linux-kernel - Re: [PATCH v2] btrfs: fix allocation of bitmap pages.

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Date:   Tue, 27 Aug 2019 11:54:57 +1000
From:   Michael Ellerman <mpe@...erman.id.au>
To:     David Sterba <dsterba@...e.cz>, Nikolay Borisov <nborisov@...e.com>
Cc:     dsterba@...e.cz, Christophe Leroy <christophe.leroy@....fr>,
        erhard_f@...lbox.org, Chris Mason <clm@...com>,
        Josef Bacik <josef@...icpanda.com>,
        David Sterba <dsterba@...e.com>,
        Andrew Morton <akpm@...ux-foundation.org>, linux-mm@...ck.org,
        stable@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org,
        linux-kernel@...r.kernel.org, linux-btrfs@...r.kernel.org
Subject: Re: [PATCH v2] btrfs: fix allocation of bitmap pages.

David Sterba <dsterba@...e.cz> writes:
> On Mon, Aug 26, 2019 at 06:40:24PM +0300, Nikolay Borisov wrote:
>> >> Link: https://bugzilla.kernel.org/show_bug.cgi?id=204371
>> >> Fixes: 69d2480456d1 ("btrfs: use copy_page for copying pages instead of memcpy")
>> >> Cc: stable@...r.kernel.org
>> >> Signed-off-by: Christophe Leroy <christophe.leroy@....fr>
>> >> ---
>> >> v2: Using kmem_cache instead of get_zeroed_page() in order to benefit from SLAB debugging features like redzone.
>> > 
>> > I'll take this version, thanks. Though I'm not happy about the allocator
>> > behaviour. The kmem cache based fix can be backported independently to
>> > 4.19 regardless of the SL*B fixes.
>> > 
>> >> +extern struct kmem_cache *btrfs_bitmap_cachep;
>> > 
>> > I've renamed the cache to btrfs_free_space_bitmap_cachep
>> > 
>> > Reviewed-by: David Sterba <dsterba@...e.com>
>> 
>> Isn't this obsoleted by
>> 
>> '[PATCH v2 0/2] guarantee natural alignment for kmalloc()' ?
>
> Yeah, but this would add maybe another whole dev cycle to merge and
> release. The reporters of the bug seem to care enough to identify the
> problem and propose the fix so I feel like adding the btrfs-specific fix
> now is a little favor we can afford.
>
> The bug is reproduced on an architecture that's not widely tested so
> from practical POV I think this adds more coverage which is desirable.

Thanks.

cheers