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>

diff --git a/drivers/md/raid5.c b/drivers/md/raid5.c
index 4d63773ee73a634fe31d72eb04edad4d8942f8e2..f96dea975fa50d94e805c40c46be82df7cfe80bc 100644 (file)
--- 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);
 }