With per-stripe lock and bi_phys_segments lockless, we can safely remove some
locking places of device_lock.
stripe ->read, ->toread ... are protected by per-stripe lock. Accessing bio
list of the stripe is always serialized by this lock. If bio in ->read,
->toread ... list are shared by multiple stripes, 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: Shaohua Li <shli@xxxxxxxxxxxx>
---
drivers/md/raid5.c | 60 ++++++++++++++++++++---------------------------------
1 file changed, 23 insertions(+), 37 deletions(-)
Index: linux/drivers/md/raid5.c
===================================================================
--- linux.orig/drivers/md/raid5.c 2012-06-25 14:37:18.743841116 +0800
+++ linux/drivers/md/raid5.c 2012-06-25 14:37:21.423789830 +0800
@@ -749,15 +749,13 @@ static void ops_complete_biofill(void *s
{
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);
- spin_lock(&sh->stripe_lock);
+ spin_lock_irq(&sh->stripe_lock);
for (i = sh->disks; i--; ) {
struct r5dev *dev = &sh->dev[i];
@@ -783,8 +781,7 @@ static void ops_complete_biofill(void *s
}
}
}
- spin_unlock(&sh->stripe_lock);
- spin_unlock_irq(&conf->device_lock);
+ spin_unlock_irq(&sh->stripe_lock);
clear_bit(STRIPE_BIOFILL_RUN, &sh->state);
return_io(return_bi);
@@ -796,7 +793,6 @@ static void ops_complete_biofill(void *s
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;
@@ -807,12 +803,10 @@ static void ops_run_biofill(struct strip
struct r5dev *dev = &sh->dev[i];
if (test_bit(R5_Wantfill, &dev->flags)) {
struct bio *rbi;
- spin_lock_irq(&conf->device_lock);
- spin_lock(&sh->stripe_lock);
+ spin_lock_irq(&sh->stripe_lock);
dev->read = rbi = dev->toread;
dev->toread = NULL;
- spin_unlock(&sh->stripe_lock);
- 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,
@@ -1148,14 +1142,12 @@ ops_run_biodrain(struct stripe_head *sh,
if (test_and_clear_bit(R5_Wantdrain, &dev->flags)) {
struct bio *wbi;
- spin_lock_irq(&sh->raid_conf->device_lock);
- spin_lock(&sh->stripe_lock);
+ spin_lock_irq(&sh->stripe_lock);
chosen = dev->towrite;
dev->towrite = NULL;
BUG_ON(dev->written);
wbi = dev->written = chosen;
- spin_unlock(&sh->stripe_lock);
- spin_unlock_irq(&sh->raid_conf->device_lock);
+ spin_unlock_irq(&sh->stripe_lock);
while (wbi && wbi->bi_sector <
dev->sector + STRIPE_SECTORS) {
@@ -2341,9 +2333,15 @@ static int add_stripe_bio(struct stripe_
(unsigned long long)bi->bi_sector,
(unsigned long long)sh->sector);
-
- spin_lock_irq(&conf->device_lock);
- spin_lock(&sh->stripe_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 && sh->dev[dd_idx].written == NULL)
@@ -2377,8 +2375,7 @@ static int add_stripe_bio(struct stripe_
if (sector >= sh->dev[dd_idx].sector + STRIPE_SECTORS)
set_bit(R5_OVERWRITE, &sh->dev[dd_idx].flags);
}
- spin_unlock(&sh->stripe_lock);
- 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,
@@ -2394,8 +2391,7 @@ static int add_stripe_bio(struct stripe_
overlap:
set_bit(R5_Overlap, &sh->dev[dd_idx].flags);
- spin_unlock(&sh->stripe_lock);
- spin_unlock_irq(&conf->device_lock);
+ spin_unlock_irq(&sh->stripe_lock);
return 0;
}
@@ -2445,8 +2441,7 @@ handle_failed_stripe(struct r5conf *conf
rdev_dec_pending(rdev, conf->mddev);
}
}
- spin_lock_irq(&conf->device_lock);
- spin_lock(&sh->stripe_lock);
+ spin_lock_irq(&sh->stripe_lock);
/* fail all writes first */
bi = sh->dev[i].towrite;
sh->dev[i].towrite = NULL;
@@ -2508,8 +2503,7 @@ handle_failed_stripe(struct r5conf *conf
bi = nextbi;
}
}
- spin_unlock(&sh->stripe_lock);
- spin_unlock_irq(&conf->device_lock);
+ spin_unlock_irq(&sh->stripe_lock);
if (bitmap_end)
bitmap_endwrite(conf->mddev->bitmap, sh->sector,
STRIPE_SECTORS, 0, 0);
@@ -2715,8 +2709,7 @@ static void handle_stripe_clean_event(st
struct bio *wbi, *wbi2;
int bitmap_end = 0;
pr_debug("Return write for disc %d\n", i);
- spin_lock_irq(&conf->device_lock);
- spin_lock(&sh->stripe_lock);
+ spin_lock_irq(&sh->stripe_lock);
wbi = dev->written;
dev->written = NULL;
while (wbi && wbi->bi_sector <
@@ -2731,8 +2724,7 @@ static void handle_stripe_clean_event(st
}
if (dev->towrite == NULL)
bitmap_end = 1;
- spin_unlock(&sh->stripe_lock);
- spin_unlock_irq(&conf->device_lock);
+ spin_unlock_irq(&sh->stripe_lock);
if (bitmap_end)
bitmap_endwrite(conf->mddev->bitmap,
sh->sector,
@@ -3190,8 +3182,7 @@ static void analyse_stripe(struct stripe
/* Now to look around and see what can be done */
rcu_read_lock();
- spin_lock_irq(&conf->device_lock);
- spin_lock(&sh->stripe_lock);
+ spin_lock_irq(&sh->stripe_lock);
for (i=disks; i--; ) {
struct md_rdev *rdev;
sector_t first_bad;
@@ -3337,8 +3328,7 @@ static void analyse_stripe(struct stripe
do_recovery = 1;
}
}
- spin_unlock(&sh->stripe_lock);
- spin_unlock_irq(&conf->device_lock);
+ spin_unlock_irq(&sh->stripe_lock);
if (test_bit(STRIPE_SYNCING, &sh->state)) {
/* If there is a failed device being replaced,
* we must be recovering.
@@ -4129,9 +4119,7 @@ static void make_request(struct mddev *m
if (!plugged)
md_wakeup_thread(mddev->thread);
- spin_lock_irq(&conf->device_lock);
remaining = raid5_dec_bi_active_stripes(bi);
- spin_unlock_irq(&conf->device_lock);
if (remaining == 0) {
if ( rw == WRITE )
@@ -4511,9 +4499,7 @@ static int retry_aligned_read(struct r5
release_stripe(sh);
handled++;
}
- spin_lock_irq(&conf->device_lock);
remaining = raid5_dec_bi_active_stripes(raid_bio);
- spin_unlock_irq(&conf->device_lock);
if (remaining == 0)
bio_endio(raid_bio, 0);
if (atomic_dec_and_test(&conf->active_aligned_reads))
--
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