On Wed, 6 Apr 2016, Ming Lei wrote:
> After arbitrary bio size is supported, the incoming bio may
> be very big. We have to split the bio into small bios so that
> each holds at most BIO_MAX_PAGES bvecs for safety reason, such
> as bio_clone().
>
> This patch fixes the following kernel crash:
>
> > [ 172.660142] BUG: unable to handle kernel NULL pointer dereference at
> > 0000000000000028
> > [ 172.660229] IP: [<ffffffff811e53b4>] bio_trim+0xf/0x2a
> > [ 172.660289] PGD 7faf3e067 PUD 7f9279067 PMD 0
> > [ 172.660399] Oops: 0000 [#1] SMP
> > [...]
> > [ 172.664780] Call Trace:
> > [ 172.664813] [<ffffffffa007f3be>] ? raid1_make_request+0x2e8/0xad7
> > [raid1]
> > [ 172.664846] [<ffffffff811f07da>] ? blk_queue_split+0x377/0x3d4
> > [ 172.664880] [<ffffffffa005fb5f>] ? md_make_request+0xf6/0x1e9 [md_mod]
> > [ 172.664912] [<ffffffff811eb860>] ? generic_make_request+0xb5/0x155
> > [ 172.664947] [<ffffffffa0445c89>] ? prio_io+0x85/0x95 [bcache]
> > [ 172.664981] [<ffffffffa0448252>] ? register_cache_set+0x355/0x8d0
> > [bcache]
> > [ 172.665016] [<ffffffffa04497d3>] ? register_bcache+0x1006/0x1174
> > [bcache]
>
> Fixes: 54efd50(block: make generic_make_request handle arbitrarily sized bios)
> Reported-by: Sebastian Roesner <sroesner-kernel...@roesner-online.de>
> Reported-by: Eric Wheeler <bca...@lists.ewheeler.net>
> Cc: sta...@vger.kernel.org (4.2+)
Ming Lei,
get_max_io_size doesn't appear until 4.5 based on a quick LXR check so we
won't see it in stable I don't think.
It would be nice to see this fixed in 4.1 (if affected there). Is there
another place this could be applied to be a bit more backward compatible?
-Eric
--
Eric Wheeler
> Cc: Shaohua Li <s...@fb.com>
> Signed-off-by: Ming Lei <ming....@canonical.com>
> ---
> I can reproduce the issue and verify the fix by the following approach:
> - create one raid1 over two virtio-blk
> - build bcache device over the above raid1 and another cache device.
> - set cache mode as writeback
> - run random write over ext4 on the bcache device
> - then the crash can be triggered
>
> block/blk-merge.c | 12 ++++++++++++
> 1 file changed, 12 insertions(+)
>
> diff --git a/block/blk-merge.c b/block/blk-merge.c
> index 2613531..9a8651f 100644
> --- a/block/blk-merge.c
> +++ b/block/blk-merge.c
> @@ -79,6 +79,18 @@ static inline unsigned get_max_io_size(struct
> request_queue *q,
> /* aligned to logical block size */
> sectors &= ~(mask >> 9);
>
> + /*
> + * With arbitrary bio size, the incoming bio may be very big.
> + * We have to split the bio into small bios so that each holds
> + * at most BIO_MAX_PAGES bvecs for safety reason, such as
> + * bio_clone().
> + *
> + * In the future, the limit might be converted into per-queue
> + * flag.
> + */
> + sectors = min_t(unsigned, sectors, BIO_MAX_PAGES <<
> + (PAGE_CACHE_SHIFT - 9));
> +
> return sectors;
> }
>
> --
> 1.9.1
>
>
