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@xxxxxxxxxx>
Cc: stable@xxxxxxxxxxxxxxx # 3.19+
---
block/blk-settings.c | 6 +++---
include/linux/lcm.h | 1 +
lib/lcm.c | 11 +++++++++++
3 files changed, 15 insertions(+), 3 deletions(-)
diff --git a/block/blk-settings.c b/block/blk-settings.c
index 6ed2cbe..12600bf 100644
--- a/block/blk-settings.c
+++ b/block/blk-settings.c
@@ -585,7 +585,7 @@ int blk_stack_limits(struct queue_limits *t, struct queue_limits *b,
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 *t, struct queue_limits *b,
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 *t, struct queue_limits *b,
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;
}
diff --git a/include/linux/lcm.h b/include/linux/lcm.h
index 7bf01d7..1ce79a7 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 */
diff --git a/lib/lcm.c b/lib/lcm.c
index e97dbd5..03d7fcb 100644
--- a/lib/lcm.c
+++ b/lib/lcm.c
@@ -12,3 +12,14 @@ unsigned long lcm(unsigned long a, unsigned long b)
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);
--
1.7.4.4
--
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