From: Kevin Wolf <kwolf@redhat.com>
To: Andrey Shinkevich <andrey.shinkevich@virtuozzo.com>
Cc: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>,
"berrange@redhat.com" <berrange@redhat.com>,
Denis Lunev <den@virtuozzo.com>,
"qemu-block@nongnu.org" <qemu-block@nongnu.org>,
"qemu-devel@nongnu.org" <qemu-devel@nongnu.org>,
"mreitz@redhat.com" <mreitz@redhat.com>,
Roman Kagan <rkagan@virtuozzo.com>
Subject: Re: [Qemu-devel] [PATCH v2 7/7] iotests: new file to suppress Valgrind errors
Date: Tue, 25 Jun 2019 10:13:31 +0200 [thread overview]
Message-ID: <20190625081331.GB5187@localhost.localdomain> (raw)
In-Reply-To: <09632364-3d1d-9e5c-a050-f48f76d2e38c@virtuozzo.com>
Am 24.06.2019 um 18:55 hat Andrey Shinkevich geschrieben:
>
>
> On 17/06/2019 14:45, Kevin Wolf wrote:
> > Am 11.06.2019 um 20:02 hat Andrey Shinkevich geschrieben:
> >> The Valgrind tool reports about an uninitialised memory usage when the
> >> initialization is actually not needed. For example, the buffer 'buf'
> >> instantiated on a stack of the function guess_disk_lchs().
> >
> > I would be careful with calling initialisation "not needed". It means
> > that the test case may not behave entirely determinstic because the
> > uninitialised memory can vary between runs.\
>
> I am going to amend the comment.
>
> Andrey
>
> >
> > In this specific case, I assume that guess_disk_lchs() is called for a
> > null block node, for which .bdrv_co_preadv by default returns without
> > actually writing to the buffer. Instead of ignoring the valgrind error,
> > we could instead pass read-zeroes=on to the null block driver to make
> > the test deterministic.
>
> The buffer that the Valgrind complains of is initialized by the
> following function call blk_pread_unthrottled() that reads the first
> BDRV_SECTOR_SIZE bytes form a disk "to guess the disk logical geometry".
> The Valgrind does not recognize that way of initialization. I believe we
> do not need to zero the buffer instantiated on the stack just to make
> the Valgrind silent there.
My point is that blk_pread_unthrottled() with null-co/null-aio leaves
the buffer untouched if read-zeroes=off (which is the default). So yes,
valgrind is right, this memory is still uninitialised after
blk_pread_unthrottled().
Kevin
prev parent reply other threads:[~2019-06-25 8:15 UTC|newest]
Thread overview: 33+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-06-11 18:02 [Qemu-devel] [PATCH v2 0/7] Allow Valgrind checking all QEMU processes Andrey Shinkevich
2019-06-11 18:02 ` [Qemu-devel] [PATCH v2 1/7] iotests: allow " Andrey Shinkevich
2019-06-13 9:44 ` Vladimir Sementsov-Ogievskiy
2019-06-27 15:08 ` Andrey Shinkevich
2019-06-13 9:45 ` Vladimir Sementsov-Ogievskiy
2019-06-11 18:02 ` [Qemu-devel] [PATCH v2 2/7] iotests: exclude killed processes from running under Valgrind Andrey Shinkevich
2019-06-13 9:47 ` Vladimir Sementsov-Ogievskiy
2019-06-17 11:57 ` Roman Kagan
2019-06-17 11:15 ` Kevin Wolf
2019-06-17 12:18 ` Roman Kagan
2019-06-17 12:53 ` Kevin Wolf
2019-06-17 13:20 ` Roman Kagan
2019-06-17 14:51 ` Kevin Wolf
2019-06-24 16:55 ` Andrey Shinkevich
2019-06-11 18:02 ` [Qemu-devel] [PATCH v2 3/7] iotests: Valgrind fails to work with nonexistent directory Andrey Shinkevich
2019-06-13 9:52 ` Vladimir Sementsov-Ogievskiy
2019-06-17 11:22 ` Kevin Wolf
2019-06-11 18:02 ` [Qemu-devel] [PATCH v2 4/7] iotests: extended timeout under Valgrind Andrey Shinkevich
2019-06-13 9:54 ` Vladimir Sementsov-Ogievskiy
2019-06-11 18:02 ` [Qemu-devel] [PATCH v2 5/7] iotests: extend sleeping time " Andrey Shinkevich
2019-06-13 9:55 ` Vladimir Sementsov-Ogievskiy
2019-06-11 18:02 ` [Qemu-devel] [PATCH v2 6/7] iotests: amend QEMU NBD process synchronization Andrey Shinkevich
2019-06-13 9:59 ` Vladimir Sementsov-Ogievskiy
2019-06-17 12:45 ` Roman Kagan
2019-06-17 12:38 ` Roman Kagan
2019-06-11 18:02 ` [Qemu-devel] [PATCH v2 7/7] iotests: new file to suppress Valgrind errors Andrey Shinkevich
2019-06-13 10:06 ` Vladimir Sementsov-Ogievskiy
2019-06-24 16:55 ` Andrey Shinkevich
2019-06-24 17:09 ` Eric Blake
2019-06-24 17:23 ` Andrey Shinkevich
2019-06-17 11:45 ` Kevin Wolf
2019-06-24 16:55 ` Andrey Shinkevich
2019-06-25 8:13 ` Kevin Wolf [this message]
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