linux-kernel - Re: [PATCH v2 2/2] mm, sl[aou]b: guarantee natural alignment for kmalloc(power-of-two)

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Date:   Wed, 4 Sep 2019 19:31:31 +0000
From:   Christopher Lameter <cl@...ux.com>
To:     Matthew Wilcox <willy@...radead.org>
cc:     Michal Hocko <mhocko@...nel.org>, Vlastimil Babka <vbabka@...e.cz>,
        Andrew Morton <akpm@...ux-foundation.org>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org, Pekka Enberg <penberg@...nel.org>,
        David Rientjes <rientjes@...gle.com>,
        Ming Lei <ming.lei@...hat.com>,
        Dave Chinner <david@...morbit.com>,
        "Darrick J . Wong" <darrick.wong@...cle.com>,
        Christoph Hellwig <hch@....de>, linux-xfs@...r.kernel.org,
        linux-fsdevel@...r.kernel.org, linux-block@...r.kernel.org,
        James Bottomley <James.Bottomley@...senpartnership.com>,
        linux-btrfs@...r.kernel.org
Subject: Re: [PATCH v2 2/2] mm, sl[aou]b: guarantee natural alignment for
 kmalloc(power-of-two)

On Tue, 3 Sep 2019, Matthew Wilcox wrote

> > 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.

How do I know? I dont run these tests.

> > 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.

It already exists

Add "slub_debug" on the kernel command line.