raid5: fix 2 bugs in ops_complete_biofill

1/ ops_complete_biofill tried to avoid calling handle_stripe since all the
state necessary to return read completions is available.  However the
process of determining whether more read requests are pending requires
locking the stripe (to block add_stripe_bio from updating dev->toead).
ops_complete_biofill can run in tasklet context, so rather than upgrading
all the stripe locks from spin_lock to spin_lock_bh this patch just
unconditionally reschedules handle_stripe after completing the read
request.

2/ ops_complete_biofill needlessly qualified processing R5_Wantfill with
dev->toread.  The result being that the 'biofill' pending bit is cleared
before handling the pending read-completions on dev->read.  R5_Wantfill can
be unconditionally handled because the 'biofill' pending bit prevents new
R5_Wantfill requests from being seen by ops_run_biofill and
ops_complete_biofill.

Found-by: Yuri Tikhonov <yur@emcraft.com>
[neilb@suse.de: simpler fix for bug 1 than moving code]
Signed-off-by: NeilBrown <neilb@suse.de>
Signed-off-by: Dan Williams <dan.j.williams@intel.com>

1 files changed, 7 insertions, 10 deletions

diff --git a/drivers/md/raid5.c b/drivers/md/raid5.c
index 4d63773ee73a..f96dea975fa5 100644
--- a/drivers/md/raid5.c
+++ b/drivers/md/raid5.c
@@ -514,7 +514,7 @@ static void ops_complete_biofill(void *stripe_head_ref)
         struct stripe_head *sh = stripe_head_ref;
         struct bio *return_bi = NULL;
         raid5_conf_t *conf = sh->raid_conf;
-        int i, more_to_read = 0;
+        int i;
 
         pr_debug("%s: stripe %llu\n", __FUNCTION__,
                 (unsigned long long)sh->sector);
@@ -522,16 +522,14 @@ static void ops_complete_biofill(void *stripe_head_ref)
         /* clear completed biofills */
         for (i = sh->disks; i--; ) {
                 struct r5dev *dev = &sh->dev[i];
-                /* check if this stripe has new incoming reads */
-                if (dev->toread)
-                        more_to_read++;
 
                 /* acknowledge completion of a biofill operation */
-                /* and check if we need to reply to a read request
-                */
-                if (test_bit(R5_Wantfill, &dev->flags) && !dev->toread) {
+                /* and check if we need to reply to a read request,
+                 * new R5_Wantfill requests are held off until
+                 * !test_bit(STRIPE_OP_BIOFILL, &sh->ops.pending)
+                 */
+                if (test_and_clear_bit(R5_Wantfill, &dev->flags)) {
                         struct bio *rbi, *rbi2;
-                        clear_bit(R5_Wantfill, &dev->flags);
 
                         /* The access to dev->read is outside of the
                          * spin_lock_irq(&conf->device_lock), but is protected
@@ -558,8 +556,7 @@ static void ops_complete_biofill(void *stripe_head_ref)
 
         return_io(return_bi);
 
-        if (more_to_read)
-                set_bit(STRIPE_HANDLE, &sh->state);
+        set_bit(STRIPE_HANDLE, &sh->state);
         release_stripe(sh);
 }