From: Paolo Bonzini Date: Tue, 21 Mar 2017 17:48:10 +0000 (+0100) Subject: blockjob: avoid recursive AioContext locking X-Git-Url: http://git.maquefel.me/?a=commitdiff_plain;h=d79df2a2ceb3cb0771146587e9a4bfb312577f46;p=qemu.git blockjob: avoid recursive AioContext locking Streaming or any other block job hangs when performed on a block device that has a non-default iothread. This happens because the AioContext is acquired twice by block_job_defer_to_main_loop_bh and then released only once by BDRV_POLL_WHILE. (Insert rants on recursive mutexes, which unfortunately are a temporary but necessary evil for iothreads at the moment). Luckily, the reason for the double acquisition is simple; the function acquires the AioContext for both the job iothread and the BDS iothread, in case the BDS iothread was changed while the job was running. It is therefore enough to skip the second acquisition when the two AioContexts are one and the same. Signed-off-by: Paolo Bonzini Reviewed-by: Eric Blake Reviewed-by: Jeff Cody Message-id: 1490118490-5597-1-git-send-email-pbonzini@redhat.com Signed-off-by: Jeff Cody --- diff --git a/blockjob.c b/blockjob.c index 69126af97f..2159df776b 100644 --- a/blockjob.c +++ b/blockjob.c @@ -755,12 +755,16 @@ static void block_job_defer_to_main_loop_bh(void *opaque) /* Fetch BDS AioContext again, in case it has changed */ aio_context = blk_get_aio_context(data->job->blk); - aio_context_acquire(aio_context); + if (aio_context != data->aio_context) { + aio_context_acquire(aio_context); + } data->job->deferred_to_main_loop = false; data->fn(data->job, data->opaque); - aio_context_release(aio_context); + if (aio_context != data->aio_context) { + aio_context_release(aio_context); + } aio_context_release(data->aio_context);