[PATCH] md: support BIO_RW_BARRIER for md/raid1

We can only accept BARRIER requests if all slaves handle
barriers, and that can, of course, change with time....

So we keep track of whether the whole array seems safe for barriers,
and also whether each individual rdev handles barriers.

We initially assumes barriers are OK.

When writing the superblock we try a barrier, and if that fails, we flag
things for no-barriers.  This will usually clear the flags fairly quickly.

If writing the superblock finds that BIO_RW_BARRIER is -ENOTSUPP, we need to
resubmit, so introduce function "md_super_wait" which waits for requests to
finish, and retries ENOTSUPP requests without the barrier flag.

When writing the real raid1, write requests which were BIO_RW_BARRIER but
which aresn't supported need to be retried.  So raid1d is enhanced to do this,
and when any bio write completes (i.e.  no retry needed) we remove it from the
r1bio, so that devices needing retry are easy to find.

We should hardly ever get -ENOTSUPP errors when writing data to the raid.
It should only happen if:
  1/ the device used to support BARRIER, but now doesn't.  Few devices
     change like this, though raid1 can!
or
  2/ the array has no persistent superblock, so there was no opportunity to
     pre-test for barriers when writing the superblock.

Signed-off-by: Neil Brown <neilb@cse.unsw.edu.au>
Signed-off-by: Neil Brown <neilb@suse.de>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

1 files changed, 83 insertions, 16 deletions

diff --git a/drivers/md/md.c b/drivers/md/md.c
index caa4add00c1b..199016932de5 100644
--- a/drivers/md/md.c
+++ b/drivers/md/md.c
@@ -330,18 +330,46 @@ static void free_disk_sb(mdk_rdev_t * rdev)
 static int super_written(struct bio *bio, unsigned int bytes_done, int error)
 {
         mdk_rdev_t *rdev = bio->bi_private;
+        mddev_t *mddev = rdev->mddev;
         if (bio->bi_size)
                 return 1;
 
         if (error || !test_bit(BIO_UPTODATE, &bio->bi_flags))
-                md_error(rdev->mddev, rdev);
+                md_error(mddev, rdev);
 
-        if (atomic_dec_and_test(&rdev->mddev->pending_writes))
-                wake_up(&rdev->mddev->sb_wait);
+        if (atomic_dec_and_test(&mddev->pending_writes))
+                wake_up(&mddev->sb_wait);
         bio_put(bio);
         return 0;
 }
 
+static int super_written_barrier(struct bio *bio, unsigned int bytes_done, int error)
+{
+        struct bio *bio2 = bio->bi_private;
+        mdk_rdev_t *rdev = bio2->bi_private;
+        mddev_t *mddev = rdev->mddev;
+        if (bio->bi_size)
+                return 1;
+
+        if (!test_bit(BIO_UPTODATE, &bio->bi_flags) &&
+            error == -EOPNOTSUPP) {
+                unsigned long flags;
+                /* barriers don't appear to be supported :-( */
+                set_bit(BarriersNotsupp, &rdev->flags);
+                mddev->barriers_work = 0;
+                spin_lock_irqsave(&mddev->write_lock, flags);
+                bio2->bi_next = mddev->biolist;
+                mddev->biolist = bio2;
+                spin_unlock_irqrestore(&mddev->write_lock, flags);
+                wake_up(&mddev->sb_wait);
+                bio_put(bio);
+                return 0;
+        }
+        bio_put(bio2);
+        bio->bi_private = rdev;
+        return super_written(bio, bytes_done, error);
+}
+
 void md_super_write(mddev_t *mddev, mdk_rdev_t *rdev,
                    sector_t sector, int size, struct page *page)
 {
@@ -350,16 +378,54 @@ void md_super_write(mddev_t *mddev, mdk_rdev_t *rdev,
          * and decrement it on completion, waking up sb_wait
          * if zero is reached.
          * If an error occurred, call md_error
+         *
+         * As we might need to resubmit the request if BIO_RW_BARRIER
+         * causes ENOTSUPP, we allocate a spare bio...
          */
         struct bio *bio = bio_alloc(GFP_NOIO, 1);
+        int rw = (1<<BIO_RW) | (1<<BIO_RW_SYNC);
 
         bio->bi_bdev = rdev->bdev;
         bio->bi_sector = sector;
         bio_add_page(bio, page, size, 0);
         bio->bi_private = rdev;
         bio->bi_end_io = super_written;
+        bio->bi_rw = rw;
+
         atomic_inc(&mddev->pending_writes);
-        submit_bio((1<<BIO_RW)|(1<<BIO_RW_SYNC), bio);
+        if (!test_bit(BarriersNotsupp, &rdev->flags)) {
+                struct bio *rbio;
+                rw |= (1<<BIO_RW_BARRIER);
+                rbio = bio_clone(bio, GFP_NOIO);
+                rbio->bi_private = bio;
+                rbio->bi_end_io = super_written_barrier;
+                submit_bio(rw, rbio);
+        } else
+                submit_bio(rw, bio);
+}
+
+void md_super_wait(mddev_t *mddev)
+{
+        /* wait for all superblock writes that were scheduled to complete.
+         * if any had to be retried (due to BARRIER problems), retry them
+         */
+        DEFINE_WAIT(wq);
+        for(;;) {
+                prepare_to_wait(&mddev->sb_wait, &wq, TASK_UNINTERRUPTIBLE);
+                if (atomic_read(&mddev->pending_writes)==0)
+                        break;
+                while (mddev->biolist) {
+                        struct bio *bio;
+                        spin_lock_irq(&mddev->write_lock);
+                        bio = mddev->biolist;
+                        mddev->biolist = bio->bi_next ;
+                        bio->bi_next = NULL;
+                        spin_unlock_irq(&mddev->write_lock);
+                        submit_bio(bio->bi_rw, bio);
+                }
+                schedule();
+        }
+        finish_wait(&mddev->sb_wait, &wq);
 }
 
 static int bi_complete(struct bio *bio, unsigned int bytes_done, int error)
@@ -1382,7 +1448,7 @@ static void md_update_sb(mddev_t * mddev)
         int sync_req;
 
 repeat:
-        spin_lock(&mddev->write_lock);
+        spin_lock_irq(&mddev->write_lock);
         sync_req = mddev->in_sync;
         mddev->utime = get_seconds();
         mddev->events ++;
@@ -1405,11 +1471,11 @@ repeat:
          */
         if (!mddev->persistent) {
                 mddev->sb_dirty = 0;
-                spin_unlock(&mddev->write_lock);
+                spin_unlock_irq(&mddev->write_lock);
                 wake_up(&mddev->sb_wait);
                 return;
         }
-        spin_unlock(&mddev->write_lock);
+        spin_unlock_irq(&mddev->write_lock);
 
         dprintk(KERN_INFO 
                 "md: updating %s RAID superblock on device (in sync %d)\n",
@@ -1437,17 +1503,17 @@ repeat:
                         /* only need to write one superblock... */
                         break;
         }
-        wait_event(mddev->sb_wait, atomic_read(&mddev->pending_writes)==0);
+        md_super_wait(mddev);
         /* if there was a failure, sb_dirty was set to 1, and we re-write super */
 
-        spin_lock(&mddev->write_lock);
+        spin_lock_irq(&mddev->write_lock);
         if (mddev->in_sync != sync_req|| mddev->sb_dirty == 1) {
                 /* have to write it out again */
-                spin_unlock(&mddev->write_lock);
+                spin_unlock_irq(&mddev->write_lock);
                 goto repeat;
         }
         mddev->sb_dirty = 0;
-        spin_unlock(&mddev->write_lock);
+        spin_unlock_irq(&mddev->write_lock);
         wake_up(&mddev->sb_wait);
 
 }
@@ -1989,6 +2055,7 @@ static int do_md_run(mddev_t * mddev)
 
         mddev->recovery = 0;
         mddev->resync_max_sectors = mddev->size << 1; /* may be over-ridden by personality */
+        mddev->barriers_work = 1;
 
         /* before we start the array running, initialise the bitmap */
         err = bitmap_create(mddev);
@@ -2107,7 +2174,7 @@ static int do_md_stop(mddev_t * mddev, int ro)
                         mddev->ro = 1;
                 } else {
                         bitmap_flush(mddev);
-                        wait_event(mddev->sb_wait, atomic_read(&mddev->pending_writes)==0);
+                        md_super_wait(mddev);
                         if (mddev->ro)
                                 set_disk_ro(disk, 0);
                         blk_queue_make_request(mddev->queue, md_fail_request);
@@ -3796,13 +3863,13 @@ void md_write_start(mddev_t *mddev, struct bio *bi)
 
         atomic_inc(&mddev->writes_pending);
         if (mddev->in_sync) {
-                spin_lock(&mddev->write_lock);
+                spin_lock_irq(&mddev->write_lock);
                 if (mddev->in_sync) {
                         mddev->in_sync = 0;
                         mddev->sb_dirty = 1;
                         md_wakeup_thread(mddev->thread);
                 }
-                spin_unlock(&mddev->write_lock);
+                spin_unlock_irq(&mddev->write_lock);
         }
         wait_event(mddev->sb_wait, mddev->sb_dirty==0);
 }
@@ -4112,7 +4179,7 @@ void md_check_recovery(mddev_t *mddev)
         if (mddev_trylock(mddev)==0) {
                 int spares =0;
 
-                spin_lock(&mddev->write_lock);
+                spin_lock_irq(&mddev->write_lock);
                 if (mddev->safemode && !atomic_read(&mddev->writes_pending) &&
                     !mddev->in_sync && mddev->recovery_cp == MaxSector) {
                         mddev->in_sync = 1;
@@ -4120,7 +4187,7 @@ void md_check_recovery(mddev_t *mddev)
                 }
                 if (mddev->safemode == 1)
                         mddev->safemode = 0;
-                spin_unlock(&mddev->write_lock);
+                spin_unlock_irq(&mddev->write_lock);
 
                 if (mddev->sb_dirty)
                         md_update_sb(mddev);