From: Paolo Bonzini <pbonzini@redhat.com>
To: Stefan Weil <sw@weilnetz.de>,
Stefan Hajnoczi <stefanha@redhat.com>,
Max Reitz <mreitz@redhat.com>
Cc: Kevin Wolf <kwolf@redhat.com>,
qemu-devel@nongnu.org, qemu-block@nongnu.org,
qemu-stable@nongnu.org
Subject: Re: [Qemu-devel] [PATCH v2] block/vdi: Add locking for parallel requests
Date: Fri, 27 Feb 2015 18:35:04 +0100 [thread overview]
Message-ID: <54F0AAC8.3010706@redhat.com> (raw)
In-Reply-To: <54F0A86E.7000608@weilnetz.de>
On 27/02/2015 18:25, Stefan Weil wrote:
> block/vdi.c was never written for multi-threaded access, see my comment
> in the header of block/vdi.c:
It is not using threads, only coroutines. Preemption points of
coroutines are well defined, and I think that the bug could be present
even in the initial AIO-based version.
> * The code is not thread safe (missing locks for changes in header and
> * block table, no problem with current QEMU).
>
> This was true in the past, but obviously later multi-threaded access was
> introduced for QEMU. Locking was added for qcow2 and other drivers in
> 2012 and 2013, but never for vdi.
qcow2 already had locking (based on AsyncContexts) before the conversion
to coroutines. Other drivers implicitly had locking because they were
synchronous; locking was added because the conversion to coroutines made
them asynchronous.
vdi never got its locking because it was already asynchronous.
Paolo
next prev parent reply other threads:[~2015-02-27 17:35 UTC|newest]
Thread overview: 20+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-02-27 14:05 [Qemu-devel] [PATCH v2] block/vdi: Add locking for parallel requests Max Reitz
2015-02-27 16:57 ` Stefan Hajnoczi
2015-02-27 16:57 ` Max Reitz
2015-02-27 17:25 ` Stefan Weil
2015-02-27 17:28 ` Max Reitz
2015-02-27 17:34 ` Stefan Weil
2015-02-27 18:07 ` Stefan Weil
2015-02-27 18:09 ` Max Reitz
2015-02-27 18:12 ` Stefan Weil
2015-02-27 18:15 ` Max Reitz
2015-02-27 18:55 ` Max Reitz
2015-02-27 20:21 ` Stefan Weil
2015-02-27 20:23 ` Max Reitz
2015-02-27 20:37 ` Stefan Weil
2015-02-27 17:35 ` Paolo Bonzini [this message]
2015-02-27 17:42 ` Paolo Bonzini
2015-02-27 18:09 ` Max Reitz
2015-02-27 18:27 ` Max Reitz
2015-02-27 21:44 ` Stefan Weil
2015-02-27 21:46 ` Max Reitz
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