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[PATCH] md: allow reads that have bypassed the cache to be retried on failure 

If a bypass-the-cache read fails, we simply try again through the cache.  If
it fails again it will trigger normal recovery precedures.

update 1:

From: NeilBrown <neilb@suse.de>

1/
  chunk_aligned_read and retry_aligned_read assume that
      data_disks == raid_disks - 1
  which is not true for raid6.
  So when an aligned read request bypasses the cache, we can get the wrong data.

2/ The cloned bio is being used-after-free in raid5_align_endio
   (to test BIO_UPTODATE).

3/ We forgot to add rdev->data_offset when submitting
   a bio for aligned-read

4/ clone_bio calls blk_recount_segments and then we change bi_bdev,
   so we need to invalidate the segment counts.

5/ We don't de-reference the rdev when the read completes.
   This means we need to record the rdev to so it is still
   available in the end_io routine.  Fortunately
   bi_next in the original bio is unused at this point so
   we can stuff it in there.

6/ We leak a cloned bio if the target rdev is not usable.

From: NeilBrown <neilb@suse.de>

update 2:

1/ When aligned requests fail (read error) they need to be retried
   via the normal method (stripe cache).  As we cannot be sure that
   we can process a single read in one go (we may not be able to
   allocate all the stripes needed) we store a bio-being-retried
   and a list of bioes-that-still-need-to-be-retried.
   When find a bio that needs to be retried, we should add it to
   the list, not to single-bio...

2/ We were never incrementing 'scnt' when resubmitting failed
   aligned requests.

[akpm@osdl.org: build fix]
Signed-off-by: Neil Brown <neilb@suse.de>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
This commit is contained in:
Raz Ben-Jehuda(caro) 2006-12-10 02:20:47 -08:00 committed by Linus Torvalds
parent f679623f50
commit 46031f9a38
2 changed files with 163 additions and 5 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

165
drivers/md/raid5.c
View File

@ -134,6 +134,8 @@ static void __release_stripe(raid5_conf_t *conf, struct stripe_head *sh)
if (!test_bit(STRIPE_EXPANDING, &sh->state)) {
list_add_tail(&sh->lru, &conf->inactive_list);
wake_up(&conf->wait_for_stripe);
if (conf->retry_read_aligned)
md_wakeup_thread(conf->mddev->thread);
}
}
}
@ -2644,19 +2646,81 @@ static int in_chunk_boundary(mddev_t *mddev, struct bio *bio)
((sector & (chunk_sectors - 1)) + bio_sectors);
}
/*
* add bio to the retry LIFO ( in O(1) ... we are in interrupt )
* later sampled by raid5d.
*/
static void add_bio_to_retry(struct bio *bi,raid5_conf_t *conf)
{
unsigned long flags;
spin_lock_irqsave(&conf->device_lock, flags);
bi->bi_next = conf->retry_read_aligned_list;
conf->retry_read_aligned_list = bi;
spin_unlock_irqrestore(&conf->device_lock, flags);
md_wakeup_thread(conf->mddev->thread);
}
static struct bio *remove_bio_from_retry(raid5_conf_t *conf)
{
struct bio *bi;
bi = conf->retry_read_aligned;
if (bi) {
conf->retry_read_aligned = NULL;
return bi;
}
bi = conf->retry_read_aligned_list;
if(bi) {
conf->retry_read_aligned = bi->bi_next;
bi->bi_next = NULL;
bi->bi_phys_segments = 1; /* biased count of active stripes */
bi->bi_hw_segments = 0; /* count of processed stripes */
}
return bi;
}
/*
* The "raid5_align_endio" should check if the read succeeded and if it
* did, call bio_endio on the original bio (having bio_put the new bio
* first).
* If the read failed..
*/
int raid5_align_endio(struct bio *bi, unsigned int bytes , int error)
static int raid5_align_endio(struct bio *bi, unsigned int bytes, int error)
{
struct bio* raid_bi = bi->bi_private;
mddev_t *mddev;
raid5_conf_t *conf;
int uptodate = test_bit(BIO_UPTODATE, &bi->bi_flags);
mdk_rdev_t *rdev;
if (bi->bi_size)
return 1;
bio_put(bi);
bio_endio(raid_bi, bytes, error);
mddev = raid_bi->bi_bdev->bd_disk->queue->queuedata;
conf = mddev_to_conf(mddev);
rdev = (void*)raid_bi->bi_next;
raid_bi->bi_next = NULL;
rdev_dec_pending(rdev, conf->mddev);
if (!error && uptodate) {
bio_endio(raid_bi, bytes, 0);
if (atomic_dec_and_test(&conf->active_aligned_reads))
wake_up(&conf->wait_for_stripe);
return 0;
}
PRINTK("raid5_align_endio : io error...handing IO for a retry\n");
add_bio_to_retry(raid_bi, conf);
return 0;
}
@ -2665,7 +2729,7 @@ static int chunk_aligned_read(request_queue_t *q, struct bio * raid_bio)
mddev_t *mddev = q->queuedata;
raid5_conf_t *conf = mddev_to_conf(mddev);
const unsigned int raid_disks = conf->raid_disks;
const unsigned int data_disks = raid_disks - 1;
const unsigned int data_disks = raid_disks - conf->max_degraded;
unsigned int dd_idx, pd_idx;
struct bio* align_bi;
mdk_rdev_t *rdev;
@ -2699,13 +2763,25 @@ static int chunk_aligned_read(request_queue_t *q, struct bio * raid_bio)
rcu_read_lock();
rdev = rcu_dereference(conf->disks[dd_idx].rdev);
if (rdev && test_bit(In_sync, &rdev->flags)) {
align_bi->bi_bdev = rdev->bdev;
atomic_inc(&rdev->nr_pending);
rcu_read_unlock();
raid_bio->bi_next = (void*)rdev;
align_bi->bi_bdev = rdev->bdev;
align_bi->bi_flags &= ~(1 << BIO_SEG_VALID);
align_bi->bi_sector += rdev->data_offset;
spin_lock_irq(&conf->device_lock);
wait_event_lock_irq(conf->wait_for_stripe,
conf->quiesce == 0,
conf->device_lock, /* nothing */);
atomic_inc(&conf->active_aligned_reads);
spin_unlock_irq(&conf->device_lock);
generic_make_request(align_bi);
return 1;
} else {
rcu_read_unlock();
bio_put(align_bi);
return 0;
}
}
@ -3050,6 +3126,72 @@ static inline sector_t sync_request(mddev_t *mddev, sector_t sector_nr, int *ski
return STRIPE_SECTORS;
}
static int retry_aligned_read(raid5_conf_t *conf, struct bio *raid_bio)
{
/* We may not be able to submit a whole bio at once as there
* may not be enough stripe_heads available.
* We cannot pre-allocate enough stripe_heads as we may need
* more than exist in the cache (if we allow ever large chunks).
* So we do one stripe head at a time and record in
* ->bi_hw_segments how many have been done.
*
* We *know* that this entire raid_bio is in one chunk, so
* it will be only one 'dd_idx' and only need one call to raid5_compute_sector.
*/
struct stripe_head *sh;
int dd_idx, pd_idx;
sector_t sector, logical_sector, last_sector;
int scnt = 0;
int remaining;
int handled = 0;
logical_sector = raid_bio->bi_sector & ~((sector_t)STRIPE_SECTORS-1);
sector = raid5_compute_sector( logical_sector,
conf->raid_disks,
conf->raid_disks - conf->max_degraded,
&dd_idx,
&pd_idx,
conf);
last_sector = raid_bio->bi_sector + (raid_bio->bi_size>>9);
for (; logical_sector < last_sector;
logical_sector += STRIPE_SECTORS, scnt++) {
if (scnt < raid_bio->bi_hw_segments)
/* already done this stripe */
continue;
sh = get_active_stripe(conf, sector, conf->raid_disks, pd_idx, 1);
if (!sh) {
/* failed to get a stripe - must wait */
raid_bio->bi_hw_segments = scnt;
conf->retry_read_aligned = raid_bio;
return handled;
}
set_bit(R5_ReadError, &sh->dev[dd_idx].flags);
add_stripe_bio(sh, raid_bio, dd_idx, 0);
handle_stripe(sh, NULL);
release_stripe(sh);
handled++;
}
spin_lock_irq(&conf->device_lock);
remaining = --raid_bio->bi_phys_segments;
spin_unlock_irq(&conf->device_lock);
if (remaining == 0) {
int bytes = raid_bio->bi_size;
raid_bio->bi_size = 0;
raid_bio->bi_end_io(raid_bio, bytes, 0);
}
if (atomic_dec_and_test(&conf->active_aligned_reads))
wake_up(&conf->wait_for_stripe);
return handled;
}
/*
* This is our raid5 kernel thread.
*
@ -3071,6 +3213,7 @@ static void raid5d (mddev_t *mddev)
spin_lock_irq(&conf->device_lock);
while (1) {
struct list_head *first;
struct bio *bio;
if (conf->seq_flush != conf->seq_write) {
int seq = conf->seq_flush;
@ -3087,6 +3230,16 @@ static void raid5d (mddev_t *mddev)
!list_empty(&conf->delayed_list))
raid5_activate_delayed(conf);
while ((bio = remove_bio_from_retry(conf))) {
int ok;
spin_unlock_irq(&conf->device_lock);
ok = retry_aligned_read(conf, bio);
spin_lock_irq(&conf->device_lock);
if (!ok)
break;
handled++;
}
if (list_empty(&conf->handle_list))
break;
@ -3274,6 +3427,7 @@ static int run(mddev_t *mddev)
INIT_LIST_HEAD(&conf->inactive_list);
atomic_set(&conf->active_stripes, 0);
atomic_set(&conf->preread_active_stripes, 0);
atomic_set(&conf->active_aligned_reads, 0);
PRINTK("raid5: run(%s) called.\n", mdname(mddev));
@ -3796,7 +3950,8 @@ static void raid5_quiesce(mddev_t *mddev, int state)
spin_lock_irq(&conf->device_lock);
conf->quiesce = 1;
wait_event_lock_irq(conf->wait_for_stripe,
atomic_read(&conf->active_stripes) == 0,
atomic_read(&conf->active_stripes) == 0 &&
atomic_read(&conf->active_aligned_reads) == 0,
conf->device_lock, /* nothing */);
spin_unlock_irq(&conf->device_lock);
break;

3
include/linux/raid/raid5.h
View File

@ -227,7 +227,10 @@ struct raid5_private_data {
struct list_head handle_list; /* stripes needing handling */
struct list_head delayed_list; /* stripes that have plugged requests */
struct list_head bitmap_list; /* stripes delaying awaiting bitmap update */
struct bio *retry_read_aligned; /* currently retrying aligned bios */
struct bio *retry_read_aligned_list; /* aligned bios retry list */
atomic_t preread_active_stripes; /* stripes with scheduled io */
atomic_t active_aligned_reads;
atomic_t reshape_stripes; /* stripes with pending writes for reshape */
/* unfortunately we need two cache names as we temporarily have