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

[Stefan Hajnoczi]

On Sun, Nov 01, 2015 at 08:50:36PM +0300, Denis V. Lunev wrote:
> 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);
> >              return;
> >          }
> >-        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.

Sure.  We need to solve the missing AioContext acquires by hard freeze
(2015-11-12, see http://qemu-project.org/Planning/2.5).  Until then we
can discuss different solutions.

Stefan

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