On Wed, Apr 6, 2016 at 1:44 AM, Ming Lei <ming.lei@xxxxxxxxxxxxx> 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-kernelorg@xxxxxxxxxxxxxxxxx>
> Reported-by: Eric Wheeler <bcache@xxxxxxxxxxxxxxxxxx>
> Cc: stable@xxxxxxxxxxxxxxx (4.2+)
> Cc: Shaohua Li <shli@xxxxxx>
> Signed-off-by: Ming Lei <ming.lei@xxxxxxxxxxxxx>
> ---
> 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
For anyone who is interested in issue/fix, forget to mention:
The bucket size should be set as bigger than 1M during making bcache.
In my test, the bucket size is 2M.
Thanks,
Ming
>
> 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
>
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