[Xen-devel] [PATCH v2 2/4] xen-blkback: fix memory leaks

[Roger Pau Monne <roger.pau@xxxxxxxxxx>]

I've at least identified two possible memory leaks in blkback, both
related to the shutdown path of a VBD:

- blkback doesn't wait for any pending purge work to finish before
  cleaning the list of free_pages. The purge work will call
  put_free_pages and thus we might end up with pages being added to
  the free_pages list after we have emptied it. Fix this by making
  sure there's no pending purge work before exiting
  xen_blkif_schedule, and moving the free_page cleanup code to
  xen_blkif_free.
- blkback doesn't wait for pending requests to end before cleaning
  persistent grants and the list of free_pages. Again this can add
  pages to the free_pages list or persistent grants to the
  persistent_gnts red-black tree. Fixed by moving the persistent
  grants and free_pages cleanup code to xen_blkif_free.

Also, add some checks in xen_blkif_free to make sure we are cleaning
everything.

Signed-off-by: Roger Pau Monnà <roger.pau@xxxxxxxxxx>
Cc: Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>
Cc: David Vrabel <david.vrabel@xxxxxxxxxx>
Cc: Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx>
Cc: Matt Rushton <mrushton@xxxxxxxxxx>
Cc: Matt Wilson <msw@xxxxxxxxxx>
Cc: Ian Campbell <Ian.Campbell@xxxxxxxxxx>
---
 drivers/block/xen-blkback/blkback.c |   27 ++++++++++++++++++---------
 drivers/block/xen-blkback/common.h  |    1 +
 drivers/block/xen-blkback/xenbus.c  |   12 ++++++++++++
 3 files changed, 31 insertions(+), 9 deletions(-)

diff --git a/drivers/block/xen-blkback/blkback.c 
b/drivers/block/xen-blkback/blkback.c
index 30ef7b3..dcfe49f 100644
--- a/drivers/block/xen-blkback/blkback.c
+++ b/drivers/block/xen-blkback/blkback.c
@@ -375,7 +375,7 @@ static void purge_persistent_gnt(struct xen_blkif *blkif)
 
        pr_debug(DRV_PFX "Going to purge %u persistent grants\n", num_clean);
 
-       INIT_LIST_HEAD(&blkif->persistent_purge_list);
+       BUG_ON(!list_empty(&blkif->persistent_purge_list));
        root = &blkif->persistent_gnts;
 purge_list:
        foreach_grant_safe(persistent_gnt, n, root, node) {
@@ -625,6 +625,23 @@ purge_gnt_list:
                        print_stats(blkif);
        }
 
+       /* Drain pending purge work */
+       flush_work(&blkif->persistent_purge_work);
+
+       if (log_stats)
+               print_stats(blkif);
+
+       blkif->xenblkd = NULL;
+       xen_blkif_put(blkif);
+
+       return 0;
+}
+
+/*
+ * Remove persistent grants and empty the pool of free pages
+ */
+void xen_blkbk_free_caches(struct xen_blkif *blkif)
+{
        /* Free all persistent grant pages */
        if (!RB_EMPTY_ROOT(&blkif->persistent_gnts))
                free_persistent_gnts(blkif, &blkif->persistent_gnts,
@@ -635,14 +652,6 @@ purge_gnt_list:
 
        /* Since we are shutting down remove all pages from the buffer */
        shrink_free_pagepool(blkif, 0 /* All */);
-
-       if (log_stats)
-               print_stats(blkif);
-
-       blkif->xenblkd = NULL;
-       xen_blkif_put(blkif);
-
-       return 0;
 }
 
 /*
diff --git a/drivers/block/xen-blkback/common.h 
b/drivers/block/xen-blkback/common.h
index 8d88075..f733d76 100644
--- a/drivers/block/xen-blkback/common.h
+++ b/drivers/block/xen-blkback/common.h
@@ -376,6 +376,7 @@ int xen_blkif_xenbus_init(void);
 irqreturn_t xen_blkif_be_int(int irq, void *dev_id);
 int xen_blkif_schedule(void *arg);
 int xen_blkif_purge_persistent(void *arg);
+void xen_blkbk_free_caches(struct xen_blkif *blkif);
 
 int xen_blkbk_flush_diskcache(struct xenbus_transaction xbt,
                              struct backend_info *be, int state);
diff --git a/drivers/block/xen-blkback/xenbus.c 
b/drivers/block/xen-blkback/xenbus.c
index c2014a0..8afef67 100644
--- a/drivers/block/xen-blkback/xenbus.c
+++ b/drivers/block/xen-blkback/xenbus.c
@@ -125,6 +125,7 @@ static struct xen_blkif *xen_blkif_alloc(domid_t domid)
        blkif->persistent_gnts.rb_node = NULL;
        spin_lock_init(&blkif->free_pages_lock);
        INIT_LIST_HEAD(&blkif->free_pages);
+       INIT_LIST_HEAD(&blkif->persistent_purge_list);
        blkif->free_pages_num = 0;
        atomic_set(&blkif->persistent_gnt_in_use, 0);
 
@@ -259,6 +260,17 @@ static void xen_blkif_free(struct xen_blkif *blkif)
        if (!atomic_dec_and_test(&blkif->refcnt))
                BUG();
 
+       /* Remove all persistent grants and the cache of ballooned pages. */
+       xen_blkbk_free_caches(blkif);
+
+       /* Make sure everything is drained before shutting down */
+       BUG_ON(blkif->persistent_gnt_c != 0);
+       BUG_ON(atomic_read(&blkif->persistent_gnt_in_use) != 0);
+       BUG_ON(blkif->free_pages_num != 0);
+       BUG_ON(!list_empty(&blkif->persistent_purge_list));
+       BUG_ON(!list_empty(&blkif->free_pages));
+       BUG_ON(!RB_EMPTY_ROOT(&blkif->persistent_gnts));
+
        /* Check that there is no request in use */
        list_for_each_entry_safe(req, n, &blkif->pending_free, free_list) {
                list_del(&req->free_list);
-- 
1.7.7.5 (Apple Git-26)


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