From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:53386) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1fyJQb-0006HZ-SP for qemu-devel@nongnu.org; Fri, 07 Sep 2018 12:16:19 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1fyJQU-000498-8g for qemu-devel@nongnu.org; Fri, 07 Sep 2018 12:16:11 -0400 From: Kevin Wolf Date: Fri, 7 Sep 2018 18:15:12 +0200 Message-Id: <20180907161520.26349-7-kwolf@redhat.com> In-Reply-To: <20180907161520.26349-1-kwolf@redhat.com> References: <20180907161520.26349-1-kwolf@redhat.com> Subject: [Qemu-devel] [PATCH 06/14] block: Add missing locking in bdrv_co_drain_bh_cb() List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: qemu-block@nongnu.org Cc: kwolf@redhat.com, mreitz@redhat.com, famz@redhat.com, pbonzini@redhat.com, slp@redhat.com, qemu-devel@nongnu.org bdrv_do_drained_begin/end() assume that they are called with the AioContext lock of bs held. If we call drain functions from a coroutine with the AioContext lock held, we yield and schedule a BH to move out of coroutine context. This means that the lock for the home context of the coroutine is released and must be re-acquired in the bottom half. Signed-off-by: Kevin Wolf --- include/qemu/coroutine.h | 5 +++++ block/io.c | 15 +++++++++++++++ util/qemu-coroutine.c | 5 +++++ 3 files changed, 25 insertions(+) diff --git a/include/qemu/coroutine.h b/include/qemu/coroutine.h index 6f8a487041..9801e7f5a4 100644 --- a/include/qemu/coroutine.h +++ b/include/qemu/coroutine.h @@ -90,6 +90,11 @@ void qemu_aio_coroutine_enter(AioContext *ctx, Coroutine *co); void coroutine_fn qemu_coroutine_yield(void); /** + * Get the AioContext of the given coroutine + */ +AioContext *coroutine_fn qemu_coroutine_get_aio_context(Coroutine *co); + +/** * Get the currently executing coroutine */ Coroutine *coroutine_fn qemu_coroutine_self(void); diff --git a/block/io.c b/block/io.c index 7100344c7b..914ba78f1a 100644 --- a/block/io.c +++ b/block/io.c @@ -288,6 +288,18 @@ static void bdrv_co_drain_bh_cb(void *opaque) BlockDriverState *bs = data->bs; if (bs) { + AioContext *ctx = bdrv_get_aio_context(bs); + AioContext *co_ctx = qemu_coroutine_get_aio_context(co); + + /* + * When the coroutine yielded, the lock for its home context was + * released, so we need to re-acquire it here. If it explicitly + * acquired a different context, the lock is still held and we don't + * want to lock it a second time (or AIO_WAIT_WHILE() would hang). + */ + if (ctx == co_ctx) { + aio_context_acquire(ctx); + } bdrv_dec_in_flight(bs); if (data->begin) { bdrv_do_drained_begin(bs, data->recursive, data->parent, @@ -296,6 +308,9 @@ static void bdrv_co_drain_bh_cb(void *opaque) bdrv_do_drained_end(bs, data->recursive, data->parent, data->ignore_bds_parents); } + if (ctx == co_ctx) { + aio_context_release(ctx); + } } else { assert(data->begin); bdrv_drain_all_begin(); diff --git a/util/qemu-coroutine.c b/util/qemu-coroutine.c index 1ba4191b84..2295928d33 100644 --- a/util/qemu-coroutine.c +++ b/util/qemu-coroutine.c @@ -198,3 +198,8 @@ bool qemu_coroutine_entered(Coroutine *co) { return co->caller; } + +AioContext *coroutine_fn qemu_coroutine_get_aio_context(Coroutine *co) +{ + return co->ctx; +} -- 2.13.6