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e9637415a9
Linux 3.19 commit69c953c("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 commit69c953c, 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>
25 lines
441 B
C
25 lines
441 B
C
#include <linux/compiler.h>
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#include <linux/gcd.h>
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#include <linux/export.h>
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#include <linux/lcm.h>
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/* Lowest common multiple */
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unsigned long lcm(unsigned long a, unsigned long b)
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{
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if (a && b)
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return (a / gcd(a, b)) * b;
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else
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return 0;
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}
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EXPORT_SYMBOL_GPL(lcm);
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unsigned long lcm_not_zero(unsigned long a, unsigned long b)
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{
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unsigned long l = lcm(a, b);
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if (l)
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return l;
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return (b ? : a);
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}
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EXPORT_SYMBOL_GPL(lcm_not_zero);
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