[PATCH 14/16] block: remove rcu_read_lock() from part_stat_lock()

From: Konstantin Khlebnikov <khlebnikov(a)yandex-team.ru&gt; 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. Signed-off-by: Konstantin Khlebnikov <khlebnikov(a)yandex-team.ru&gt; [hch: rebased] Signed-off-by: Christoph Hellwig <hch(a)lst.de&gt; --- block/genhd.c | 11 ++++++++--- include/linux/part_stat.h | 4 ++-- 2 files changed, 10 insertions(+), 5 deletions(-) diff --git a/block/genhd.c b/block/genhd.c index 3e7df0a3e6bb0..1a76593276644 100644 --- a/block/genhd.c +++ b/block/genhd.c @@ -321,11 +321,12 @@ struct hd_struct *disk_map_sector_rcu(struct gendisk *disk, sector_t sector) struct hd_struct *part; int i; + rcu_read_lock(); ptbl = rcu_dereference(disk->part_tbl); part = rcu_dereference(ptbl->last_lookup); if (part && sector_in_part(part, sector) && hd_struct_try_get(part)) - return part; + goto out_unlock; for (i = 1; i < ptbl->len; 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)) break; 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; } /** diff --git a/include/linux/part_stat.h b/include/linux/part_stat.h index 6644197980b92..a6b0938ce82e9 100644 --- a/include/linux/part_stat.h +++ b/include/linux/part_stat.h @@ -21,8 +21,8 @@ struct disk_stats { * * part_stat_read() can be called at any time. */ -#define part_stat_lock() ({ rcu_read_lock(); get_cpu(); }) -#define part_stat_unlock() do { put_cpu(); rcu_read_unlock(); } while (0) +#define part_stat_lock() preempt_disable() +#define part_stat_unlock() preempt_enable() #define part_stat_get_cpu(part, field, cpu) \ (per_cpu_ptr((part)->dkstats, (cpu))->field) -- 2.26.2