raid5: fix unending write sequence

<debug output from Joel's system>
handling stripe 7629696, state=0x14 cnt=1, pd_idx=2 ops=0:0:0
check 5: state 0x6 toread 0000000000000000 read 0000000000000000 write fffff800ffcffcc0 written 0000000000000000
check 4: state 0x6 toread 0000000000000000 read 0000000000000000 write fffff800fdd4e360 written 0000000000000000
check 3: state 0x1 toread 0000000000000000 read 0000000000000000 write 0000000000000000 written 0000000000000000
check 2: state 0x1 toread 0000000000000000 read 0000000000000000 write 0000000000000000 written 0000000000000000
check 1: state 0x6 toread 0000000000000000 read 0000000000000000 write fffff800ff517e40 written 0000000000000000
check 0: state 0x6 toread 0000000000000000 read 0000000000000000 write fffff800fd4cae60 written 0000000000000000
locked=4 uptodate=2 to_read=0 to_write=4 failed=0 failed_num=0
for sector 7629696, rmw=0 rcw=0
</debug>

These blocks were prepared to be written out, but were never handled in
ops_run_biodrain(), so they remain locked forever.  The operations flags
are all clear which means handle_stripe() thinks nothing else needs to be
done.

This state suggests that the STRIPE_OP_PREXOR bit was sampled 'set' when it
should not have been.  This patch cleans up cases where the code looks at
sh->ops.pending when it should be looking at the consistent stack-based
snapshot of the operations flags.

Report from Joel:
	Resync done. Patch fix this bug.

Signed-off-by: Dan Williams <dan.j.williams@intel.com>
Tested-by: Joel Bertrand <joel.bertrand@systella.fr>
Cc: <stable@kernel.org>
Cc: Neil Brown <neilb@suse.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 9 insertions, 7 deletions

diff --git a/drivers/md/raid5.c b/drivers/md/raid5.c
index 1cfc984cc7b7..a5aad8cad843 100644
--- a/drivers/md/raid5.c
+++ b/drivers/md/raid5.c
@@ -688,7 +688,8 @@ ops_run_prexor(struct stripe_head *sh, struct dma_async_tx_descriptor *tx)
 }
 
 static struct dma_async_tx_descriptor *
-ops_run_biodrain(struct stripe_head *sh, struct dma_async_tx_descriptor *tx)
+ops_run_biodrain(struct stripe_head *sh, struct dma_async_tx_descriptor *tx,
+                 unsigned long pending)
 {
         int disks = sh->disks;
         int pd_idx = sh->pd_idx, i;
@@ -696,7 +697,7 @@ ops_run_biodrain(struct stripe_head *sh, struct dma_async_tx_descriptor *tx)
         /* check if prexor is active which means only process blocks
          * that are part of a read-modify-write (Wantprexor)
          */
-        int prexor = test_bit(STRIPE_OP_PREXOR, &sh->ops.pending);
+        int prexor = test_bit(STRIPE_OP_PREXOR, &pending);
 
         pr_debug("%s: stripe %llu\n", __FUNCTION__,
                 (unsigned long long)sh->sector);
@@ -773,7 +774,8 @@ static void ops_complete_write(void *stripe_head_ref)
 }
 
 static void
-ops_run_postxor(struct stripe_head *sh, struct dma_async_tx_descriptor *tx)
+ops_run_postxor(struct stripe_head *sh, struct dma_async_tx_descriptor *tx,
+                unsigned long pending)
 {
         /* kernel stack size limits the total number of disks */
         int disks = sh->disks;
@@ -781,7 +783,7 @@ ops_run_postxor(struct stripe_head *sh, struct dma_async_tx_descriptor *tx)
 
         int count = 0, pd_idx = sh->pd_idx, i;
         struct page *xor_dest;
-        int prexor = test_bit(STRIPE_OP_PREXOR, &sh->ops.pending);
+        int prexor = test_bit(STRIPE_OP_PREXOR, &pending);
         unsigned long flags;
         dma_async_tx_callback callback;
 
@@ -808,7 +810,7 @@ ops_run_postxor(struct stripe_head *sh, struct dma_async_tx_descriptor *tx)
         }
 
         /* check whether this postxor is part of a write */
-        callback = test_bit(STRIPE_OP_BIODRAIN, &sh->ops.pending) ?
+        callback = test_bit(STRIPE_OP_BIODRAIN, &pending) ?
                 ops_complete_write : ops_complete_postxor;
 
         /* 1/ if we prexor'd then the dest is reused as a source
@@ -896,12 +898,12 @@ static void raid5_run_ops(struct stripe_head *sh, unsigned long pending)
                 tx = ops_run_prexor(sh, tx);
 
         if (test_bit(STRIPE_OP_BIODRAIN, &pending)) {
-                tx = ops_run_biodrain(sh, tx);
+                tx = ops_run_biodrain(sh, tx, pending);
                 overlap_clear++;
         }
 
         if (test_bit(STRIPE_OP_POSTXOR, &pending))
-                ops_run_postxor(sh, tx);
+                ops_run_postxor(sh, tx, pending);
 
         if (test_bit(STRIPE_OP_CHECK, &pending))
                 ops_run_check(sh);