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md/raid1: simplify handle_read_error().
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handle_read_error() duplicates a lot of the work that raid1_read_request()
does, so it makes sense to just use that function.
This doesn't quite work as handle_read_error() relies on the same r1bio
being re-used so that, in the case of a read-only array, setting
IO_BLOCKED in r1bio->bios[] ensures read_balance() won't re-use
that device.
So we need to allow a r1bio to be passed to raid1_read_request(), and to
have that function mostly initialise the r1bio, but leave the bios[]
array untouched.

Two parts of handle_read_error() that need to be preserved are the warning
message it prints, so they are conditionally added to raid1_read_request().

Note that this highlights a minor bug on alloc_r1bio().  It doesn't
initalise the bios[] array, so it is possible that old content is there,
which might cause read_balance() to ignore some devices with no good reason.

With this change, we no longer need inc_pending(), or the sectors_handled
arg to alloc_r1bio().

As handle_read_error() is called from raid1d() and allocates memory,
there is tiny chance of a deadlock.  All element of various pools
could be queued waiting for raid1 to handle them, and there may be no
extra memory free.
Achieving guaranteed forward progress would probably require a second
thread and another mempool.  Instead of that complexity, add
__GFP_HIGH to any allocations when read1_read_request() is called
from raid1d.

Signed-off-by: NeilBrown <neilb@suse.com>
Signed-off-by: Shaohua Li <shli@fb.com>
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NeilBrown authored and Shaohua Li committed Apr 11, 2017
1 parent 5051262 commit 689389a
Showing 1 changed file with 60 additions and 80 deletions.
140 changes: 60 additions & 80 deletions drivers/md/raid1.c
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Original file line number Diff line number Diff line change
Expand Up @@ -988,16 +988,6 @@ static void wait_read_barrier(struct r1conf *conf, sector_t sector_nr)
spin_unlock_irq(&conf->resync_lock);
}

static void inc_pending(struct r1conf *conf, sector_t bi_sector)
{
/* The current request requires multiple r1_bio, so
* we need to increment the pending count, and the corresponding
* window count.
*/
int idx = sector_to_idx(bi_sector);
atomic_inc(&conf->nr_pending[idx]);
}

static void wait_barrier(struct r1conf *conf, sector_t sector_nr)
{
int idx = sector_to_idx(sector_nr);
Expand Down Expand Up @@ -1184,43 +1174,71 @@ static void raid1_unplug(struct blk_plug_cb *cb, bool from_schedule)
kfree(plug);
}

static void init_r1bio(struct r1bio *r1_bio, struct mddev *mddev, struct bio *bio)
{
r1_bio->master_bio = bio;
r1_bio->sectors = bio_sectors(bio);
r1_bio->state = 0;
r1_bio->mddev = mddev;
r1_bio->sector = bio->bi_iter.bi_sector;
}

static inline struct r1bio *
alloc_r1bio(struct mddev *mddev, struct bio *bio, sector_t sectors_handled)
alloc_r1bio(struct mddev *mddev, struct bio *bio)
{
struct r1conf *conf = mddev->private;
struct r1bio *r1_bio;

r1_bio = mempool_alloc(conf->r1bio_pool, GFP_NOIO);

r1_bio->master_bio = bio;
r1_bio->sectors = bio_sectors(bio) - sectors_handled;
r1_bio->state = 0;
r1_bio->mddev = mddev;
r1_bio->sector = bio->bi_iter.bi_sector + sectors_handled;

/* Ensure no bio records IO_BLOCKED */
memset(r1_bio->bios, 0, conf->raid_disks * sizeof(r1_bio->bios[0]));
init_r1bio(r1_bio, mddev, bio);
return r1_bio;
}

static void raid1_read_request(struct mddev *mddev, struct bio *bio,
int max_read_sectors)
int max_read_sectors, struct r1bio *r1_bio)
{
struct r1conf *conf = mddev->private;
struct raid1_info *mirror;
struct r1bio *r1_bio;
struct bio *read_bio;
struct bitmap *bitmap = mddev->bitmap;
const int op = bio_op(bio);
const unsigned long do_sync = (bio->bi_opf & REQ_SYNC);
int max_sectors;
int rdisk;
bool print_msg = !!r1_bio;
char b[BDEVNAME_SIZE];

/*
* If r1_bio is set, we are blocking the raid1d thread
* so there is a tiny risk of deadlock. So ask for
* emergency memory if needed.
*/
gfp_t gfp = r1_bio ? (GFP_NOIO | __GFP_HIGH) : GFP_NOIO;

if (print_msg) {
/* Need to get the block device name carefully */
struct md_rdev *rdev;
rcu_read_lock();
rdev = rcu_dereference(conf->mirrors[r1_bio->read_disk].rdev);
if (rdev)
bdevname(rdev->bdev, b);
else
strcpy(b, "???");
rcu_read_unlock();
}

/*
* Still need barrier for READ in case that whole
* array is frozen.
*/
wait_read_barrier(conf, bio->bi_iter.bi_sector);

r1_bio = alloc_r1bio(mddev, bio, 0);
if (!r1_bio)
r1_bio = alloc_r1bio(mddev, bio);
else
init_r1bio(r1_bio, mddev, bio);
r1_bio->sectors = max_read_sectors;

/*
Expand All @@ -1231,11 +1249,23 @@ static void raid1_read_request(struct mddev *mddev, struct bio *bio,

if (rdisk < 0) {
/* couldn't find anywhere to read from */
if (print_msg) {
pr_crit_ratelimited("md/raid1:%s: %s: unrecoverable I/O read error for block %llu\n",
mdname(mddev),
b,
(unsigned long long)r1_bio->sector);
}
raid_end_bio_io(r1_bio);
return;
}
mirror = conf->mirrors + rdisk;

if (print_msg)
pr_info_ratelimited("md/raid1:%s: redirecting sector %llu to other mirror: %s\n",
mdname(mddev),
(unsigned long long)r1_bio->sector,
bdevname(mirror->rdev->bdev, b));

if (test_bit(WriteMostly, &mirror->rdev->flags) &&
bitmap) {
/*
Expand All @@ -1249,7 +1279,7 @@ static void raid1_read_request(struct mddev *mddev, struct bio *bio,

if (max_sectors < bio_sectors(bio)) {
struct bio *split = bio_split(bio, max_sectors,
GFP_NOIO, conf->bio_split);
gfp, conf->bio_split);
bio_chain(split, bio);
generic_make_request(bio);
bio = split;
Expand All @@ -1259,7 +1289,7 @@ static void raid1_read_request(struct mddev *mddev, struct bio *bio,

r1_bio->read_disk = rdisk;

read_bio = bio_clone_fast(bio, GFP_NOIO, mddev->bio_set);
read_bio = bio_clone_fast(bio, gfp, mddev->bio_set);

r1_bio->bios[rdisk] = read_bio;

Expand Down Expand Up @@ -1331,7 +1361,7 @@ static void raid1_write_request(struct mddev *mddev, struct bio *bio,
}
wait_barrier(conf, bio->bi_iter.bi_sector);

r1_bio = alloc_r1bio(mddev, bio, 0);
r1_bio = alloc_r1bio(mddev, bio);
r1_bio->sectors = max_write_sectors;

if (conf->pending_count >= max_queued_requests) {
Expand Down Expand Up @@ -1551,7 +1581,7 @@ static void raid1_make_request(struct mddev *mddev, struct bio *bio)
bio->bi_iter.bi_sector, bio_sectors(bio));

if (bio_data_dir(bio) == READ)
raid1_read_request(mddev, bio, sectors);
raid1_read_request(mddev, bio, sectors, NULL);
else
raid1_write_request(mddev, bio, sectors);
}
Expand Down Expand Up @@ -2443,11 +2473,8 @@ static void handle_write_finished(struct r1conf *conf, struct r1bio *r1_bio)

static void handle_read_error(struct r1conf *conf, struct r1bio *r1_bio)
{
int disk;
int max_sectors;
struct mddev *mddev = conf->mddev;
struct bio *bio;
char b[BDEVNAME_SIZE];
struct md_rdev *rdev;
dev_t bio_dev;
sector_t bio_sector;
Expand All @@ -2463,7 +2490,6 @@ static void handle_read_error(struct r1conf *conf, struct r1bio *r1_bio)
*/

bio = r1_bio->bios[r1_bio->read_disk];
bdevname(bio->bi_bdev, b);
bio_dev = bio->bi_bdev->bd_dev;
bio_sector = conf->mirrors[r1_bio->read_disk].rdev->data_offset + r1_bio->sector;
bio_put(bio);
Expand All @@ -2481,58 +2507,12 @@ static void handle_read_error(struct r1conf *conf, struct r1bio *r1_bio)
}

rdev_dec_pending(rdev, conf->mddev);
allow_barrier(conf, r1_bio->sector);
bio = r1_bio->master_bio;

read_more:
disk = read_balance(conf, r1_bio, &max_sectors);
if (disk == -1) {
pr_crit_ratelimited("md/raid1:%s: %s: unrecoverable I/O read error for block %llu\n",
mdname(mddev), b, (unsigned long long)r1_bio->sector);
raid_end_bio_io(r1_bio);
} else {
const unsigned long do_sync
= r1_bio->master_bio->bi_opf & REQ_SYNC;
r1_bio->read_disk = disk;
bio = bio_clone_fast(r1_bio->master_bio, GFP_NOIO,
mddev->bio_set);
bio_trim(bio, r1_bio->sector - bio->bi_iter.bi_sector,
max_sectors);
r1_bio->bios[r1_bio->read_disk] = bio;
rdev = conf->mirrors[disk].rdev;
pr_info_ratelimited("md/raid1:%s: redirecting sector %llu to other mirror: %s\n",
mdname(mddev),
(unsigned long long)r1_bio->sector,
bdevname(rdev->bdev, b));
bio->bi_iter.bi_sector = r1_bio->sector + rdev->data_offset;
bio->bi_bdev = rdev->bdev;
bio->bi_end_io = raid1_end_read_request;
bio_set_op_attrs(bio, REQ_OP_READ, do_sync);
if (test_bit(FailFast, &rdev->flags) &&
test_bit(R1BIO_FailFast, &r1_bio->state))
bio->bi_opf |= MD_FAILFAST;
bio->bi_private = r1_bio;
if (max_sectors < r1_bio->sectors) {
/* Drat - have to split this up more */
struct bio *mbio = r1_bio->master_bio;
int sectors_handled = (r1_bio->sector + max_sectors
- mbio->bi_iter.bi_sector);
r1_bio->sectors = max_sectors;
bio_inc_remaining(mbio);
trace_block_bio_remap(bdev_get_queue(bio->bi_bdev),
bio, bio_dev, bio_sector);
generic_make_request(bio);
bio = NULL;

r1_bio = alloc_r1bio(mddev, mbio, sectors_handled);
set_bit(R1BIO_ReadError, &r1_bio->state);
inc_pending(conf, r1_bio->sector);

goto read_more;
} else {
trace_block_bio_remap(bdev_get_queue(bio->bi_bdev),
bio, bio_dev, bio_sector);
generic_make_request(bio);
}
}
/* Reuse the old r1_bio so that the IO_BLOCKED settings are preserved */
r1_bio->state = 0;
raid1_read_request(mddev, bio, r1_bio->sectors, r1_bio);
}

static void raid1d(struct md_thread *thread)
Expand Down

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