From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:34926) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1adZWJ-00023n-7u for qemu-devel@nongnu.org; Wed, 09 Mar 2016 03:31:04 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1adZWI-0006E7-6I for qemu-devel@nongnu.org; Wed, 09 Mar 2016 03:31:03 -0500 Date: Wed, 9 Mar 2016 16:30:49 +0800 From: Fam Zheng Message-ID: <20160309083049.GI17947@ad.usersys.redhat.com> References: <1455645388-32401-1-git-send-email-pbonzini@redhat.com> <1455645388-32401-14-git-send-email-pbonzini@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1455645388-32401-14-git-send-email-pbonzini@redhat.com> Subject: Re: [Qemu-devel] [PATCH 13/16] block: only call aio_poll from iothread List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Paolo Bonzini Cc: stefanha@redhat.com, qemu-devel@nongnu.org, qemu-block@nongnu.org On Tue, 02/16 18:56, Paolo Bonzini wrote: > aio_poll is not thread safe; for example bdrv_drain can hang if > the last in-flight I/O operation is completed in the I/O thread after > the main thread has checked bs->in_flight. > > The bug remains latent as long as all of it is called within > aio_context_acquire/aio_context_release, but this will change soon. > > To fix this, if bdrv_drain is called from outside the I/O thread handle > it internally in the BDS, without involving AioContext and aio_poll. > > Signed-off-by: Paolo Bonzini > --- > block.c | 2 ++ > block/io.c | 21 ++++++++++++++++++--- > include/block/block_int.h | 5 ++++- > 3 files changed, 24 insertions(+), 4 deletions(-) > > diff --git a/block.c b/block.c > index fb02d7f..601a73f 100644 > --- a/block.c > +++ b/block.c > @@ -267,6 +267,7 @@ BlockDriverState *bdrv_new(void) > qemu_co_queue_init(&bs->throttled_reqs[1]); > bs->refcnt = 1; > bs->aio_context = qemu_get_aio_context(); > + qemu_event_init(&bs->in_flight_event, true); > > QTAILQ_INSERT_TAIL(&all_bdrv_states, bs, bs_list); > > @@ -2395,6 +2396,7 @@ static void bdrv_delete(BlockDriverState *bs) > bdrv_make_anon(bs); > > QTAILQ_REMOVE(&all_bdrv_states, bs, bs_list); > + qemu_event_destroy(&bs->in_flight_event); > > g_free(bs); > } > diff --git a/block/io.c b/block/io.c > index 04b52c8..ea0546f 100644 > --- a/block/io.c > +++ b/block/io.c > @@ -251,11 +251,24 @@ static void bdrv_drain_recurse(BlockDriverState *bs) > > static bool bdrv_drain_io_recurse(BlockDriverState *bs) > { > - BdrvChild *child; > + AioContext *ctx = bdrv_get_aio_context(bs); > bool waited = false; > + BdrvChild *child; > > while (atomic_read(&bs->in_flight) > 0) { > - aio_poll(bdrv_get_aio_context(bs), true); > + if (aio_context_in_iothread(ctx)) { > + /* This case should not occur at all, except for the > + * main thread. > + */ Maybe assert ctx == qemu_get_aio_context()? > + aio_poll(bdrv_get_aio_context(bs), true); > + } else { > + qemu_event_reset(&bs->in_flight_event); > + if (atomic_read(&bs->in_flight) > 0) { > + aio_context_release(bdrv_get_aio_context(bs)); > + qemu_event_wait(&bs->in_flight_event); > + aio_context_acquire(bdrv_get_aio_context(bs)); > + } > + } > waited = true; > } > > @@ -465,7 +478,9 @@ void bdrv_inc_in_flight(BlockDriverState *bs) > > void bdrv_dec_in_flight(BlockDriverState *bs) > { > - atomic_dec(&bs->in_flight); > + if (atomic_fetch_dec(&bs->in_flight) == 1) { > + qemu_event_set(&bs->in_flight_event); > + } > } > > static bool coroutine_fn wait_serialising_requests(BdrvTrackedRequest *self) > diff --git a/include/block/block_int.h b/include/block/block_int.h > index 89c38c0..9c96d5d 100644 > --- a/include/block/block_int.h > +++ b/include/block/block_int.h > @@ -404,9 +404,12 @@ struct BlockDriverState { > /* Callback before write request is processed */ > NotifierWithReturnList before_write_notifiers; > > - /* number of in-flight requests; overall and serialising */ > + /* number of in-flight requests; overall and serialising. > + * in_flight_event is set when in_flight becomes 0. > + */ > unsigned int in_flight; > unsigned int serialising_in_flight; > + QemuEvent in_flight_event; > > /* I/O throttling. > * throttle_state tells us if this BDS has I/O limits configured. > -- > 2.5.0 > > >