From: Paolo Bonzini <pbonzini@redhat.com>
To: Stefan Hajnoczi <stefanha@redhat.com>, qemu-devel@nongnu.org
Cc: Kevin Wolf <kwolf@redhat.com>, qemu-block@nongnu.org
Subject: Re: [Qemu-devel] [PATCH v2 0/9] blockdev: fix QMP 'transaction' with IOThreads
Date: Wed, 13 Dec 2017 22:26:31 +0100 [thread overview]
Message-ID: <a8005de2-746c-cdd3-b951-e6c23a7d6c2f@redhat.com> (raw)
In-Reply-To: <20171206144550.22295-1-stefanha@redhat.com>
On 06/12/2017 15:45, Stefan Hajnoczi wrote:
> v2:
> * Use StrOrNull for x-blockdev-set-iothread iothread argument [eblake]
>
> (This is for QEMU 2.12 because this bug is not -rc4 critical)
>
> Previously AioContext was held across QMP 'transaction' in an attempt to
> achieve bdrv_drained_begin/end() semantics. Nowadays we have
> bdrv_drained_begin/end() and the AioContext lock just protects state.
> Therefore there is no reason to hold AioContext across
> .prepare/.commit/.abort/.clean() anymore.
>
> Besides being cleanup-worthy, holding AioContext also exposes a bug:
> BDRV_POLL_WHILE() doesn't support recursive AioContext locking and will hang if
> depth > 1. This is easy to trigger by submitting a transaction with 2 actions
> that touch two drives assigned to an IOThread. The IOThread's AioContext will
> be locked twice and BDRV_POLL_WHILE() will hang.
>
> BDRV_POLL_WHILE() is best fixed by eliminating the AioContext lock entirely in
> favor of fine-grained locking. I discussed some fixes for BDRV_POLL_WHILE()
> with Paolo but we came to the conclusion that it will just add complexity when
> we really want to stop using AioContext locking.
>
> Summary:
>
> * Patch 1 fixes missing AioContext lock protection
>
> * Patches 2-6 clean up excessive AioContext locked regions in QMP
> 'transaction' to solve the hang
>
> * Patches 7-9 add a qemu-iotests test case and the necessary infrastructure
>
> Stefan Hajnoczi (9):
> blockdev: hold AioContext for bdrv_unref() in
> external_snapshot_clean()
> block: don't keep AioContext acquired after
> external_snapshot_prepare()
> block: don't keep AioContext acquired after drive_backup_prepare()
> block: don't keep AioContext acquired after blockdev_backup_prepare()
> block: don't keep AioContext acquired after
> internal_snapshot_prepare()
> block: drop unused BlockDirtyBitmapState->aio_context field
> iothread: add iothread_by_id() API
> blockdev: add x-blockdev-set-iothread testing command
> qemu-iotests: add 202 external snapshots IOThread test
>
> qapi/block-core.json | 36 +++++++
> include/sysemu/iothread.h | 1 +
> blockdev.c | 258 +++++++++++++++++++++++++++++++++------------
> iothread.c | 7 ++
> tests/qemu-iotests/202 | 95 +++++++++++++++++
> tests/qemu-iotests/202.out | 11 ++
> tests/qemu-iotests/group | 1 +
> 7 files changed, 339 insertions(+), 70 deletions(-)
> create mode 100755 tests/qemu-iotests/202
> create mode 100644 tests/qemu-iotests/202.out
>
Reviewed-by: Paolo Bonzini <pbonzini@redhat.com>
prev parent reply other threads:[~2017-12-13 21:26 UTC|newest]
Thread overview: 23+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-12-06 14:45 [Qemu-devel] [PATCH v2 0/9] blockdev: fix QMP 'transaction' with IOThreads Stefan Hajnoczi
2017-12-06 14:45 ` [Qemu-devel] [PATCH v2 1/9] blockdev: hold AioContext for bdrv_unref() in external_snapshot_clean() Stefan Hajnoczi
2017-12-07 20:32 ` Eric Blake
2017-12-06 14:45 ` [Qemu-devel] [PATCH v2 2/9] block: don't keep AioContext acquired after external_snapshot_prepare() Stefan Hajnoczi
2017-12-07 20:37 ` Eric Blake
2017-12-06 14:45 ` [Qemu-devel] [PATCH v2 3/9] block: don't keep AioContext acquired after drive_backup_prepare() Stefan Hajnoczi
2017-12-07 21:27 ` Eric Blake
2017-12-06 14:45 ` [Qemu-devel] [PATCH v2 4/9] block: don't keep AioContext acquired after blockdev_backup_prepare() Stefan Hajnoczi
2017-12-07 21:39 ` Eric Blake
2017-12-06 14:45 ` [Qemu-devel] [PATCH v2 5/9] block: don't keep AioContext acquired after internal_snapshot_prepare() Stefan Hajnoczi
2017-12-07 21:46 ` Eric Blake
2017-12-06 14:45 ` [Qemu-devel] [PATCH v2 6/9] block: drop unused BlockDirtyBitmapState->aio_context field Stefan Hajnoczi
2017-12-07 21:47 ` Eric Blake
2017-12-06 14:45 ` [Qemu-devel] [PATCH v2 7/9] iothread: add iothread_by_id() API Stefan Hajnoczi
2017-12-07 21:48 ` Eric Blake
2017-12-06 14:45 ` [Qemu-devel] [PATCH v2 8/9] blockdev: add x-blockdev-set-iothread testing command Stefan Hajnoczi
2017-12-07 21:54 ` Eric Blake
2017-12-06 14:45 ` [Qemu-devel] [PATCH v2 9/9] qemu-iotests: add 202 external snapshots IOThread test Stefan Hajnoczi
2017-12-07 21:58 ` Eric Blake
2017-12-08 10:19 ` [Qemu-devel] [Qemu-block] [PATCH v2 0/9] blockdev: fix QMP 'transaction' with IOThreads Stefan Hajnoczi
2017-12-08 13:29 ` [Qemu-devel] " Kevin Wolf
2017-12-08 15:32 ` Stefan Hajnoczi
2017-12-13 21:26 ` Paolo Bonzini [this message]
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