md/raid1: simplify handle_read_error().

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>

1 files changed, 60 insertions, 80 deletions

diff --git a/drivers/md/raid1.c b/drivers/md/raid1.c
index 18af00c86b42..29a9aa9254c3 100644
--- a/drivers/md/raid1.c
+++ b/drivers/md/raid1.c
@@ -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);
@@ -1184,35 +1174,60 @@ 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
@@ -1220,7 +1235,10 @@ static void raid1_read_request(struct mddev *mddev, struct bio *bio,
          */
         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;
 
         /*
@@ -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) {
                 /*
@@ -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;
@@ -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;
 
@@ -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) {
@@ -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);
 }
@@ -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;
@@ -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);
@@ -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)