Raid5 overrides bio->bi_phys_segments, accessing it is with device_lock hold,
which is unnecessary, We can make it lockless actually.
Signed-off-by: Shaohua Li <shli@xxxxxxxxxxxx>
---
drivers/md/raid5.c | 37 ++++++++++++++++++++++++-------------
1 file changed, 24 insertions(+), 13 deletions(-)
Index: linux/drivers/md/raid5.c
===================================================================
--- linux.orig/drivers/md/raid5.c 2012-06-01 13:43:05.594056130 +0800
+++ linux/drivers/md/raid5.c 2012-06-01 13:50:39.852349690 +0800
@@ -101,32 +101,43 @@ static inline struct bio *r5_next_bio(st
*/
static inline int raid5_bi_phys_segments(struct bio *bio)
{
- return bio->bi_phys_segments & 0xffff;
+ atomic_t *segments = (atomic_t *)&bio->bi_phys_segments;
+ return atomic_read(segments) & 0xffff;
}
static inline int raid5_bi_hw_segments(struct bio *bio)
{
- return (bio->bi_phys_segments >> 16) & 0xffff;
+ atomic_t *segments = (atomic_t *)&bio->bi_phys_segments;
+ return (atomic_read(segments) >> 16) & 0xffff;
}
static inline int raid5_dec_bi_phys_segments(struct bio *bio)
{
- --bio->bi_phys_segments;
- return raid5_bi_phys_segments(bio);
+ atomic_t *segments = (atomic_t *)&bio->bi_phys_segments;
+ return atomic_sub_return(1, segments) & 0xffff;
}
-static inline int raid5_dec_bi_hw_segments(struct bio *bio)
+static inline void raid5_inc_bi_phys_segments(struct bio *bio)
{
- unsigned short val = raid5_bi_hw_segments(bio);
-
- --val;
- bio->bi_phys_segments = (val << 16) | raid5_bi_phys_segments(bio);
- return val;
+ atomic_t *segments = (atomic_t *)&bio->bi_phys_segments;
+ atomic_inc(segments);
}
static inline void raid5_set_bi_hw_segments(struct bio *bio, unsigned int cnt)
{
- bio->bi_phys_segments = raid5_bi_phys_segments(bio) | (cnt << 16);
+ atomic_t *segments = (atomic_t *)&bio->bi_phys_segments;
+ int old, new;
+
+ do {
+ old = atomic_read(segments);
+ new = (old & 0xffff) | (cnt << 16);
+ } while (atomic_cmpxchg(segments, old, new) != old);
+}
+
+static inline void raid5_set_bi_segments(struct bio *bio, unsigned int cnt)
+{
+ atomic_t *segments = (atomic_t *)&bio->bi_phys_segments;
+ atomic_set(segments, cnt);
}
/* Find first data disk in a raid6 stripe */
@@ -2354,7 +2365,7 @@ static int add_stripe_bio(struct stripe_
if (*bip)
bi->bi_next = *bip;
*bip = bi;
- bi->bi_phys_segments++;
+ raid5_inc_bi_phys_segments(bi);
if (forwrite) {
/* check if page is covered */
@@ -3783,7 +3794,7 @@ static struct bio *remove_bio_from_retry
* this sets the active strip count to 1 and the processed
* strip count to zero (upper 8 bits)
*/
- bi->bi_phys_segments = 1; /* biased count of active stripes */
+ raid5_set_bi_segments(bi, 1); /* biased count of active stripes */
}
return bi;
--
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