| From | Greg Kroah-Hartman <> | Subject | [PATCH 3.19 019/101] block: fix blk_stack_limits() regression due to lcm() change | Date | Fri, 17 Apr 2015 15:28:07 +0200 |
| |
3.19-stable review patch. If anyone has any objections, please let me know.
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From: Mike Snitzer <snitzer@redhat.com>
commit e9637415a92cf25ad800b7fdeddcd30cce7b44ab upstream.
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> Acked-by: Martin K. Petersen <martin.petersen@oracle.com> Signed-off-by: Jens Axboe <axboe@fb.com> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
--- block/blk-settings.c | 6 +++--- include/linux/lcm.h | 1 + lib/lcm.c | 11 +++++++++++ 3 files changed, 15 insertions(+), 3 deletions(-)
--- a/block/blk-settings.c +++ b/block/blk-settings.c @@ -585,7 +585,7 @@ int blk_stack_limits(struct queue_limits b->physical_block_size); t->io_min = max(t->io_min, b->io_min); - t->io_opt = lcm(t->io_opt, b->io_opt); + t->io_opt = lcm_not_zero(t->io_opt, b->io_opt); t->cluster &= b->cluster; t->discard_zeroes_data &= b->discard_zeroes_data; @@ -616,7 +616,7 @@ int blk_stack_limits(struct queue_limits b->raid_partial_stripes_expensive); /* Find lowest common alignment_offset */ - t->alignment_offset = lcm(t->alignment_offset, alignment) + t->alignment_offset = lcm_not_zero(t->alignment_offset, alignment) % max(t->physical_block_size, t->io_min); /* Verify that new alignment_offset is on a logical block boundary */ @@ -643,7 +643,7 @@ int blk_stack_limits(struct queue_limits b->max_discard_sectors); t->discard_granularity = max(t->discard_granularity, b->discard_granularity); - t->discard_alignment = lcm(t->discard_alignment, alignment) % + t->discard_alignment = lcm_not_zero(t->discard_alignment, alignment) % t->discard_granularity; } --- 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 */ --- a/lib/lcm.c +++ b/lib/lcm.c @@ -12,3 +12,14 @@ unsigned long lcm(unsigned long a, unsig return 0; } EXPORT_SYMBOL_GPL(lcm); + +unsigned long lcm_not_zero(unsigned long a, unsigned long b) +{ + unsigned long l = lcm(a, b); + + if (l) + return l; + + return (b ? : a); +} +EXPORT_SYMBOL_GPL(lcm_not_zero);
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