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Re: [PATCH v2 06/14] block: remove AioContext locking
From: |
Kevin Wolf |
Subject: |
Re: [PATCH v2 06/14] block: remove AioContext locking |
Date: |
Wed, 20 Dec 2023 10:19:04 +0100 |
Am 19.12.2023 um 21:04 hat Stefan Hajnoczi geschrieben:
> On Tue, 19 Dec 2023 at 10:59, Kevin Wolf <kwolf@redhat.com> wrote:
> >
> > Am 05.12.2023 um 19:20 hat Stefan Hajnoczi geschrieben:
> > > This is the big patch that removes
> > > aio_context_acquire()/aio_context_release() from the block layer and
> > > affected block layer users.
> > >
> > > There isn't a clean way to split this patch and the reviewers are likely
> > > the same group of people, so I decided to do it in one patch.
> > >
> > > Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
> > > Reviewed-by: Eric Blake <eblake@redhat.com>
> > > Reviewed-by: Kevin Wolf <kwolf@redhat.com>
> > > Reviewed-by: Paul Durrant <paul@xen.org>
> >
> > > diff --git a/migration/block.c b/migration/block.c
> > > index a15f9bddcb..2bcfcbfdf6 100644
> > > --- a/migration/block.c
> > > +++ b/migration/block.c
> > > @@ -313,22 +311,10 @@ static int mig_save_device_bulk(QEMUFile *f,
> > > BlkMigDevState *bmds)
> > > block_mig_state.submitted++;
> > > blk_mig_unlock();
> > >
> > > - /* We do not know if bs is under the main thread (and thus does
> > > - * not acquire the AioContext when doing AIO) or rather under
> > > - * dataplane. Thus acquire both the iothread mutex and the
> > > - * AioContext.
> > > - *
> > > - * This is ugly and will disappear when we make bdrv_* thread-safe,
> > > - * without the need to acquire the AioContext.
> > > - */
> > > - qemu_mutex_lock_iothread();
> > > - aio_context_acquire(blk_get_aio_context(bmds->blk));
> > > bdrv_reset_dirty_bitmap(bmds->dirty_bitmap, cur_sector *
> > > BDRV_SECTOR_SIZE,
> > > nr_sectors * BDRV_SECTOR_SIZE);
> > > blk->aiocb = blk_aio_preadv(bb, cur_sector * BDRV_SECTOR_SIZE,
> > > &blk->qiov,
> > > 0, blk_mig_read_cb, blk);
> > > - aio_context_release(blk_get_aio_context(bmds->blk));
> > > - qemu_mutex_unlock_iothread();
> > >
> > > bmds->cur_sector = cur_sector + nr_sectors;
> > > return (bmds->cur_sector >= total_sectors);
> >
> > With this hunk applied, qemu-iotests 183 fails:
> >
> > (gdb) bt
> > #0 0x000055aaa7d47c09 in bdrv_graph_co_rdlock () at
> > ../block/graph-lock.c:176
> > #1 0x000055aaa7d3de2e in graph_lockable_auto_lock (x=<optimized out>) at
> > /home/kwolf/source/qemu/include/block/graph-lock.h:215
> > #2 blk_co_do_preadv_part (blk=0x7f38a4000f30, offset=0, bytes=1048576,
> > qiov=0x7f38a40250f0, qiov_offset=qiov_offset@entry=0, flags=0) at
> > ../block/block-backend.c:1340
> > #3 0x000055aaa7d3e006 in blk_aio_read_entry (opaque=0x7f38a4025140) at
> > ../block/block-backend.c:1620
> > #4 0x000055aaa7e7aa5b in coroutine_trampoline (i0=<optimized out>,
> > i1=<optimized out>) at ../util/coroutine-ucontext.c:177
> > #5 0x00007f38d14dbe90 in __start_context () at /lib64/libc.so.6
> > #6 0x00007f38b3dfa060 in ()
> > #7 0x0000000000000000 in ()
> >
> > qemu_get_current_aio_context() returns NULL now. I don't completely
> > understand why it depends on the BQL, but adding the BQL locking back
> > fixes it.
>
> Thanks for letting me know. I have reviewed migration/block.c and
> agree that taking the BQL is correct.
>
> I have inlined the fix below and will resend this patch.
Thanks, I'll squash this into the queued patch. No need to resend, as
far as I am concerned.
Kevin
[PATCH v2 05/14] graph-lock: remove AioContext locking, Stefan Hajnoczi, 2023/12/05
[PATCH v2 08/14] scsi: remove AioContext locking, Stefan Hajnoczi, 2023/12/05
[PATCH v2 06/14] block: remove AioContext locking, Stefan Hajnoczi, 2023/12/05
[PATCH v2 10/14] aio: remove aio_context_acquire()/aio_context_release() API, Stefan Hajnoczi, 2023/12/05
[PATCH v2 12/14] scsi: remove outdated AioContext lock comment, Stefan Hajnoczi, 2023/12/05
[PATCH v2 14/14] block: remove outdated AioContext locking comments, Stefan Hajnoczi, 2023/12/05
[PATCH v2 09/14] aio-wait: draw equivalence between AIO_WAIT_WHILE() and AIO_WAIT_WHILE_UNLOCKED(), Stefan Hajnoczi, 2023/12/05
[PATCH v2 11/14] docs: remove AioContext lock from IOThread docs, Stefan Hajnoczi, 2023/12/05
[PATCH v2 13/14] job: remove outdated AioContext locking comments, Stefan Hajnoczi, 2023/12/05
Re: [PATCH v2 00/14] aio: remove AioContext lock, Kevin Wolf, 2023/12/19