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Commit e7836bd6 authored by Shaohua Li's avatar Shaohua Li Committed by NeilBrown
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raid5: lockless access raid5 overrided bi_phys_segments 



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: default avatarShaohua Li <shli@fusionio.com>
Signed-off-by: default avatarNeilBrown <neilb@suse.de>
parent 4eb788df

drivers/md/raid5.c

+32 −30
Original line number Diff line number Diff line
@@ -99,34 +99,40 @@ static inline struct bio *r5_next_bio(struct bio *bio, sector_t sector) 
 * We maintain a biased count of active stripes in the bottom 16 bits of

 * bi_phys_segments, and a count of processed stripes in the upper 16 bits

 */

static inline int raid5_bi_phys_segments(struct bio *bio)

static inline int raid5_bi_processed_stripes(struct bio *bio)

{

	return bio->bi_phys_segments & 0xffff;

	atomic_t *segments = (atomic_t *)&bio->bi_phys_segments;

	return (atomic_read(segments) >> 16) & 0xffff;

}



static inline int raid5_bi_hw_segments(struct bio *bio)

static inline int raid5_dec_bi_active_stripes(struct bio *bio)

{

	return (bio->bi_phys_segments >> 16) & 0xffff;

	atomic_t *segments = (atomic_t *)&bio->bi_phys_segments;

	return atomic_sub_return(1, segments) & 0xffff;

}



static inline int raid5_dec_bi_phys_segments(struct bio *bio)

static inline void raid5_inc_bi_active_stripes(struct bio *bio)

{

	--bio->bi_phys_segments;

	return raid5_bi_phys_segments(bio);

	atomic_t *segments = (atomic_t *)&bio->bi_phys_segments;

	atomic_inc(segments);

}



static inline int raid5_dec_bi_hw_segments(struct bio *bio)

static inline void raid5_set_bi_processed_stripes(struct bio *bio,

	unsigned int cnt)

{

	unsigned short val = raid5_bi_hw_segments(bio);

	atomic_t *segments = (atomic_t *)&bio->bi_phys_segments;

	int old, new;



	--val;

	bio->bi_phys_segments = (val << 16) | raid5_bi_phys_segments(bio);

	return val;

	do {

		old = atomic_read(segments);

		new = (old & 0xffff) | (cnt << 16);

	} while (atomic_cmpxchg(segments, old, new) != old);

}



static inline void raid5_set_bi_hw_segments(struct bio *bio, unsigned int cnt)

static inline void raid5_set_bi_stripes(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;

	atomic_set(segments, cnt);

}



/* Find first data disk in a raid6 stripe */
@@ -781,7 +787,7 @@ static void ops_complete_biofill(void *stripe_head_ref) 
			while (rbi && rbi->bi_sector <

				dev->sector + STRIPE_SECTORS) {

				rbi2 = r5_next_bio(rbi, dev->sector);

				if (!raid5_dec_bi_phys_segments(rbi)) {

				if (!raid5_dec_bi_active_stripes(rbi)) {

					rbi->bi_next = return_bi;

					return_bi = rbi;

				}
@@ -2367,7 +2373,7 @@ static int add_stripe_bio(struct stripe_head *sh, struct bio *bi, int dd_idx, in 
	if (*bip)

		bi->bi_next = *bip;

	*bip = bi;

	bi->bi_phys_segments++;

	raid5_inc_bi_active_stripes(bi);



	if (forwrite) {

		/* check if page is covered */
@@ -2464,7 +2470,7 @@ handle_failed_stripe(struct r5conf *conf, struct stripe_head *sh, 
			sh->dev[i].sector + STRIPE_SECTORS) {

			struct bio *nextbi = r5_next_bio(bi, sh->dev[i].sector);

			clear_bit(BIO_UPTODATE, &bi->bi_flags);

			if (!raid5_dec_bi_phys_segments(bi)) {

			if (!raid5_dec_bi_active_stripes(bi)) {

				md_write_end(conf->mddev);

				bi->bi_next = *return_bi;

				*return_bi = bi;
@@ -2479,7 +2485,7 @@ handle_failed_stripe(struct r5conf *conf, struct stripe_head *sh, 
		       sh->dev[i].sector + STRIPE_SECTORS) {

			struct bio *bi2 = r5_next_bio(bi, sh->dev[i].sector);

			clear_bit(BIO_UPTODATE, &bi->bi_flags);

			if (!raid5_dec_bi_phys_segments(bi)) {

			if (!raid5_dec_bi_active_stripes(bi)) {

				md_write_end(conf->mddev);

				bi->bi_next = *return_bi;

				*return_bi = bi;
@@ -2503,7 +2509,7 @@ handle_failed_stripe(struct r5conf *conf, struct stripe_head *sh, 
				struct bio *nextbi =

					r5_next_bio(bi, sh->dev[i].sector);

				clear_bit(BIO_UPTODATE, &bi->bi_flags);

				if (!raid5_dec_bi_phys_segments(bi)) {

				if (!raid5_dec_bi_active_stripes(bi)) {

					bi->bi_next = *return_bi;

					*return_bi = bi;

				}
@@ -2722,7 +2728,7 @@ static void handle_stripe_clean_event(struct r5conf *conf, 
				while (wbi && wbi->bi_sector <

					dev->sector + STRIPE_SECTORS) {

					wbi2 = r5_next_bio(wbi, dev->sector);

					if (!raid5_dec_bi_phys_segments(wbi)) {

					if (!raid5_dec_bi_active_stripes(wbi)) {

						md_write_end(conf->mddev);

						wbi->bi_next = *return_bi;

						*return_bi = wbi;
@@ -3798,7 +3804,7 @@ static struct bio *remove_bio_from_retry(struct r5conf *conf) 
		 * 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_stripes(bi, 1); /* biased count of active stripes */

	}



	return bi;
@@ -4133,9 +4139,7 @@ static void make_request(struct mddev *mddev, struct bio * bi) 
		}

	}



	spin_lock_irq(&conf->device_lock);

	remaining = raid5_dec_bi_phys_segments(bi);

	spin_unlock_irq(&conf->device_lock);

	remaining = raid5_dec_bi_active_stripes(bi);

	if (remaining == 0) {



		if ( rw == WRITE )
@@ -4491,7 +4495,7 @@ static int retry_aligned_read(struct r5conf *conf, struct bio *raid_bio) 
		     sector += STRIPE_SECTORS,

		     scnt++) {



		if (scnt < raid5_bi_hw_segments(raid_bio))

		if (scnt < raid5_bi_processed_stripes(raid_bio))

			/* already done this stripe */

			continue;
@@ -4499,14 +4503,14 @@ static int retry_aligned_read(struct r5conf *conf, struct bio *raid_bio) 


		if (!sh) {

			/* failed to get a stripe - must wait */

			raid5_set_bi_hw_segments(raid_bio, scnt);

			raid5_set_bi_processed_stripes(raid_bio, scnt);

			conf->retry_read_aligned = raid_bio;

			return handled;

		}



		if (!add_stripe_bio(sh, raid_bio, dd_idx, 0)) {

			release_stripe(sh);

			raid5_set_bi_hw_segments(raid_bio, scnt);

			raid5_set_bi_processed_stripes(raid_bio, scnt);

			conf->retry_read_aligned = raid_bio;

			return handled;

		}
@@ -4515,9 +4519,7 @@ static int retry_aligned_read(struct r5conf *conf, struct bio *raid_bio) 
		release_stripe(sh);

		handled++;

	}

	spin_lock_irq(&conf->device_lock);

	remaining = raid5_dec_bi_phys_segments(raid_bio);

	spin_unlock_irq(&conf->device_lock);

	remaining = raid5_dec_bi_active_stripes(raid_bio);

	if (remaining == 0)

		bio_endio(raid_bio, 0);

	if (atomic_dec_and_test(&conf->active_aligned_reads))