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| author | Mike Snitzer <snitzer@redhat.com> | 2015-03-30 13:39:09 -0400 |
|---|---|---|
| committer | Jens Axboe <axboe@fb.com> | 2015-03-31 09:45:50 -0600 |
| commit | e9637415a92cf25ad800b7fdeddcd30cce7b44ab (patch) | |
| tree | 81fb7a27d9d7803fe93745e1a3a1c5f984b8af97 /include | |
| parent | e42391cd048809d903291d07f86ed3934ce138e9 (diff) | |
| download | lwn-e9637415a92cf25ad800b7fdeddcd30cce7b44ab.tar.gz lwn-e9637415a92cf25ad800b7fdeddcd30cce7b44ab.zip | |
block: fix blk_stack_limits() regression due to lcm() change
Linux 3.19 commit 69c953c ("lib/lcm.c: lcm(n,0)=lcm(0,n) is 0, not n")
caused blk_stack_limits() to not properly stack queue_limits for stacked
devices (e.g. DM).
Fix this regression by establishing lcm_not_zero() and switching
blk_stack_limits() over to using it.
DM uses blk_set_stacking_limits() to establish the initial top-level
queue_limits that are then built up based on underlying devices' limits
using blk_stack_limits(). In the case of optimal_io_size (io_opt)
blk_set_stacking_limits() establishes a default value of 0. With commit
69c953c, lcm(0, n) is no longer n, which compromises proper stacking of
the underlying devices' io_opt.
Test:
$ modprobe scsi_debug dev_size_mb=10 num_tgts=1 opt_blks=1536
$ cat /sys/block/sde/queue/optimal_io_size
786432
$ dmsetup create node --table "0 100 linear /dev/sde 0"
Before this fix:
$ cat /sys/block/dm-5/queue/optimal_io_size
0
After this fix:
$ cat /sys/block/dm-5/queue/optimal_io_size
786432
Signed-off-by: Mike Snitzer <snitzer@redhat.com>
Cc: stable@vger.kernel.org # 3.19+
Acked-by: Martin K. Petersen <martin.petersen@oracle.com>
Signed-off-by: Jens Axboe <axboe@fb.com>
Diffstat (limited to 'include')
| -rw-r--r-- | include/linux/lcm.h | 1 |
1 files changed, 1 insertions, 0 deletions
diff --git a/include/linux/lcm.h b/include/linux/lcm.h index 7bf01d779b45..1ce79a7f1daa 100644 --- a/include/linux/lcm.h +++ b/include/linux/lcm.h @@ -4,5 +4,6 @@ #include <linux/compiler.h> unsigned long lcm(unsigned long a, unsigned long b) __attribute_const__; +unsigned long lcm_not_zero(unsigned long a, unsigned long b) __attribute_const__; #endif /* _LCM_H */ |