[Xen-ia64-devel] [PATCH 2/4] linux/blktap: fix racy memory refernce with ring_ok

[Isaku Yamahata <yamahata@xxxxxxxxxxxxx>]

blktap: fix race memory refernce with ring_ok.

fix race memory refernce with ring_ok.
ring_ok is shared by mmapping process and blktap kernel thread.

Signed-off-by: Isaku Yamahata <yamahata@xxxxxxxxxxxxx>

diff --git a/drivers/xen/blktap/blktap.c b/drivers/xen/blktap/blktap.c
--- a/drivers/xen/blktap/blktap.c
+++ b/drivers/xen/blktap/blktap.c
@@ -617,6 +617,9 @@ static int blktap_release(struct inode *
        if (!info)
                return 0;
 
+       info->ring_ok = 0;
+       smp_wmb();
+
        info->dev_inuse = 0;
        DPRINTK("Freeing device [/dev/xen/blktap%d]\n",info->minor);
 
@@ -717,6 +720,7 @@ static int blktap_mmap(struct file *filp
 #endif
 
        info->vma = vma;
+       smp_wmb();
        info->ring_ok = 1;
        return 0;
  fail:
@@ -1390,6 +1394,7 @@ static void dispatch_rw_block_io(blkif_t
                WPRINTK("blktap: ring not ready for requests!\n");
                goto fail_response;
        }
+       smp_rmb();
 
        if (RING_FULL(&info->ufe_ring)) {
                WPRINTK("blktap: fe_ring is full, can't add "

Attachment: 1-fix-race-in-blktap.patch
Description: Text Data

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