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Re: [Qemu-block] [Qemu-devel] [PATCH v3 04/11] quorum: Fix close path

From: Max Reitz
Subject: Re: [Qemu-block] [Qemu-devel] [PATCH v3 04/11] quorum: Fix close path
Date: Wed, 25 Feb 2015 09:08:03 -0500
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:31.0) Gecko/20100101 Thunderbird/31.4.0

On 2015-02-25 at 02:12, Fam Zheng wrote:
On Tue, 02/24 10:35, Max Reitz wrote:
bdrv_unref() can lead to bdrv_close(), which in turn will result in
bdrv_drain_all(). This function will later be called blk_drain_all() and
iterate only over the BlockBackends for which blk_is_inserted() holds
true; therefore, bdrv_is_inserted() and thus quorum_is_inserted() will
probably be called.

This patch makes quorum_is_inserted() aware of the fact that some
children may have been closed already.

Signed-off-by: Max Reitz <address@hidden>
Reviewed-by: Eric Blake <address@hidden>
  block/quorum.c | 3 ++-
  1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/block/quorum.c b/block/quorum.c
index 7a75cea..5ae2398 100644
--- a/block/quorum.c
+++ b/block/quorum.c
@@ -1005,6 +1005,7 @@ static void quorum_close(BlockDriverState *bs)
for (i = 0; i < s->num_children; i++) {
+        s->bs[i] = NULL;
Is quorum_is_inserted called by bdrv_close in this bdrv_unref?

Maybe. In any case, the BDS will still be valid at that point (it's called through bdrv_drain_all() which is called from bdrv_close() before it did any modifications to the BDS; also note that this bdrv_drain_all() is actually supposed to affect the BDS being closed since bdrv_make_anon() is called only afterwards).

In effect it probably doesn't really matter whether to do the bdrv_unref() before or after s->bs[i] has been reset. If it is done before, quorum_is_inserted() will return true for the first BDS being closed (and false for all the others) which most probably won't do anything; if it is done after, quorum_is_inserted() will return false every time.


If yes, I think
unsetting s->bs[i] should happen before bdrv_unref(), so quorum_is_inserted
won't count this one again.


@@ -1070,7 +1071,7 @@ static bool quorum_is_inserted(BlockDriverState *bs)
      int i;
for (i = 0; i < s->num_children; i++) {
-        if (!bdrv_is_inserted(s->bs[i])) {
+        if (s->bs[i] && !bdrv_is_inserted(s->bs[i])) {
              return false;

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