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Re: [PATCH 1/2] block: Fix locking in media change monitor commands
From: |
Kevin Wolf |
Subject: |
Re: [PATCH 1/2] block: Fix locking in media change monitor commands |
Date: |
Tue, 31 Oct 2023 13:50:32 +0100 |
Am 31.10.2023 um 12:54 hat Hanna Czenczek geschrieben:
> On 13.10.23 17:33, Kevin Wolf wrote:
> > blk_insert_bs() requires that the caller holds the AioContext lock for
> > the node to be inserted. Since commit c066e808e11, neglecting to do so
> > causes a crash when the child has to be moved to a different AioContext
> > to attach it to the BlockBackend.
> >
> > This fixes qmp_blockdev_insert_anon_medium(), which is called for the
> > QMP commands 'blockdev-insert-medium' and 'blockdev-change-medium', to
> > correctly take the lock.
> >
> > Cc: qemu-stable@nongnu.org
> > Fixes: https://issues.redhat.com/browse/RHEL-3922
> > Fixes: c066e808e11a5c181b625537b6c78e0de27a4801
> > Signed-off-by: Kevin Wolf <kwolf@redhat.com>
> > ---
> > block/qapi-sysemu.c | 5 +++++
> > 1 file changed, 5 insertions(+)
>
> Do we need to take the lock for the dev_ops tray callbacks, too? I suppose
> not, and it also wouldn’t really matter in light of the lock being supposed
> to go away anyway, but still thought I should ask.
Seems nobody ever bothered to define what the callbacks expects, and I
don't know either. Not taking the lock can obviously be a problem, but
taking it can also be a problem if the callback then locks a second time
and calls a synchronous function that polls.
What I do see is that callers disagree about this, so no matter what the
correct answer is, I'm almost sure there is a bug hiding somewhere.
Kevin