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md/raid10: stop using bi_phys_segments 

raid10 currently repurposes bi_phys_segments on each
incoming bio to count how many r10bio was used to encode the
request.

We need to know when the number of attached r10bio reaches
zero to:
1/ call bio_endio() when all IO on the bio is finished
2/ decrement ->nr_pending so that resync IO can proceed.

Now that the bio has its own __bi_remaining counter, that
can be used instead. We can call bio_inc_remaining to
increment the counter and call bio_endio() every time an
r10bio completes, rather than only when bi_phys_segments
reaches zero.

This addresses point 1, but not point 2.  bio_endio()
doesn't (and cannot) report when the last r10bio has
finished, so a different approach is needed.

So: instead of counting bios in ->nr_pending, count r10bios.
i.e. every time we attach a bio, increment nr_pending.
Every time an r10bio completes, decrement nr_pending.

Normally we only increment nr_pending after first checking
that ->barrier is zero, or some other non-trivial tests and
possible waiting.  When attaching multiple r10bios to a bio,
we only need the tests and the waiting once.  After the
first increment, subsequent increments can happen
unconditionally as they are really all part of the one
request.

So introduce inc_pending() which can be used when we know
that nr_pending is already elevated.

Note that this fixes a bug.  freeze_array() contains the line
	atomic_read(&conf->nr_pending) == conf->nr_queued+extra,
which implies that the units for ->nr_pending, ->nr_queued and extra
are the same.
->nr_queue and extra count r10_bios, but prior to this patch,
->nr_pending counted bios.  If a bio ever resulted in multiple
r10_bios (due to bad blocks), freeze_array() would not work correctly.
Now it does.

Signed-off-by: NeilBrown <neilb@suse.com>
Signed-off-by: Shaohua Li <shli@fb.com>
hifive-unleashed-5.1
NeilBrown 2017-03-15 14:05:13 +11:00 committed by Shaohua Li
parent 6b6c8110e1
commit fd16f2e848
1 changed files with 25 additions and 51 deletions
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76
drivers/md/raid10.c
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@ -301,27 +301,18 @@ static void reschedule_retry(struct r10bio *r10_bio)
static void raid_end_bio_io(struct r10bio *r10_bio)
{
struct bio *bio = r10_bio->master_bio;
int done;
struct r10conf *conf = r10_bio->mddev->private;
if (bio->bi_phys_segments) {
unsigned long flags;
spin_lock_irqsave(&conf->device_lock, flags);
bio->bi_phys_segments--;
done = (bio->bi_phys_segments == 0);
spin_unlock_irqrestore(&conf->device_lock, flags);
} else
done = 1;
if (!test_bit(R10BIO_Uptodate, &r10_bio->state))
bio->bi_error = -EIO;
if (done) {
bio_endio(bio);
/*
* Wake up any possible resync thread that waits for the device
* to go idle.
*/
allow_barrier(conf);
}
bio_endio(bio);
/*
* Wake up any possible resync thread that waits for the device
* to go idle.
*/
allow_barrier(conf);
free_r10bio(r10_bio);
}
@ -985,6 +976,15 @@ static void wait_barrier(struct r10conf *conf)
spin_unlock_irq(&conf->resync_lock);
}
static void inc_pending(struct r10conf *conf)
{
/* The current request requires multiple r10_bio, so
* we need to increment the pending count.
*/
WARN_ON(!atomic_read(&conf->nr_pending));
atomic_inc(&conf->nr_pending);
}
static void allow_barrier(struct r10conf *conf)
{
if ((atomic_dec_and_test(&conf->nr_pending)) ||
@ -1162,12 +1162,8 @@ read_again:
sectors_handled = (r10_bio->sector + max_sectors
- bio->bi_iter.bi_sector);
r10_bio->sectors = max_sectors;
spin_lock_irq(&conf->device_lock);
if (bio->bi_phys_segments == 0)
bio->bi_phys_segments = 2;
else
bio->bi_phys_segments++;
spin_unlock_irq(&conf->device_lock);
inc_pending(conf);
bio_inc_remaining(bio);
/*
* Cannot call generic_make_request directly as that will be
* queued in __generic_make_request and subsequent
@ -1262,9 +1258,7 @@ static void raid10_write_request(struct mddev *mddev, struct bio *bio,
* on which we have seen a write error, we want to avoid
* writing to those blocks. This potentially requires several
* writes to write around the bad blocks. Each set of writes
* gets its own r10_bio with a set of bios attached. The number
* of r10_bios is recored in bio->bi_phys_segments just as with
* the read case.
* gets its own r10_bio with a set of bios attached.
*/
r10_bio->read_slot = -1; /* make sure repl_bio gets freed */
@ -1495,15 +1489,9 @@ retry_write:
*/
if (sectors_handled < bio_sectors(bio)) {
/* We need another r10_bio and it needs to be counted
* in bio->bi_phys_segments.
*/
spin_lock_irq(&conf->device_lock);
if (bio->bi_phys_segments == 0)
bio->bi_phys_segments = 2;
else
bio->bi_phys_segments++;
spin_unlock_irq(&conf->device_lock);
/* We need another r10_bio and it needs to be counted */
inc_pending(conf);
bio_inc_remaining(bio);
one_write_done(r10_bio);
r10_bio = mempool_alloc(conf->r10bio_pool, GFP_NOIO);
@ -1532,16 +1520,6 @@ static void __make_request(struct mddev *mddev, struct bio *bio)
r10_bio->sector = bio->bi_iter.bi_sector;
r10_bio->state = 0;
/*
* We might need to issue multiple reads to different devices if there
* are bad blocks around, so we keep track of the number of reads in
* bio->bi_phys_segments. If this is 0, there is only one r10_bio and
* no locking will be needed when the request completes. If it is
* non-zero, then it is the number of not-completed requests.
*/
bio->bi_phys_segments = 0;
bio_clear_flag(bio, BIO_SEG_VALID);
if (bio_data_dir(bio) == READ)
raid10_read_request(mddev, bio, r10_bio);
else
@ -2693,12 +2671,8 @@ read_more:
r10_bio->sector + max_sectors
- mbio->bi_iter.bi_sector;
r10_bio->sectors = max_sectors;
spin_lock_irq(&conf->device_lock);
if (mbio->bi_phys_segments == 0)
mbio->bi_phys_segments = 2;
else
mbio->bi_phys_segments++;
spin_unlock_irq(&conf->device_lock);
bio_inc_remaining(mbio);
inc_pending(conf);
generic_make_request(bio);
r10_bio = mempool_alloc(conf->r10bio_pool,