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Re: [PATCH] test-bdrv-drain: fix iothread_join() hang
From: |
Stefan Hajnoczi |
Subject: |
Re: [PATCH] test-bdrv-drain: fix iothread_join() hang |
Date: |
Wed, 9 Oct 2019 15:24:24 +0100 |
User-agent: |
Mutt/1.12.1 (2019-06-15) |
On Thu, Oct 03, 2019 at 11:01:03AM +0100, Stefan Hajnoczi wrote:
> tests/test-bdrv-drain can hang in tests/iothread.c:iothread_run():
>
> while (!atomic_read(&iothread->stopping)) {
> aio_poll(iothread->ctx, true);
> }
>
> The iothread_join() function works as follows:
>
> void iothread_join(IOThread *iothread)
> {
> iothread->stopping = true;
> aio_notify(iothread->ctx);
> qemu_thread_join(&iothread->thread);
>
> If iothread_run() checks iothread->stopping before the iothread_join()
> thread sets stopping to true, then aio_notify() may be optimized away
> and iothread_run() hangs forever in aio_poll().
>
> The correct way to change iothread->stopping is from a BH that executes
> within iothread_run(). This ensures that iothread->stopping is checked
> after we set it to true.
>
> This was already fixed for ./iothread.c (note this is a different source
> file!) by commit 2362a28ea11c145e1a13ae79342d76dc118a72a6 ("iothread:
> fix iothread_stop() race condition"), but not for tests/iothread.c.
>
> Fixes: 0c330a734b51c177ab8488932ac3b0c4d63a718a
> ("aio: introduce aio_co_schedule and aio_co_wake")
> Reported-by: Dr. David Alan Gilbert <address@hidden>
> Cc: Paolo Bonzini <address@hidden>
> Signed-off-by: Stefan Hajnoczi <address@hidden>
> ---
> tests/iothread.c | 10 ++++++++--
> 1 file changed, 8 insertions(+), 2 deletions(-)
Thanks, applied to my block tree:
https://github.com/stefanha/qemu/commits/block
Stefan
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