[PATCH] md: fix up some rdev rcu locking in raid5/6

There is this "FIXME" comment with a typo in it!!  that been annoying me for
days, so I just had to remove it.

conf->disks[i].rdev should only be accessed if
  - we know we hold a reference or
  - the mddev->reconfig_sem is down or
  - we have a rcu_readlock

handle_stripe was referencing rdev in three places without any of these.  For
the first two, get an rcu_readlock.  For the last, the same access
(md_sync_acct call) is made a little later after the rdev has been claimed
under and rcu_readlock, if R5_Syncio is set.  So just use that access...
However R5_Syncio isn't really needed as the 'syncing' variable contains the
same information.  So use that instead.

Issues, comment, and fix are identical in raid5 and raid6.

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, 8 insertions, 11 deletions

diff --git a/drivers/md/raid6main.c b/drivers/md/raid6main.c
index 7a51553d8be..b5b7a8d0b16 100644
--- a/drivers/md/raid6main.c
+++ b/drivers/md/raid6main.c
@@ -1060,11 +1060,11 @@ static void handle_stripe(struct stripe_head *sh, struct page *tmp_page)
         syncing = test_bit(STRIPE_SYNCING, &sh->state);
         /* Now to look around and see what can be done */
 
+        rcu_read_lock();
         for (i=disks; i--; ) {
                 mdk_rdev_t *rdev;
                 dev = &sh->dev[i];
                 clear_bit(R5_Insync, &dev->flags);
-                clear_bit(R5_Syncio, &dev->flags);
 
                 PRINTK("check %d: state 0x%lx read %p write %p written %p\n",
                         i, dev->flags, dev->toread, dev->towrite, dev->written);
@@ -1103,7 +1103,7 @@ static void handle_stripe(struct stripe_head *sh, struct page *tmp_page)
                                 non_overwrite++;
                 }
                 if (dev->written) written++;
-                rdev = conf->disks[i].rdev; /* FIXME, should I be looking rdev */
+                rdev = rcu_dereference(conf->disks[i].rdev);
                 if (!rdev || !test_bit(In_sync, &rdev->flags)) {
                         /* The ReadError flag will just be confusing now */
                         clear_bit(R5_ReadError, &dev->flags);
@@ -1117,6 +1117,7 @@ static void handle_stripe(struct stripe_head *sh, struct page *tmp_page)
                 } else
                         set_bit(R5_Insync, &dev->flags);
         }
+        rcu_read_unlock();
         PRINTK("locked=%d uptodate=%d to_read=%d"
                " to_write=%d failed=%d failed_num=%d,%d\n",
                locked, uptodate, to_read, to_write, failed,
@@ -1129,10 +1130,13 @@ static void handle_stripe(struct stripe_head *sh, struct page *tmp_page)
                         int bitmap_end = 0;
 
                         if (test_bit(R5_ReadError, &sh->dev[i].flags)) {
-                                mdk_rdev_t *rdev = conf->disks[i].rdev;
+                                mdk_rdev_t *rdev;
+                                rcu_read_lock();
+                                rdev = rcu_dereference(conf->disks[i].rdev);
                                 if (rdev && test_bit(In_sync, &rdev->flags))
                                         /* multiple read failures in one stripe */
                                         md_error(conf->mddev, rdev);
+                                rcu_read_unlock();
                         }
 
                         spin_lock_irq(&conf->device_lock);
@@ -1307,9 +1311,6 @@ static void handle_stripe(struct stripe_head *sh, struct page *tmp_page)
                                         locked++;
                                         PRINTK("Reading block %d (sync=%d)\n",
                                                 i, syncing);
-                                        if (syncing)
-                                                md_sync_acct(conf->disks[i].rdev->bdev,
-                                                             STRIPE_SECTORS);
                                 }
                         }
                 }
@@ -1463,14 +1464,12 @@ static void handle_stripe(struct stripe_head *sh, struct page *tmp_page)
                                 locked++;
                                 set_bit(R5_LOCKED, &dev->flags);
                                 set_bit(R5_Wantwrite, &dev->flags);
-                                set_bit(R5_Syncio, &dev->flags);
                         }
                         if (failed >= 1) {
                                 dev = &sh->dev[failed_num[0]];
                                 locked++;
                                 set_bit(R5_LOCKED, &dev->flags);
                                 set_bit(R5_Wantwrite, &dev->flags);
-                                set_bit(R5_Syncio, &dev->flags);
                         }
 
                         if (update_p) {
@@ -1478,14 +1477,12 @@ static void handle_stripe(struct stripe_head *sh, struct page *tmp_page)
                                 locked ++;
                                 set_bit(R5_LOCKED, &dev->flags);
                                 set_bit(R5_Wantwrite, &dev->flags);
-                                set_bit(R5_Syncio, &dev->flags);
                         }
                         if (update_q) {
                                 dev = &sh->dev[qd_idx];
                                 locked++;
                                 set_bit(R5_LOCKED, &dev->flags);
                                 set_bit(R5_Wantwrite, &dev->flags);
-                                set_bit(R5_Syncio, &dev->flags);
                         }
                         clear_bit(STRIPE_DEGRADED, &sh->state);
 
@@ -1557,7 +1554,7 @@ static void handle_stripe(struct stripe_head *sh, struct page *tmp_page)
                 rcu_read_unlock();
 
                 if (rdev) {
-                        if (test_bit(R5_Syncio, &sh->dev[i].flags))
+                        if (syncing)
                                 md_sync_acct(rdev->bdev, STRIPE_SECTORS);
 
                         bi->bi_bdev = rdev->bdev;