From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:52473) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1aOe1k-0006S4-Jb for qemu-devel@nongnu.org; Wed, 27 Jan 2016 23:17:49 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1aOe1j-0003Dd-F6 for qemu-devel@nongnu.org; Wed, 27 Jan 2016 23:17:48 -0500 Date: Thu, 28 Jan 2016 12:17:37 +0800 From: Fam Zheng Message-ID: <20160128041736.GN7877@ad.usersys.redhat.com> References: <1453917600-2663-1-git-send-email-mreitz@redhat.com> <1453917600-2663-15-git-send-email-mreitz@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1453917600-2663-15-git-send-email-mreitz@redhat.com> Subject: Re: [Qemu-devel] [PATCH v8 14/16] block: Rewrite bdrv_close_all() List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Max Reitz Cc: Kevin Wolf , Alberto Garcia , qemu-block@nongnu.org, John Snow , qemu-devel@nongnu.org, Paolo Bonzini On Wed, 01/27 18:59, Max Reitz wrote: > This patch rewrites bdrv_close_all(): Until now, all root BDSs have been > force-closed. This is bad because it can lead to cached data not being > flushed to disk. > > Instead, try to make all reference holders relinquish their reference > voluntarily: > > 1. All BlockBackend users are handled by making all BBs simply eject > their BDS tree. Since a BDS can never be on top of a BB, this will > not cause any of the issues as seen with the force-closing of BDSs. > The references will be relinquished and any further access to the BB > will fail gracefully. > 2. All BDSs which are owned by the monitor itself (because they do not > have a BB) are relinquished next. > 3. Besides BBs and the monitor, block jobs and other BDSs are the only > things left that can hold a reference to BDSs. After every remaining > block job has been canceled, there should not be any BDSs left (and > the loop added here will always terminate (as long as NDEBUG is not > defined), because either all_bdrv_states will be empty or there will > not be any block job left to cancel, failing the assertion). > > Signed-off-by: Max Reitz > Reviewed-by: Kevin Wolf > --- > block.c | 45 +++++++++++++++++++++++++++++++++++++-------- > 1 file changed, 37 insertions(+), 8 deletions(-) > > diff --git a/block.c b/block.c > index f8dd4a3..478e0db 100644 > --- a/block.c > +++ b/block.c > @@ -2145,9 +2145,7 @@ static void bdrv_close(BlockDriverState *bs) > { > BdrvAioNotifier *ban, *ban_next; > > - if (bs->job) { > - block_job_cancel_sync(bs->job); > - } > + assert(!bs->job); > > /* Disable I/O limits and drain all pending throttled requests */ > if (bs->throttle_state) { > @@ -2213,13 +2211,44 @@ static void bdrv_close(BlockDriverState *bs) > void bdrv_close_all(void) > { > BlockDriverState *bs; > + AioContext *aio_context; > + int original_refcount = 0; > > - QTAILQ_FOREACH(bs, &bdrv_states, device_list) { > - AioContext *aio_context = bdrv_get_aio_context(bs); > + /* Drop references from requests still in flight, such as canceled block > + * jobs whose AIO context has not been polled yet */ > + bdrv_drain_all(); > > - aio_context_acquire(aio_context); > - bdrv_close(bs); > - aio_context_release(aio_context); > + blockdev_close_all_bdrv_states(); > + blk_remove_all_bs(); This (monitor before BB) doesn't match the order in the commit message (BB before monitor). > + > + /* Cancel all block jobs */ > + while (!QTAILQ_EMPTY(&all_bdrv_states)) { > + QTAILQ_FOREACH(bs, &all_bdrv_states, bs_list) { > + aio_context = bdrv_get_aio_context(bs); > + > + aio_context_acquire(aio_context); > + if (bs->job) { > + /* So we can safely query the current refcount */ > + bdrv_ref(bs); > + original_refcount = bs->refcnt; > + > + block_job_cancel_sync(bs->job); > + aio_context_release(aio_context); > + break; > + } > + aio_context_release(aio_context); > + } > + > + /* All the remaining BlockDriverStates are referenced directly or > + * indirectly from block jobs, so there needs to be at least one BDS > + * directly used by a block job */ > + assert(bs); > + > + /* Wait for the block job to release its reference */ > + while (bs->refcnt >= original_refcount) { > + aio_poll(aio_context, true); Why is this safe without acquiring aio_context? But oh wait, completions of block jobs are defered to main loop BH, so I think to release the reference, aio_poll(qemu_get_aio_context(), ...) is the right thing to do. This is also the problem in block_job_cancel_sync, which can dead loop waiting for job->completed flag, without processing main loop BH. Fam > + } > + bdrv_unref(bs); > } > } > > -- > 2.7.0 >