md/raid1: ensure device failure recorded before write request returns.

When a write to one of the legs of a RAID1 fails, the failure is
recorded in the metadata of the other leg(s) so that after a restart
the data on the failed drive wont be trusted even if that drive seems
to be working again  (maybe a cable was unplugged).

Similarly when we record a bad-block in response to a write failure,
we must not let the write complete until the bad-block update is safe.

Currently there is no interlock between the write request completing
and the metadata update.  So it is possible that the write will
complete, the app will confirm success in some way, and then the
machine will crash before the metadata update completes.

This is an extremely small hole for a racy to fit in, but it is
theoretically possible and so should be closed.

So:
 - set MD_CHANGE_PENDING when requesting a metadata update for a
   failed device, so we can know with certainty when it completes
 - queue requests that experienced an error on a new queue which
   is only processed after the metadata update completes
 - call raid_end_bio_io() on bios in that queue when the time comes.

Signed-off-by: NeilBrown <neilb@suse.com>

diff --git a/drivers/md/md.c b/drivers/md/md.c
index 7d5a6cede9b07888167cd5fd250238085c2b53b1..8644ce76e5f86de8c75c16b2cb4088d23de25358 100644 (file)
--- a/drivers/md/md.c
+++ b/drivers/md/md.c
@@ -8629,6 +8629,7 @@ int rdev_set_badblocks(struct md_rdev *rdev, sector_t s, int sectors,
                /* Make sure they get written out promptly */
                sysfs_notify_dirent_safe(rdev->sysfs_state);
                set_bit(MD_CHANGE_CLEAN, &rdev->mddev->flags);
+               set_bit(MD_CHANGE_PENDING, &rdev->mddev->flags);
                md_wakeup_thread(rdev->mddev->thread);
        }
        return rv;

diff --git a/drivers/md/raid1.c b/drivers/md/raid1.c
index 742b50794dfd6d10c9230a46ea6643fe2af4038c..3d9ca836247f6034390e132f9f0cdf3f35980c47 100644 (file)
--- a/drivers/md/raid1.c
+++ b/drivers/md/raid1.c
@@ -1508,6 +1508,7 @@ static void error(struct mddev *mddev, struct md_rdev *rdev)
         */
        set_bit(MD_RECOVERY_INTR, &mddev->recovery);
        set_bit(MD_CHANGE_DEVS, &mddev->flags);
+       set_bit(MD_CHANGE_PENDING, &mddev->flags);
        printk(KERN_ALERT
               "md/raid1:%s: Disk failure on %s, disabling device.\n"
               "md/raid1:%s: Operation continuing on %d devices.\n",
@@ -2289,6 +2290,7 @@ static void handle_sync_write_finished(struct r1conf *conf, struct r1bio *r1_bio
 static void handle_write_finished(struct r1conf *conf, struct r1bio *r1_bio)
 {
        int m;
+       bool fail = false;
        for (m = 0; m < conf->raid_disks * 2 ; m++)
                if (r1_bio->bios[m] == IO_MADE_GOOD) {
                        struct md_rdev *rdev = conf->mirrors[m].rdev;
@@ -2301,6 +2303,7 @@ static void handle_write_finished(struct r1conf *conf, struct r1bio *r1_bio)
                         * narrow down and record precise write
                         * errors.
                         */
+                       fail = true;
                        if (!narrow_write_error(r1_bio, m)) {
                                md_error(conf->mddev,
                                         conf->mirrors[m].rdev);
@@ -2312,7 +2315,13 @@ static void handle_write_finished(struct r1conf *conf, struct r1bio *r1_bio)
                }
        if (test_bit(R1BIO_WriteError, &r1_bio->state))
                close_write(r1_bio);
-       raid_end_bio_io(r1_bio);
+       if (fail) {
+               spin_lock_irq(&conf->device_lock);
+               list_add(&r1_bio->retry_list, &conf->bio_end_io_list);
+               spin_unlock_irq(&conf->device_lock);
+               md_wakeup_thread(conf->mddev->thread);
+       } else
+               raid_end_bio_io(r1_bio);
 }
 
 static void handle_read_error(struct r1conf *conf, struct r1bio *r1_bio)
@@ -2418,6 +2427,23 @@ static void raid1d(struct md_thread *thread)
 
        md_check_recovery(mddev);
 
+       if (!list_empty_careful(&conf->bio_end_io_list) &&
+           !test_bit(MD_CHANGE_PENDING, &mddev->flags)) {
+               LIST_HEAD(tmp);
+               spin_lock_irqsave(&conf->device_lock, flags);
+               if (!test_bit(MD_CHANGE_PENDING, &mddev->flags)) {
+                       list_add(&tmp, &conf->bio_end_io_list);
+                       list_del_init(&conf->bio_end_io_list);
+               }
+               spin_unlock_irqrestore(&conf->device_lock, flags);
+               while (!list_empty(&tmp)) {
+                       r1_bio = list_first_entry(&conf->bio_end_io_list,
+                                                 struct r1bio, retry_list);
+                       list_del(&r1_bio->retry_list);
+                       raid_end_bio_io(r1_bio);
+               }
+       }
+
        blk_start_plug(&plug);
        for (;;) {
 
@@ -2819,6 +2845,7 @@ static struct r1conf *setup_conf(struct mddev *mddev)
        conf->raid_disks = mddev->raid_disks;
        conf->mddev = mddev;
        INIT_LIST_HEAD(&conf->retry_list);
+       INIT_LIST_HEAD(&conf->bio_end_io_list);
 
        spin_lock_init(&conf->resync_lock);
        init_waitqueue_head(&conf->wait_barrier);

diff --git a/drivers/md/raid1.h b/drivers/md/raid1.h
index 14ebb288c1ef9446fcde8596ed5191ab50431cc3..c52d7139c5d761b9385e3495fe2c0a89aca1f9e6 100644 (file)
--- a/drivers/md/raid1.h
+++ b/drivers/md/raid1.h
@@ -61,6 +61,11 @@ struct r1conf {
         * block, or anything else.
         */
        struct list_head        retry_list;
+       /* A separate list of r1bio which just need raid_end_bio_io called.
+        * This mustn't happen for writes which had any errors if the superblock
+        * needs to be written.
+        */
+       struct list_head        bio_end_io_list;
 
        /* queue pending writes to be submitted on unplug */
        struct bio_list         pending_bio_list;