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block: remove rcu_read_lock() from part_stat_lock()

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The RCU lock is required only in disk_map_sector_rcu() to lookup the
partition.  After that request holds reference to related hd_struct.

Replace get_cpu() with preempt_disable() - returned cpu index is unused.

[hch: rebased]

Signed-off-by: Konstantin Khlebnikov <khlebnikov@yandex-team.ru>
Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
This commit is contained in:
Konstantin Khlebnikov 2020-05-27 07:24:17 +02:00 committed by Jens Axboe
parent b5af37ab3a
commit 8ab1d40a64
2 changed files with 10 additions and 5 deletions
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11
block/genhd.c
View File

@ -321,11 +321,12 @@ struct hd_struct *disk_map_sector_rcu(struct gendisk *disk, sector_t sector)
struct hd_struct *part; struct hd_struct *part;
int i; int i;
rcu_read_lock();
ptbl = rcu_dereference(disk->part_tbl); ptbl = rcu_dereference(disk->part_tbl);
part = rcu_dereference(ptbl->last_lookup); part = rcu_dereference(ptbl->last_lookup);
if (part && sector_in_part(part, sector) && hd_struct_try_get(part)) if (part && sector_in_part(part, sector) && hd_struct_try_get(part))
return part; goto out_unlock;
for (i = 1; i < ptbl->len; i++) { for (i = 1; i < ptbl->len; i++) {
part = rcu_dereference(ptbl->part[i]); part = rcu_dereference(ptbl->part[i]);
@ -339,10 +340,14 @@ struct hd_struct *disk_map_sector_rcu(struct gendisk *disk, sector_t sector)
if (!hd_struct_try_get(part)) if (!hd_struct_try_get(part))
break; break;
rcu_assign_pointer(ptbl->last_lookup, part); rcu_assign_pointer(ptbl->last_lookup, part);
return part; goto out_unlock;
} }
} }
return &disk->part0;
part = &disk->part0;
out_unlock:
rcu_read_unlock();
return part;
} }
/** /**

4
include/linux/part_stat.h
View File

@ -21,8 +21,8 @@ struct disk_stats {
* *
* part_stat_read() can be called at any time. * part_stat_read() can be called at any time.
*/ */
#define part_stat_lock() ({ rcu_read_lock(); get_cpu(); }) #define part_stat_lock() preempt_disable()
#define part_stat_unlock() do { put_cpu(); rcu_read_unlock(); } while (0) #define part_stat_unlock() preempt_enable()
#define part_stat_get_cpu(part, field, cpu) \ #define part_stat_get_cpu(part, field, cpu) \
(per_cpu_ptr((part)->dkstats, (cpu))->field) (per_cpu_ptr((part)->dkstats, (cpu))->field)