Re: [PATCH] bitmap: fix memset optimization on big-endian systems

Re: [PATCH] bitmap: fix memset optimization on big-endian systems

[Omar Sandoval]

On Mon, Apr 02, 2018 at 03:58:31PM -0700, Omar Sandoval wrote:
> From: Omar Sandoval <osandov@fb.com>
> 
> Commit 2a98dc028f91 introduced an optimization to bitmap_{set,clear}()
> which uses memset() when the start and length are constants aligned to a
> byte. This is wrong on big-endian systems; our bitmaps are arrays of
> unsigned long, so bit n is not at byte n / 8 in memory. This was caught
> by the Btrfs selftests, but the bitmap selftests also fail when run on a
> big-endian machine.
> 
> We can still use memset if the start and length are aligned to an
> unsigned long, so do that on big-endian. The same problem applies to the
> memcmp in bitmap_equal(), so fix it there, too.
> 
> Fixes: 2a98dc028f91 ("include/linux/bitmap.h: turn bitmap_set and bitmap_clear into memset when possible")
> Fixes: 2c6deb01525a ("bitmap: use memcmp optimisation in more situations")
> Cc: stable@kernel.org

This should be stable@vger.kernel.org, of course

Please add 21035965f60b ("bitmap: fix memset optimization on big-endian systems") to the stable tree

[Omar Sandoval]

Just wanted to make sure this doesn't get missed because I misspelled
the stable email address in the patch. It applies to v4.13+.

Re: Please add 21035965f60b ("bitmap: fix memset optimization on big-endian systems") to the stable tree

[Linus Torvalds]

On Tue, Apr 3, 2018 at 11:14 AM, Omar Sandoval <osandov@osandov.com> wrote:
> Just wanted to make sure this doesn't get missed because I misspelled
> the stable email address in the patch. It applies to v4.13+.

The "stable@kernel.org" address for a stable cc is actually better
than stable@vger" imho, because afaik it still matches Greg's
automation (that also picks up on "Fixes:" tags), and it does *not*
cause extra email flurries when people use git-send-email scripts.

iirc, we had some vendor leak a security bug early because they
actually just cc'd everybody - including the stable list - on the
not-yet-publicly-committed change.

Greg - if your automation has changed, and you actually really want
the "vger", let me know. Because I tend to just use
"stable@kernel.org"

               Linus

Re: Please add 21035965f60b ("bitmap: fix memset optimization on big-endian systems") to the stable tree

[Greg KH]

On Tue, Apr 03, 2018 at 11:57:26AM -0700, Linus Torvalds wrote:
> 
> Greg - if your automation has changed, and you actually really want
> the "vger", let me know. Because I tend to just use
> "stable@kernel.org"

Either is fine, my scripts pick up both variants.

thanks,

greg k-h

Re: [PATCH] bitmap: fix memset optimization on big-endian systems

[Sasha Levin]

Hi,

[This is an automated email]

This commit has been processed because it contains a "Fixes:" tag,
fixing commit: 2a98dc028f91 include/linux/bitmap.h: turn bitmap_set and bitmap_clear into memset when possible.

The bot has also determined it's probably a bug fixing patch. (score: 65.4067)

The bot has tested the following trees: v4.16, v4.15.15, v4.14.32.

v4.16: Build OK!
v4.15.15: Build OK!
v4.14.32: Build OK!

--
Thanks,
Sasha