goto undo_map_out;
                        }
                        
@@ -713,7 +713,7 @@ static int gntdev_mmap (struct file *fli
                }
 
        }
-    exit_ret = 0;
+       exit_ret = 0;
 
        up_write(&private_data->grants_sem);
        return exit_ret;
@@ -785,7 +785,7 @@ static pte_t gntdev_clear_pte(struct vm_
                        ret = HYPERVISOR_grant_table_op(
                                GNTTABOP_unmap_grant_ref, &op, 1);
                        BUG_ON(ret);
-                       if (op.status)
+                       if (op.status != GNTST_okay)
                                printk("User unmap grant status = %d\n", 
                                       op.status);
                } else {
@@ -802,7 +802,7 @@ static pte_t gntdev_clear_pte(struct vm_
                ret = HYPERVISOR_grant_table_op(GNTTABOP_unmap_grant_ref, 
                                                &op, 1);
                BUG_ON(ret);
-               if (op.status)
+               if (op.status != GNTST_okay)
                        printk("Kernel unmap grant status = %d\n", op.status);
 
 
--- linux-2.6.18-xen.hg.orig/drivers/xen/netback/interface.c
+++ linux-2.6.18-xen.hg/drivers/xen/netback/interface.c
@@ -251,15 +251,11 @@ static int map_frontend_pages(
 
        gnttab_set_map_op(&op, (unsigned long)netif->tx_comms_area->addr,
                          GNTMAP_host_map, tx_ring_ref, netif->domid);
-    do {
-               if (HYPERVISOR_grant_table_op(GNTTABOP_map_grant_ref, &op, 1))
-                       BUG();
-        msleep(10);
-    } while(op.status == GNTST_eagain);
-
-       if (op.status) { 
-               DPRINTK(" Gnttab failure mapping tx_ring_ref!\n");
-               return op.status;
+       gnttab_check_GNTST_eagain_do_while(GNTTABOP_map_grant_ref, &op);
+
+       if (op.status != GNTST_okay) {
+               DPRINTK(" Gnttab failure mapping tx_ring_ref %d!\n", 
(int)op.status);
+               return -EINVAL;
        }
 
        netif->tx_shmem_ref    = tx_ring_ref;
@@ -267,13 +263,9 @@ static int map_frontend_pages(
 
        gnttab_set_map_op(&op, (unsigned long)netif->rx_comms_area->addr,
                          GNTMAP_host_map, rx_ring_ref, netif->domid);
-    do {
-           if (HYPERVISOR_grant_table_op(GNTTABOP_map_grant_ref, &op, 1))
-                   BUG();
-        msleep(10);
-    } while(op.status == GNTST_eagain);
+       gnttab_check_GNTST_eagain_do_while(GNTTABOP_map_grant_ref, &op);
 
-       if (op.status) {
+       if (op.status != GNTST_okay) {
                struct gnttab_unmap_grant_ref unop;
 
                gnttab_set_unmap_op(&unop,
@@ -281,8 +273,8 @@ static int map_frontend_pages(
                                    GNTMAP_host_map, netif->tx_shmem_handle);
                VOID(HYPERVISOR_grant_table_op(GNTTABOP_unmap_grant_ref,
                                               &unop, 1));
-               DPRINTK(" Gnttab failure mapping rx_ring_ref!\n");
-               return op.status;
+               DPRINTK(" Gnttab failure mapping rx_ring_ref %d!\n", 
(int)op.status);
+               return -EINVAL;
        }
 
        netif->rx_shmem_ref    = rx_ring_ref;
--- linux-2.6.18-xen.hg.orig/drivers/xen/netback/netback.c
+++ linux-2.6.18-xen.hg/drivers/xen/netback/netback.c
@@ -494,8 +494,7 @@ static inline void netbk_free_pages(int
    used to set up the operations on the top of
    netrx_pending_operations, which have since been done.  Check that
    they didn't give any errors and advance over them. */
-static int netbk_check_gop(int nr_frags, domid_t domid,
-                          struct netrx_pending_operations *npo, int *eagain)
+static int netbk_check_gop(int nr_frags, domid_t domid, struct 
netrx_pending_operations *npo)
 {
        multicall_entry_t *mcl;
        gnttab_transfer_t *gop;
@@ -503,17 +502,15 @@ static int netbk_check_gop(int nr_frags,
        int status = NETIF_RSP_OKAY;
        int i;
 
-    *eagain = 0;
-
        for (i = 0; i <= nr_frags; i++) {
                if (npo->meta[npo->meta_cons + i].copy) {
                        copy_op = npo->copy + npo->copy_cons++;
-                       if (copy_op->status != GNTST_okay) {
+                       if (unlikely(copy_op->status == GNTST_eagain))
+                               gnttab_check_GNTST_eagain_while(GNTTABOP_copy, 
copy_op);
+                       if (unlikely(copy_op->status != GNTST_okay)) {
                                DPRINTK("Bad status %d from copy to DOM%d.\n",
                                        copy_op->status, domid);
                                status = NETIF_RSP_ERROR;
-                if(copy_op->status == GNTST_eagain)
-                    *eagain = 1;
                        }
                } else {
                        if (!xen_feature(XENFEAT_auto_translated_physmap)) {
@@ -524,7 +521,7 @@ static int netbk_check_gop(int nr_frags,
 
                        gop = npo->trans + npo->trans_cons++;
                        /* Check the reassignment error code. */
-                       if (gop->status != 0) {
+                       if (unlikely(gop->status != GNTST_okay)) {
                                DPRINTK("Bad status %d from grant transfer to 
DOM%u\n",
                                        gop->status, domid);
                                /*
@@ -533,8 +530,6 @@ static int netbk_check_gop(int nr_frags,
                                 * a fatal error anyway.
                                 */
                                BUG_ON(gop->status == GNTST_bad_page);
-                if(gop->status == GNTST_eagain)
-                    *eagain = 1;
                                status = NETIF_RSP_ERROR;
                        }
                }
@@ -576,7 +571,6 @@ static void net_rx_action(unsigned long
        int nr_frags;
        int count;
        unsigned long offset;
-    int eagain;
 
        /*
         * Putting hundreds of bytes on the stack is considered rude.
@@ -680,7 +674,7 @@ static void net_rx_action(unsigned long
 
                netif = netdev_priv(skb->dev);
 
-               status = netbk_check_gop(nr_frags, netif->domid, &npo, &eagain);
+               status = netbk_check_gop(nr_frags, netif->domid, &npo);
 
                /* We can't rely on skb_release_data to release the
                   pages used by fragments for us, since it tries to
@@ -691,22 +685,14 @@ static void net_rx_action(unsigned long
                /* (Freeing the fragments is safe since we copy
                   non-linear skbs destined for flipping interfaces) */
                if (!netif->copying_receiver) {
-            /* 
-             * Cannot handle failed grant transfers at the moment (because
-             * mmu_updates likely completed)
-             */
-            BUG_ON(eagain);
                        atomic_set(&(skb_shinfo(skb)->dataref), 1);
                        skb_shinfo(skb)->frag_list = NULL;
                        skb_shinfo(skb)->nr_frags = 0;
                        netbk_free_pages(nr_frags, meta + npo.meta_cons + 1);
                }
 
-        if(!eagain)
-        {
-                   netif->stats.tx_bytes += skb->len;
-                   netif->stats.tx_packets++;
-        }
+               netif->stats.tx_bytes += skb->len;
+               netif->stats.tx_packets++;
 
                id = meta[npo.meta_cons].id;
                flags = nr_frags ? NETRXF_more_data : 0;
@@ -756,18 +742,8 @@ static void net_rx_action(unsigned long
                    !netbk_queue_full(netif))
                        netif_wake_queue(netif->dev);
 
-        if(!eagain || netbk_queue_full(netif))
-        {
-                   netif_put(netif);
-                   dev_kfree_skb(skb);
-                   netif->stats.tx_dropped += !!eagain;
-        } 
-        else
-        {
-               netif->rx_req_cons_peek += skb_shinfo(skb)->nr_frags + 1 +
-                                  !!skb_shinfo(skb)->gso_size;
-            skb_queue_head(&rx_queue, skb);
-        }
+               netif_put(netif);
+               dev_kfree_skb(skb);
 
                npo.meta_cons += nr_frags + 1;
        }
@@ -1107,7 +1083,7 @@ static int netbk_tx_check_mop(struct sk_
 
        /* Check status of header. */
        err = mop->status;
-       if (unlikely(err)) {
+       if (unlikely(err != GNTST_okay)) {
                txp = &pending_tx_info[pending_idx].req;
                make_tx_response(netif, txp, NETIF_RSP_ERROR);
                pending_ring[MASK_PEND_IDX(pending_prod++)] = pending_idx;
@@ -1128,12 +1104,12 @@ static int netbk_tx_check_mop(struct sk_
 
                /* Check error status: if okay then remember grant handle. */
                newerr = (++mop)->status;
-               if (likely(!newerr)) {
+               if (likely(newerr == GNTST_okay)) {
                        set_phys_to_machine(idx_to_pfn(pending_idx),
                                FOREIGN_FRAME(mop->dev_bus_addr>>PAGE_SHIFT));
                        grant_tx_handle[pending_idx] = mop->handle;
                        /* Had a previous error? Invalidate this fragment. */
-                       if (unlikely(err))
+                       if (unlikely(err != GNTST_okay))
                                netif_idx_release(pending_idx);
                        continue;
                }
@@ -1145,7 +1121,7 @@ static int netbk_tx_check_mop(struct sk_
                netif_put(netif);
 
                /* Not the first error? Preceding frags already invalidated. */
-               if (err)
+               if (err != GNTST_okay)
                        continue;
 
                /* First error: invalidate header and preceding fragments. */
--- linux-2.6.18-xen.hg.orig/drivers/xen/scsiback/interface.c
+++ linux-2.6.18-xen.hg/drivers/xen/scsiback/interface.c
@@ -64,27 +64,23 @@ static int map_frontend_page( struct vsc
                                unsigned long ring_ref)
 {
        struct gnttab_map_grant_ref op;
-       int err;
+       int ret;
 
        gnttab_set_map_op(&op, (unsigned long)info->ring_area->addr,
                                GNTMAP_host_map, ring_ref,
                                info->domid);
+       gnttab_check_GNTST_eagain_do_while(GNTTABOP_map_grant_ref, &op);
 
-    do {
-           err = HYPERVISOR_grant_table_op(GNTTABOP_map_grant_ref, &op, 1);
-           BUG_ON(err);
-        msleep(10);
-    } while(op.status == GNTST_eagain);
-
-       if (op.status) {
-               printk(KERN_ERR "scsiback: Grant table operation failure !\n");
-               return op.status;
+       if (op.status != GNTST_okay) {
+               printk(KERN_ERR "scsiback: Grant table operation failure 
%d!\n", (int)op.status);
+               ret = -EINVAL;
+       } else {
+               info->shmem_ref    = ring_ref;
+               info->shmem_handle = op.handle;
+               ret = 0;
        }
 
-       info->shmem_ref    = ring_ref;
-       info->shmem_handle = op.handle;
-
-       return (GNTST_okay);
+       return ret;
 }
 
 static void unmap_frontend_page(struct vscsibk_info *info)
--- linux-2.6.18-xen.hg.orig/drivers/xen/scsiback/scsiback.c
+++ linux-2.6.18-xen.hg/drivers/xen/scsiback/scsiback.c
@@ -279,22 +279,14 @@ static int scsiback_gnttab_data_map(vscs
 
                err = HYPERVISOR_grant_table_op(GNTTABOP_map_grant_ref, map, 
nr_segments);
                BUG_ON(err);
-        /* Retry maps with GNTST_eagain */
-        for(i=0; i < nr_segments; i++) {
-            while(unlikely(map[i].status == GNTST_eagain))
-            {
-                msleep(10);
-                       err = HYPERVISOR_grant_table_op(GNTTABOP_map_grant_ref, 
-                                                &map[i], 
-                                                1);
-                       BUG_ON(err);
-            }
-        }
 
                for (i = 0; i < nr_segments; i++) {
                        struct page *pg;
 
-                       if (unlikely(map[i].status != 0)) {
+                       /* Retry maps with GNTST_eagain */
+                       if (unlikely(map[i].status == GNTST_eagain))
+                               
gnttab_check_GNTST_eagain_while(GNTTABOP_map_grant_ref, &map[i]);
+                       if (unlikely(map[i].status != GNTST_okay)) {
                                printk(KERN_ERR "scsiback: invalid buffer -- 
could not remap it\n");
                                map[i].handle = SCSIBACK_INVALID_HANDLE;
                                err |= 1;
--- linux-2.6.18-xen.hg.orig/drivers/xen/sfc_netutil/accel_util.c
+++ linux-2.6.18-xen.hg/drivers/xen/sfc_netutil/accel_util.c
@@ -71,24 +71,27 @@ static int net_accel_map_grant(struct xe
                               u64 *dev_bus_addr, unsigned flags)
 {
        struct gnttab_map_grant_ref op;
+       int ret;
        
        gnttab_set_map_op(&op, (unsigned long)vaddr, flags,
                          gnt_ref, dev->otherend_id);
 
-       BUG_ON(HYPERVISOR_grant_table_op(GNTTABOP_map_grant_ref, &op, 1));
+       gnttab_check_GNTST_eagain_do_while(GNTTABOP_map_grant_ref, &op);
 
        if (op.status != GNTST_okay) {
                xenbus_dev_error
                        (dev, op.status,
                         "failed mapping in shared page %d from domain %d\n",
                         gnt_ref, dev->otherend_id);
+               ret = -EINVAL;
        } else {
                *handle = op.handle;
                if (dev_bus_addr)
                        *dev_bus_addr = op.dev_bus_addr;
+               ret = 0;
        }
 
-       return op.status;
+       return ret;
 }
 
 
@@ -112,7 +115,7 @@ static int net_accel_unmap_grant(struct
                                 "failed unmapping page at handle %d error 
%d\n",
                                 handle, op.status);
 
-       return op.status;
+       return op.status == GNTST_okay ? 0 : -EINVAL;
 }
 
 
@@ -144,7 +147,7 @@ struct net_accel_valloc_grant_mapping {
 /* Map a series of grants into a contiguous virtual area */
 static void *net_accel_map_grants_valloc(struct xenbus_device *dev, 
                                         unsigned *grants, int npages, 
-                                        unsigned flags, void **priv, int 
*errno)
+                                        unsigned flags, void **priv)
 {
        struct net_accel_valloc_grant_mapping *map;
        struct vm_struct *vm;
@@ -172,16 +175,12 @@ static void *net_accel_map_grants_valloc
 
        /* Do the actual mapping */
        addr = vm->addr;
-    if(errno != NULL) *errno = 0;
+
        for (i = 0; i < npages; i++) {
                rc = net_accel_map_grant(dev, grants[i], map->grant_handles + 
i, 
                                         addr, NULL, flags);
-               if (rc != 0)
-        {
-            if(errno != NULL) 
-                *errno = (rc == GNTST_eagain ? -EAGAIN : -EINVAL);
+               if (rc < 0)
                        goto undo;
-        }
                addr = (void*)((unsigned long)addr + PAGE_SIZE);
        }
 
@@ -230,16 +229,7 @@ void *net_accel_map_grants_contig(struct
                                unsigned *grants, int npages, 
                                void **priv)
 {
-    int errno;
-    void *ret;
-
-    do {
-           ret = net_accel_map_grants_valloc(dev, grants, npages,
-                                          GNTMAP_host_map, priv, &errno);
-        if(errno) msleep(10);
-    } while(errno == -EAGAIN);
-
-    return ret;
+    return net_accel_map_grants_valloc(dev, grants, npages, GNTMAP_host_map, 
priv);
 }
 EXPORT_SYMBOL(net_accel_map_grants_contig);
 
@@ -255,16 +245,7 @@ EXPORT_SYMBOL(net_accel_unmap_grants_con
 void *net_accel_map_iomem_page(struct xenbus_device *dev, int gnt_ref,
                             void **priv)
 {
-    int errno;
-    void *ret;
-
-       do {
-        ret = net_accel_map_grants_valloc(dev, &gnt_ref, 1, 
-                                          GNTMAP_host_map, priv, &errno);
-        if(errno) msleep(10);
-    } while(errno == -EAGAIN);
-
-    return ret;
+       return net_accel_map_grants_valloc(dev, &gnt_ref, 1, GNTMAP_host_map, 
priv);
 }
 EXPORT_SYMBOL(net_accel_map_iomem_page);
 
--- linux-2.6.18-xen.hg.orig/drivers/xen/tpmback/interface.c
+++ linux-2.6.18-xen.hg/drivers/xen/tpmback/interface.c
@@ -81,25 +81,23 @@ tpmif_t *tpmif_find(domid_t domid, struc
 static int map_frontend_page(tpmif_t *tpmif, unsigned long shared_page)
 {
        struct gnttab_map_grant_ref op;
+       int ret;
 
        gnttab_set_map_op(&op, (unsigned long)tpmif->tx_area->addr,
                          GNTMAP_host_map, shared_page, tpmif->domid);
 
-    do {
-           if (HYPERVISOR_grant_table_op(GNTTABOP_map_grant_ref, &op, 1))
-                   BUG();
-        msleep(10);
-    } while(op.status == GNTST_eagain);
+       gnttab_check_GNTST_eagain_do_while(GNTTABOP_map_grant_ref, &op);
 
-       if (op.status) {
-               DPRINTK(" Grant table operation failure !\n");
-               return op.status;
+       if (op.status != GNTST_okay) {
+               DPRINTK(" Grant table operation failure %d!\n", (int)op.status);
+               ret = -EINVAL;
+       } else {
+               tpmif->shmem_ref = shared_page;
+               tpmif->shmem_handle = op.handle;
+               ret = 0;
        }
 
-       tpmif->shmem_ref = shared_page;
-       tpmif->shmem_handle = op.handle;
-
-       return 0;
+       return ret;
 }
 
 static void unmap_frontend_page(tpmif_t *tpmif)
--- linux-2.6.18-xen.hg.orig/drivers/xen/tpmback/tpmback.c
+++ linux-2.6.18-xen.hg/drivers/xen/tpmback/tpmback.c
@@ -257,20 +257,15 @@ int _packet_write(struct packet *pak,
                gnttab_set_map_op(&map_op, idx_to_kaddr(tpmif, i),
                                  GNTMAP_host_map, tx->ref, tpmif->domid);
 
-        do {
-                   if 
(unlikely(HYPERVISOR_grant_table_op(GNTTABOP_map_grant_ref,
-                                                      &map_op, 1)))
-                           BUG();
-            if(map_op.status) msleep(10);
-               } while(map_op.status == GNTST_eagain);
+               gnttab_check_GNTST_eagain_do_while(GNTTABOP_map_grant_ref, 
&map_op);
 
-               handle = map_op.handle;
-
-               if (map_op.status) {
+               if (map_op.status != GNTST_okay) {
                        DPRINTK(" Grant table operation failure !\n");
                        return 0;
                }
 
+               handle = map_op.handle;
+
                tocopy = min_t(size_t, size - offset, PAGE_SIZE);
 
                if (copy_from_buffer((void *)(idx_to_kaddr(tpmif, i) |
@@ -397,14 +392,9 @@ static int packet_read_shmem(struct pack
                gnttab_set_map_op(&map_op, idx_to_kaddr(tpmif, i),
                                  GNTMAP_host_map, tx->ref, tpmif->domid);
 
-        do {
-                   if 
(unlikely(HYPERVISOR_grant_table_op(GNTTABOP_map_grant_ref,
-                                                      &map_op, 1)))
-                           BUG();
-            if(map_op.status) msleep(10);
-               } while(map_op.status == GNTST_eagain);
+               gnttab_check_GNTST_eagain_do_while(GNTTABOP_map_grant_ref, 
&map_op);
 
-               if (map_op.status) {
+               if (map_op.status != GNTST_okay) {
                        DPRINTK(" Grant table operation failure !\n");
                        return -EFAULT;
                }
--- linux-2.6.18-xen.hg.orig/drivers/xen/usbback/interface.c
+++ linux-2.6.18-xen.hg/drivers/xen/usbback/interface.c
@@ -110,16 +110,11 @@ static int map_frontend_pages(usbif_t *u
        gnttab_set_map_op(&op, (unsigned long)usbif->urb_ring_area->addr,
                          GNTMAP_host_map, urb_ring_ref, usbif->domid);
 
+       gnttab_check_GNTST_eagain_do_while(GNTTABOP_map_grant_ref, &op);
 
-    do {
-           if (HYPERVISOR_grant_table_op(GNTTABOP_map_grant_ref, &op, 1))
-                   BUG();
-        msleep(10);
-    } while (op.status == GNTST_eagain);
-
-       if (op.status) {
-               printk(KERN_ERR "grant table failure mapping urb_ring_ref\n");
-               return op.status;
+       if (op.status != GNTST_okay) {
+               printk(KERN_ERR "grant table failure mapping urb_ring_ref 
%d\n", (int)op.status);
+               return -EINVAL;
        }
 
        usbif->urb_shmem_ref = urb_ring_ref;
@@ -128,21 +123,17 @@ static int map_frontend_pages(usbif_t *u
        gnttab_set_map_op(&op, (unsigned long)usbif->conn_ring_area->addr,
                          GNTMAP_host_map, conn_ring_ref, usbif->domid);
 
-    do {
-           if (HYPERVISOR_grant_table_op(GNTTABOP_map_grant_ref, &op, 1))
-                   BUG();
-        msleep(10);
-    } while (op.status == GNTST_eagain);
+       gnttab_check_GNTST_eagain_do_while(GNTTABOP_map_grant_ref, &op);
 
-       if (op.status) {
+       if (op.status != GNTST_okay) {
                struct gnttab_unmap_grant_ref unop;
                gnttab_set_unmap_op(&unop,
                                (unsigned long) usbif->urb_ring_area->addr,
                                GNTMAP_host_map, usbif->urb_shmem_handle);
                VOID(HYPERVISOR_grant_table_op(GNTTABOP_unmap_grant_ref, &unop,
                                1));
-               printk(KERN_ERR "grant table failure mapping conn_ring_ref\n");
-               return op.status;
+               printk(KERN_ERR "grant table failure mapping conn_ring_ref 
%d\n", (int)op.status);
+               return -EINVAL;
        }
 
        usbif->conn_shmem_ref = conn_ring_ref;
--- linux-2.6.18-xen.hg.orig/drivers/xen/usbback/usbback.c
+++ linux-2.6.18-xen.hg/drivers/xen/usbback/usbback.c
@@ -392,19 +392,13 @@ static int usbbk_gnttab_map(usbif_t *usb
                ret = HYPERVISOR_grant_table_op(GNTTABOP_map_grant_ref,
                                        map, nr_segs);
                BUG_ON(ret);
-        /* Make sure than none of the map ops failed with GNTST_eagain */
-        for( i = 0; i < nr_segs; i++) {
-            while(map[i].status == GNTST_eagain) {
-                msleep(10);
-                       ret = HYPERVISOR_grant_table_op(
-                                GNTTABOP_map_grant_ref,
-                                               &map[i], 1);
-                       BUG_ON(ret);
-            }
-        }
 
                for (i = 0; i < nr_segs; i++) {
-                       if (unlikely(map[i].status != 0)) {
+                       /* Make sure than none of the map ops failed with 
GNTST_eagain */
+                       if (unlikely(map[i].status == GNTST_eagain))
+                               
gnttab_check_GNTST_eagain_while(GNTTABOP_map_grant_ref, &map[i]);
+
+                       if (unlikely(map[i].status != GNTST_okay)) {
                                printk(KERN_ERR "usbback: invalid buffer -- 
could not remap it\n");
                                map[i].handle = USBBACK_INVALID_HANDLE;
                                ret |= 1;
--- linux-2.6.18-xen.hg.orig/drivers/xen/xenbus/xenbus_backend_client.c
+++ linux-2.6.18-xen.hg/drivers/xen/xenbus/xenbus_backend_client.c
@@ -49,11 +49,7 @@ struct vm_struct *xenbus_map_ring_valloc
        gnttab_set_map_op(&op, (unsigned long)area->addr, GNTMAP_host_map,
                          gnt_ref, dev->otherend_id);
        
-    do {
-           if (HYPERVISOR_grant_table_op(GNTTABOP_map_grant_ref, &op, 1))
-                   BUG();
-        msleep(10);
-    } while(op.status == GNTST_eagain);
+       gnttab_check_GNTST_eagain_do_while(GNTTABOP_map_grant_ref, &op);
 
        if (op.status != GNTST_okay) {
                free_vm_area(area);
@@ -61,7 +57,7 @@ struct vm_struct *xenbus_map_ring_valloc
                                 "mapping in shared page %d from domain %d",
                                 gnt_ref, dev->otherend_id);
                BUG_ON(!IS_ERR(ERR_PTR(op.status)));
-               return ERR_PTR(op.status);
+               return ERR_PTR(-EINVAL);
        }
 
        /* Stuff the handle in an unused field */
@@ -76,23 +72,24 @@ int xenbus_map_ring(struct xenbus_device
                   grant_handle_t *handle, void *vaddr)
 {
        struct gnttab_map_grant_ref op;
+       int ret;
        
        gnttab_set_map_op(&op, (unsigned long)vaddr, GNTMAP_host_map,
                          gnt_ref, dev->otherend_id);
-    do {
-           if (HYPERVISOR_grant_table_op(GNTTABOP_map_grant_ref, &op, 1))
-                   BUG();
-        msleep(10);
-    } while(op.status == GNTST_eagain);
+
+       gnttab_check_GNTST_eagain_do_while(GNTTABOP_map_grant_ref, &op);
 
        if (op.status != GNTST_okay) {
                xenbus_dev_fatal(dev, op.status,
                                 "mapping in shared page %d from domain %d",
                                 gnt_ref, dev->otherend_id);
-       } else
+               ret = -EINVAL;
+       } else {
                *handle = op.handle;
+               ret = 0;
+       }
 
-       return op.status;
+       return ret;
 }
 EXPORT_SYMBOL_GPL(xenbus_map_ring);
 
@@ -115,7 +112,7 @@ int xenbus_unmap_ring_vfree(struct xenbu
                                 "unmapping page at handle %d error %d",
                                 (int16_t)area->phys_addr, op.status);
 
-       return op.status;
+       return op.status == GNTST_okay ? 0 : -EINVAL;
 }
 EXPORT_SYMBOL_GPL(xenbus_unmap_ring_vfree);
 
@@ -135,7 +132,7 @@ int xenbus_unmap_ring(struct xenbus_devi
                                 "unmapping page at handle %d error %d",
                                 handle, op.status);
 
-       return op.status;
+       return op.status == GNTST_okay ? 0 : -EINVAL;
 }
 EXPORT_SYMBOL_GPL(xenbus_unmap_ring);
 
--- linux-2.6.18-xen.hg.orig/include/xen/gnttab.h
+++ linux-2.6.18-xen.hg/include/xen/gnttab.h
@@ -40,6 +40,7 @@
 #include <asm/hypervisor.h>
 #include <asm/maddr.h> /* maddr_t */
 #include <linux/mm.h>
+#include <linux/delay.h>
 #include <xen/interface/grant_table.h>
 #include <xen/features.h>
 
@@ -161,4 +162,41 @@ gnttab_set_replace_op(struct gnttab_unma
        unmap->handle = handle;
 }
 
+#define gnttab_check_GNTST_eagain_while(__HCop, __HCarg_p)                     
\
+{                                                                              
\
+       u8 __hc_delay = 1;                                                      
\
+       int __ret;                                                              
\
+       while (unlikely((__HCarg_p)->status == GNTST_eagain && __hc_delay)) {   
\
+               msleep(__hc_delay++);                                           
\
+               __ret = HYPERVISOR_grant_table_op(__HCop, (__HCarg_p), 1);      
\
+               BUG_ON(__ret);                                                  
\
+       }                                                                       
\
+       if (__hc_delay == 0) {                                                  
\
+               printk(KERN_ERR "%s: %s gnt busy\n", __func__, current->comm);  
\
+               (__HCarg_p)->status = GNTST_bad_page;                           
\
+       }                                                                       
\
+       if ((__HCarg_p)->status != GNTST_okay)                                  
\
+               printk(KERN_ERR "%s: %s gnt status %x\n",                       
\
+                       __func__, current->comm, (__HCarg_p)->status);          
\
+}
+
+#define gnttab_check_GNTST_eagain_do_while(__HCop, __HCarg_p)                  
\
+{                                                                              
\
+       u8 __hc_delay = 1;                                                      
\
+       int __ret;                                                              
\
+       do {                                                                    
\
+               __ret = HYPERVISOR_grant_table_op(__HCop, (__HCarg_p), 1);      
\
+               BUG_ON(__ret);                                                  
\
+               if ((__HCarg_p)->status == GNTST_eagain)                        
\
+                       msleep(__hc_delay++);                                   
\
+       } while ((__HCarg_p)->status == GNTST_eagain && __hc_delay);            
\
+       if (__hc_delay == 0) {                                                  
\
+               printk(KERN_ERR "%s: %s gnt busy\n", __func__, current->comm);  
\
+               (__HCarg_p)->status = GNTST_bad_page;                           
\
+       }                                                                       
\
+       if ((__HCarg_p)->status != GNTST_okay)                                  
\
+               printk(KERN_ERR "%s: %s gnt status %x\n",                       
\
+                       __func__, current->comm, (__HCarg_p)->status);          
\
+}
+
 #endif /* __ASM_GNTTAB_H__ */

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