md: replace STRIPE_OP_CHECK with 'check_states'

From: Dan Williams <dan.j.williams@intel.com>

The STRIPE_OP_* flags record the state of stripe operations which are
performed outside the stripe lock.  Their use in indicating which
operations need to be run is straightforward; however, interpolating what
the next state of the stripe should be based on a given combination of
these flags is not straightforward, and has led to bugs.  An easier to read
implementation with minimal degrees of freedom is needed.

Towards this goal, this patch introduces explicit states to replace what was
previously interpolated from the STRIPE_OP_* flags.  For now this only converts
the handle_parity_checks5 path, removing a user of the
ops.{pending,ack,complete,count} fields of struct stripe_operations.

This conversion also found a remaining issue with the current code.  There is
a small window for a drive to fail between when we schedule a repair and when
the parity calculation for that repair completes.  When this happens we will
writeback to 'failed_num' when we really want to write back to 'pd_idx'.

Signed-off-by: Dan Williams <dan.j.williams@intel.com>
Signed-off-by: Neil Brown <neilb@suse.de>

1 files changed, 40 insertions, 6 deletions

diff --git a/include/linux/raid/raid5.h b/include/linux/raid/raid5.h
index 1301195abf4b..2c96d5fd54bf 100644
--- a/include/linux/raid/raid5.h
+++ b/include/linux/raid/raid5.h
@@ -158,6 +158,41 @@
  *    the compute block completes.
  */
 
+/*
+ * Operations state - intermediate states that are visible outside of sh->lock
+ * In general _idle indicates nothing is running, _run indicates a data
+ * processing operation is active, and _result means the data processing result
+ * is stable and can be acted upon.  For simple operations like biofill and
+ * compute that only have an _idle and _run state they are indicated with
+ * sh->state flags (STRIPE_BIOFILL_RUN and STRIPE_COMPUTE_RUN)
+ */
+/**
+ * enum check_states - handles syncing / repairing a stripe
+ * @check_state_idle - check operations are quiesced
+ * @check_state_run - check operation is running
+ * @check_state_result - set outside lock when check result is valid
+ * @check_state_compute_run - check failed and we are repairing
+ * @check_state_compute_result - set outside lock when compute result is valid
+ */
+enum check_states {
+        check_state_idle = 0,
+        check_state_run, /* parity check */
+        check_state_check_result,
+        check_state_compute_run, /* parity repair */
+        check_state_compute_result,
+};
+
+/**
+ * enum reconstruct_states - handles writing or expanding a stripe
+ */
+enum reconstruct_states {
+        reconstruct_state_idle = 0,
+        reconstruct_state_drain_run,            /* write */
+        reconstruct_state_run,                  /* expand */
+        reconstruct_state_drain_result,
+        reconstruct_state_result,
+};
+
 struct stripe_head {
         struct hlist_node       hash;
         struct list_head        lru;                    /* inactive_list or handle_list */
@@ -169,6 +204,7 @@ struct stripe_head {
         spinlock_t              lock;
         int                     bm_seq; /* sequence number for bitmap flushes */
         int                     disks;                  /* disks in stripe */
+        enum check_states       check_state;
         /* stripe_operations
          * @pending - pending ops flags (set for request->issue->complete)
          * @ack - submitted ops flags (set for issue->complete)
@@ -202,6 +238,7 @@ struct stripe_head_state {
         int locked, uptodate, to_read, to_write, failed, written;
         int to_fill, compute, req_compute, non_overwrite;
         int failed_num;
+        unsigned long ops_request;
 };
 
 /* r6_state - extra state data only relevant to r6 */
@@ -254,8 +291,10 @@ struct r6_state {
 #define STRIPE_EXPAND_READY     11
 #define STRIPE_IO_STARTED       12 /* do not count towards 'bypass_count' */
 #define STRIPE_FULL_WRITE       13 /* all blocks are set to be overwritten */
+#define STRIPE_BIOFILL_RUN      14
+#define STRIPE_COMPUTE_RUN      15
 /*
- * Operations flags (in issue order)
+ * Operation request flags
  */
 #define STRIPE_OP_BIOFILL       0
 #define STRIPE_OP_COMPUTE_BLK   1
@@ -264,11 +303,6 @@ struct r6_state {
 #define STRIPE_OP_POSTXOR       4
 #define STRIPE_OP_CHECK 5
 
-/* modifiers to the base operations
- * STRIPE_OP_MOD_REPAIR_PD - compute the parity block and write it back
- */
-#define STRIPE_OP_MOD_REPAIR_PD 7
-
 /*
  * Plugging:
  *