From: Matthew Wilcox <willy@infradead.org>
To: Christopher Lameter <cl@linux.com>
Cc: Michal Hocko <mhocko@kernel.org>,
Vlastimil Babka <vbabka@suse.cz>,
Andrew Morton <akpm@linux-foundation.org>,
linux-mm@kvack.org, linux-kernel@vger.kernel.org,
Pekka Enberg <penberg@kernel.org>,
David Rientjes <rientjes@google.com>,
Ming Lei <ming.lei@redhat.com>,
Dave Chinner <david@fromorbit.com>,
"Darrick J . Wong" <darrick.wong@oracle.com>,
Christoph Hellwig <hch@lst.de>,
linux-xfs@vger.kernel.org, linux-fsdevel@vger.kernel.org,
linux-block@vger.kernel.org,
James Bottomley <James.Bottomley@hansenpartnership.com>,
linux-btrfs@vger.kernel.org
Subject: Re: [PATCH v2 2/2] mm, sl[aou]b: guarantee natural alignment for kmalloc(power-of-two)
Date: Tue, 3 Sep 2019 13:53:12 -0700 [thread overview]
Message-ID: <20190903205312.GK29434@bombadil.infradead.org> (raw)
In-Reply-To: <0100016cf8c3033d-bbcc9ba3-2d59-4654-a7c2-8ba094f8a7de-000000@email.amazonses.com>
On Tue, Sep 03, 2019 at 08:13:45PM +0000, Christopher Lameter wrote:
> On Sat, 31 Aug 2019, Matthew Wilcox wrote:
>
> > > The current behavior without special alignment for these caches has been
> > > in the wild for over a decade. And this is now coming up?
> >
> > In the wild ... and rarely enabled. When it is enabled, it may or may
> > not be noticed as data corruption, or tripping other debugging asserts.
> > Users then turn off the rare debugging option.
>
> Its enabled in all full debug session as far as I know. Fedora for
> example has been running this for ages to find breakage in device drivers
> etc etc.
Are you telling me nobody uses the ramdisk driver on fedora? Because
that's one of the affected drivers.
> > > If there is an exceptional alignment requirement then that needs to be
> > > communicated to the allocator. A special flag or create a special
> > > kmem_cache or something.
> >
> > The only way I'd agree to that is if we deliberately misalign every
> > allocation that doesn't have this special flag set. Because right now,
> > breakage happens everywhere when these debug options are enabled, and
> > the very people who need to be helped are being hurt by the debugging.
>
> That is customarily occurring for testing by adding "slub_debug" to the
> kernel commandline (or adding debug kernel options) and since my
> information is that this is done frequently (and has been for over a
> decade now) I am having a hard time believing the stories of great
> breakage here. These drivers were not tested with debugging on before?
> Never ran with a debug kernel?
Whatever is being done is clearly not enough to trigger the bug. So how
about it? Create an option to slab/slub to always return misaligned
memory.
next prev parent reply other threads:[~2019-09-03 20:53 UTC|newest]
Thread overview: 40+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-08-26 11:16 [PATCH v2 0/2] guarantee natural alignment for kmalloc() Vlastimil Babka
2019-08-26 11:16 ` [PATCH v2 1/2] mm, sl[ou]b: improve memory accounting Vlastimil Babka
2019-08-26 11:16 ` [PATCH v2 2/2] mm, sl[aou]b: guarantee natural alignment for kmalloc(power-of-two) Vlastimil Babka
2019-08-28 18:45 ` Christopher Lameter
2019-08-28 19:46 ` Matthew Wilcox
2019-08-28 22:24 ` Dave Chinner
2019-08-29 7:56 ` Vlastimil Babka
2019-08-30 0:29 ` Dave Chinner
2019-08-29 7:39 ` Michal Hocko
2019-08-30 17:41 ` Christopher Lameter
2019-09-01 0:52 ` Matthew Wilcox
2019-09-03 20:13 ` Christopher Lameter
2019-09-03 20:53 ` Matthew Wilcox [this message]
2019-09-04 5:19 ` Christoph Hellwig
2019-09-04 6:40 ` Ming Lei
2019-09-04 7:20 ` Vlastimil Babka
2019-09-04 19:31 ` Christopher Lameter
2019-09-23 16:36 ` Vlastimil Babka
2019-09-23 17:17 ` David Sterba
2019-09-23 17:51 ` Darrick J. Wong
2019-09-24 20:47 ` cl
2019-09-24 20:51 ` Matthew Wilcox
2019-09-24 20:55 ` cl
2019-09-26 13:02 ` David Sterba
2019-09-24 21:19 ` Vlastimil Babka
2019-09-24 21:53 ` Dave Chinner
2019-09-24 22:21 ` Darrick J. Wong
2019-09-24 20:52 ` cl
2019-09-24 23:54 ` Andrew Morton
2019-09-25 7:17 ` Vlastimil Babka
2019-09-26 0:16 ` Christopher Lameter
2019-09-26 0:14 ` Christopher Lameter
2019-09-26 7:41 ` Vlastimil Babka
2019-09-28 1:12 ` Christopher Lameter
2019-09-30 13:32 ` Matthew Wilcox
2019-09-23 17:54 ` Roman Gushchin
2019-09-30 8:06 ` Christoph Hellwig
2019-09-30 9:23 ` Michal Hocko
2019-09-30 9:32 ` Kirill A. Shutemov
2019-09-23 18:57 ` Matthew Wilcox
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