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Re: [Qemu-block] [PATCH] blockdev: acquire AioContext in hmp_commit()

From: Denis V. Lunev
Subject: Re: [Qemu-block] [PATCH] blockdev: acquire AioContext in hmp_commit()
Date: Sun, 1 Nov 2015 20:50:36 +0300
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:38.0) Gecko/20100101 Thunderbird/38.3.0

On 10/30/2015 06:57 PM, Stefan Hajnoczi wrote:
This one slipped through.  Although we acquire AioContext when
committing all devices we don't for just a single device.

AioContext must be acquired before calling bdrv_*() functions to
synchronize access with other threads that may be using the AioContext.

Signed-off-by: Stefan Hajnoczi <address@hidden>
  blockdev.c | 12 +++++++++++-
  1 file changed, 11 insertions(+), 1 deletion(-)

diff --git a/blockdev.c b/blockdev.c
index 18712d2..d611779 100644
--- a/blockdev.c
+++ b/blockdev.c
@@ -1120,6 +1120,9 @@ void hmp_commit(Monitor *mon, const QDict *qdict)
      if (!strcmp(device, "all")) {
          ret = bdrv_commit_all();
      } else {
+        BlockDriverState *bs;
+        AioContext *aio_context;
          blk = blk_by_name(device);
          if (!blk) {
              monitor_printf(mon, "Device '%s' not found\n", device);
@@ -1129,7 +1132,14 @@ void hmp_commit(Monitor *mon, const QDict *qdict)
              monitor_printf(mon, "Device '%s' has no medium\n", device);
-        ret = bdrv_commit(blk_bs(blk));
+        bs = blk_bs(blk);
+        aio_context = bdrv_get_aio_context(bs);
+        aio_context_acquire(aio_context);
+        ret = bdrv_commit(bs);
+        aio_context_release(aio_context);
      if (ret < 0) {
          monitor_printf(mon, "'commit' error for '%s': %s\n", device,
I like it in general, but could you pls wait a bit before pushing
it up. I am working at the moment on a more generic series.
I am going to attach this patch to it to consider the situation
as a whole.

It would be much trickier than my previous one. There are
several other places discovered.


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