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[Qemu-block] [PATCH] qed: fix bdrv_qed_drain

From: Paolo Bonzini
Subject: [Qemu-block] [PATCH] qed: fix bdrv_qed_drain
Date: Tue, 16 Feb 2016 16:53:20 +0100

The current implementation of bdrv_qed_drain can cause a double
completion of a request.

The problem is that bdrv_qed_drain calls qed_plug_allocating_write_reqs
unconditionally, but this is not correct if an allocating write
is queued.  In this case, qed_unplug_allocating_write_reqs will
restart the allocating write and possibly cause it to complete.
The aiocb however is still in use for the L2/L1 table writes,
and will then be completed again as soon as the table writes
are stable.

The fix is to only call qed_plug_allocating_write_reqs and
bdrv_aio_flush (which is the same as the timer callback---the patch
makes this explicit) only if the timer was scheduled in the first
place.  This fixes qemu-iotests test 011.

Cc: address@hidden
Cc: address@hidden
Cc: Stefan Hajnoczi <address@hidden>
Signed-off-by: Paolo Bonzini <address@hidden>
 block/qed.c | 13 +++++++------
 1 file changed, 7 insertions(+), 6 deletions(-)

diff --git a/block/qed.c b/block/qed.c
index 404be1e..ebba220 100644
--- a/block/qed.c
+++ b/block/qed.c
@@ -380,12 +380,13 @@ static void bdrv_qed_drain(BlockDriverState *bs)
     BDRVQEDState *s = bs->opaque;
-    /* Cancel timer and start doing I/O that were meant to happen as if it
-     * fired, that way we get bdrv_drain() taking care of the ongoing requests
-     * correctly. */
-    qed_cancel_need_check_timer(s);
-    qed_plug_allocating_write_reqs(s);
-    bdrv_aio_flush(s->bs, qed_clear_need_check, s);
+    /* Fire the timer immediately in order to start doing I/O as soon as the
+     * header is flushed.
+     */
+    if (s->need_check_timer && timer_pending(s->need_check_timer)) {
+        qed_cancel_need_check_timer(s);
+        qed_need_check_timer_cb(s);
+    }
 static int bdrv_qed_open(BlockDriverState *bs, QDict *options, int flags,

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