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SubjectRe: [block] fa53228721: WARNING:at_block/blk-merge.c:#blk_rq_map_sg
On Fri, Nov 8, 2019 at 4:23 PM kernel test robot <lkp@intel.com> wrote:
>
> FYI, we noticed the following commit (built with gcc-7):
>
> commit: fa53228721876515adabc7bc74368490bd97aa3b ("block: avoid blk_bio_segment_split for small I/O operations")
> https://git.kernel.org/cgit/linux/kernel/git/axboe/linux-block.git for-5.5/block
>
> in testcase: xfstests
> with following parameters:
>
> disk: 4HDD
> fs: xfs
> test: xfs-group16
>
> test-description: xfstests is a regression test suite for xfs and other files ystems.
> test-url: git://git.kernel.org/pub/scm/fs/xfs/xfstests-dev.git
>
>
> on test machine: qemu-system-x86_64 -enable-kvm -cpu SandyBridge -smp 2 -m 8G
>
> caused below changes (please refer to attached dmesg/kmsg for entire log/backtrace):
>
>
> +---------------------------------------------+------------+------------+
> | | d2c9be89f8 | fa53228721 |
> +---------------------------------------------+------------+------------+
> | boot_successes | 12 | 0 |
> | boot_failures | 0 | 16 |
> | WARNING:at_block/blk-merge.c:#blk_rq_map_sg | 0 | 16 |
> | RIP:blk_rq_map_sg | 0 | 16 |
> | kernel_BUG_at_drivers/scsi/scsi_lib.c | 0 | 16 |
> | invalid_opcode:#[##] | 0 | 16 |
> | RIP:scsi_init_io | 0 | 16 |
> | Kernel_panic-not_syncing:Fatal_exception | 0 | 16 |
> +---------------------------------------------+------------+------------+
>
>
> If you fix the issue, kindly add following tag
> Reported-by: kernel test robot <lkp@intel.com>
>
>
> [ 203.892883] WARNING: CPU: 0 PID: 443 at block/blk-merge.c:559 blk_rq_map_sg+0x649/0x700

If the bvec crosses page boundary, and meantime its length is
<=PAGE_SIZE, this issue may be triggered, given
some device has PAGE_SIZE segment boundary limit.

The following patch should fix this issue:

diff --git a/block/blk-merge.c b/block/blk-merge.c
index f22cb6251d06..367d3358de2a 100644
--- a/block/blk-merge.c
+++ b/block/blk-merge.c
@@ -319,7 +319,8 @@ void __blk_queue_split(struct request_queue *q,
struct bio **bio,
*/
if (!q->limits.chunk_sectors &&
(*bio)->bi_vcnt == 1 &&
- (*bio)->bi_io_vec[0].bv_len <= PAGE_SIZE) {
+ ((*bio)->bi_io_vec[0].bv_len +
+ (*bio)->bi_io_vec[0].bv_offset) <= PAGE_SIZE) {
*nr_segs = 1;
break;
}
However, in case of 64K PAGE_SIZE, I guess this way is still not safe enough.

thanks,
Ming

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