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Commit b17459c0 authored by Shaohua Li's avatar Shaohua Li Committed by NeilBrown
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raid5: add a per-stripe lock 



Add a per-stripe lock to protect stripe specific data. The purpose is to reduce
lock contention of conf->device_lock.

stripe ->toread, ->towrite are protected by per-stripe lock.  Accessing bio
list of the stripe is always serialized by this lock, so adding bio to the
lists (add_stripe_bio()) and removing bio from the lists (like
ops_run_biofill()) not race.

If bio in ->read, ->written ... list are not shared by multiple stripes, we
don't need any lock to protect ->read, ->written, because STRIPE_ACTIVE will
protect them. If the bio are shared,  there are two protections:
1. bi_phys_segments acts as a reference count
2. traverse the list uses r5_next_bio, which makes traverse never access bio
not belonging to the stripe

Let's have an example:
|  stripe1 |  stripe2    |  stripe3  |
...bio1......|bio2|bio3|....bio4.....

stripe2 has 4 bios, when it's finished, it will decrement bi_phys_segments for
all bios, but only end_bio for bio2 and bio3. bio1->bi_next still points to
bio2, but this doesn't matter. When stripe1 is finished, it will not touch bio2
because of r5_next_bio check. Next time stripe1 will end_bio for bio1 and
stripe3 will end_bio bio4.

before add_stripe_bio() addes a bio to a stripe, we already increament the bio
bi_phys_segments, so don't worry other stripes release the bio.

Signed-off-by: default avatarShaohua Li <shli@fusionio.com>
Signed-off-by: default avatarNeilBrown <neilb@suse.de>
parent 7eaf7e8e

drivers/md/raid5.c

+19 −16
Original line number Diff line number Diff line
@@ -762,14 +762,12 @@ static void ops_complete_biofill(void *stripe_head_ref) 
{

	struct stripe_head *sh = stripe_head_ref;

	struct bio *return_bi = NULL;

	struct r5conf *conf = sh->raid_conf;

	int i;



	pr_debug("%s: stripe %llu\n", __func__,

		(unsigned long long)sh->sector);



	/* clear completed biofills */

	spin_lock_irq(&conf->device_lock);

	for (i = sh->disks; i--; ) {

		struct r5dev *dev = &sh->dev[i];
@@ -795,7 +793,6 @@ static void ops_complete_biofill(void *stripe_head_ref) 
			}

		}

	}

	spin_unlock_irq(&conf->device_lock);

	clear_bit(STRIPE_BIOFILL_RUN, &sh->state);



	return_io(return_bi);
@@ -807,7 +804,6 @@ static void ops_complete_biofill(void *stripe_head_ref) 
static void ops_run_biofill(struct stripe_head *sh)

{

	struct dma_async_tx_descriptor *tx = NULL;

	struct r5conf *conf = sh->raid_conf;

	struct async_submit_ctl submit;

	int i;
@@ -818,10 +814,10 @@ static void ops_run_biofill(struct stripe_head *sh) 
		struct r5dev *dev = &sh->dev[i];

		if (test_bit(R5_Wantfill, &dev->flags)) {

			struct bio *rbi;

			spin_lock_irq(&conf->device_lock);

			spin_lock_irq(&sh->stripe_lock);

			dev->read = rbi = dev->toread;

			dev->toread = NULL;

			spin_unlock_irq(&conf->device_lock);

			spin_unlock_irq(&sh->stripe_lock);

			while (rbi && rbi->bi_sector <

				dev->sector + STRIPE_SECTORS) {

				tx = async_copy_data(0, rbi, dev->page,
@@ -1157,12 +1153,12 @@ ops_run_biodrain(struct stripe_head *sh, struct dma_async_tx_descriptor *tx) 
		if (test_and_clear_bit(R5_Wantdrain, &dev->flags)) {

			struct bio *wbi;



			spin_lock_irq(&sh->raid_conf->device_lock);

			spin_lock_irq(&sh->stripe_lock);

			chosen = dev->towrite;

			dev->towrite = NULL;

			BUG_ON(dev->written);

			wbi = dev->written = chosen;

			spin_unlock_irq(&sh->raid_conf->device_lock);

			spin_unlock_irq(&sh->stripe_lock);



			while (wbi && wbi->bi_sector <

				dev->sector + STRIPE_SECTORS) {
@@ -1467,6 +1463,8 @@ static int grow_one_stripe(struct r5conf *conf) 
	init_waitqueue_head(&sh->ops.wait_for_ops);

	#endif



	spin_lock_init(&sh->stripe_lock);



	if (grow_buffers(sh)) {

		shrink_buffers(sh);

		kmem_cache_free(conf->slab_cache, sh);
@@ -2353,8 +2351,15 @@ static int add_stripe_bio(struct stripe_head *sh, struct bio *bi, int dd_idx, in 
		(unsigned long long)bi->bi_sector,

		(unsigned long long)sh->sector);





	spin_lock_irq(&conf->device_lock);

	/*

	 * If several bio share a stripe. The bio bi_phys_segments acts as a

	 * reference count to avoid race. The reference count should already be

	 * increased before this function is called (for example, in

	 * make_request()), so other bio sharing this stripe will not free the

	 * stripe. If a stripe is owned by one stripe, the stripe lock will

	 * protect it.

	 */

	spin_lock_irq(&sh->stripe_lock);

	if (forwrite) {

		bip = &sh->dev[dd_idx].towrite;

		if (*bip == NULL)
@@ -2388,7 +2393,7 @@ static int add_stripe_bio(struct stripe_head *sh, struct bio *bi, int dd_idx, in 
		if (sector >= sh->dev[dd_idx].sector + STRIPE_SECTORS)

			set_bit(R5_OVERWRITE, &sh->dev[dd_idx].flags);

	}

	spin_unlock_irq(&conf->device_lock);

	spin_unlock_irq(&sh->stripe_lock);



	pr_debug("added bi b#%llu to stripe s#%llu, disk %d.\n",

		(unsigned long long)(*bip)->bi_sector,
@@ -2404,7 +2409,7 @@ static int add_stripe_bio(struct stripe_head *sh, struct bio *bi, int dd_idx, in 


 overlap:

	set_bit(R5_Overlap, &sh->dev[dd_idx].flags);

	spin_unlock_irq(&conf->device_lock);

	spin_unlock_irq(&sh->stripe_lock);

	return 0;

}
@@ -2454,11 +2459,11 @@ handle_failed_stripe(struct r5conf *conf, struct stripe_head *sh, 
				rdev_dec_pending(rdev, conf->mddev);

			}

		}

		spin_lock_irq(&conf->device_lock);

		spin_lock_irq(&sh->stripe_lock);

		/* fail all writes first */

		bi = sh->dev[i].towrite;

		sh->dev[i].towrite = NULL;

		spin_unlock_irq(&conf->device_lock);

		spin_unlock_irq(&sh->stripe_lock);

		if (bi) {

			s->to_write--;

			bitmap_end = 1;
@@ -3192,7 +3197,6 @@ static void analyse_stripe(struct stripe_head *sh, struct stripe_head_state *s) 


	/* Now to look around and see what can be done */

	rcu_read_lock();

	spin_lock_irq(&conf->device_lock);

	for (i=disks; i--; ) {

		struct md_rdev *rdev;

		sector_t first_bad;
@@ -3338,7 +3342,6 @@ static void analyse_stripe(struct stripe_head *sh, struct stripe_head_state *s) 
				do_recovery = 1;

		}

	}

	spin_unlock_irq(&conf->device_lock);

	if (test_bit(STRIPE_SYNCING, &sh->state)) {

		/* If there is a failed device being replaced,

		 *     we must be recovering.

drivers/md/raid5.h

+1 −0
Original line number Diff line number Diff line
@@ -210,6 +210,7 @@ struct stripe_head { 
	int			disks;		/* disks in stripe */

	enum check_states	check_state;

	enum reconstruct_states reconstruct_state;

	spinlock_t		stripe_lock;

	/**

	 * struct stripe_operations

	 * @target - STRIPE_OP_COMPUTE_BLK target