From: Fam Zheng <famz@redhat.com>
To: Kevin Wolf <kwolf@redhat.com>
Cc: Jeff Cody <jcody@redhat.com>,
qemu-block@nongnu.org, qemu-devel@nongnu.org,
Stefan Hajnoczi <stefanha@redhat.com>
Subject: Re: [Qemu-devel] [PATCH 1/3] block: Don't wait serialising for non-COR read requests
Date: Tue, 1 Dec 2015 18:26:58 +0800 [thread overview]
Message-ID: <20151201102658.GA6787@ad.usersys.redhat.com> (raw)
In-Reply-To: <20151201095436.GC6527@noname.str.redhat.com>
On Tue, 12/01 10:54, Kevin Wolf wrote:
> Am 01.12.2015 um 10:36 hat Fam Zheng geschrieben:
> > The assertion problem was noticed in 06c3916b35a, but it wasn't
> > completely fixed, because even though the req is not marked as
> > serialising, it still gets serialised by wait_serialising_requests
> > against other serialising requests, which could lead to the same
> > assertion failure.
> >
> > Fix it by even more explicitly skipping the serialising for this
> > specific case.
> >
> > Signed-off-by: Fam Zheng <famz@redhat.com>
>
> And this, my friends, is another example why read/write notifiers are
> wrong and should die sooner rather than later. </broken-record>
>
Yes, I agree, except it's not clear to me what a better alternative solution
should be. A immediate question is, with whatever approach we will have,
wouldn't we still need to do this sort of "reentrant" COW before the data is
overwritten?
Fam
next prev parent reply other threads:[~2015-12-01 10:27 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-12-01 9:36 [Qemu-devel] [PATCH 0/3] block: Fix assertion failure with before write notifier again Fam Zheng
2015-12-01 9:36 ` [Qemu-devel] [PATCH 1/3] block: Don't wait serialising for non-COR read requests Fam Zheng
2015-12-01 9:54 ` Kevin Wolf
2015-12-01 10:26 ` Fam Zheng [this message]
2015-12-01 11:00 ` Kevin Wolf
2015-12-01 9:36 ` [Qemu-devel] [PATCH 2/3] iotests: Add "add_drive_raw" method Fam Zheng
2015-12-01 9:36 ` [Qemu-devel] [PATCH 3/3] iotests: Add regresion test case for write notifier assertion failure Fam Zheng
2015-12-03 6:50 ` [Qemu-devel] [PATCH 0/3] block: Fix assertion failure with before write notifier again Stefan Hajnoczi
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