dm mpath: add retry pg init

This patch allows a failed path group initialisation command to be retried.

It adds a generic MP_RETRY flag and a "pg_init_retries" feature to
device-mapper multipath which limits the number of retries.

1. A hw handler sends a path initialization command to the storage and
the command completes with an error code indicating the command
should be retried.

2. The hardware handler calls dm_pg_init_complete() with MP_RETRY
set in err_flags to ask the dm multipath core to retry.

3. If the retry limit has not been exceeded, pg_init() is retried.
Otherwise fail_path() is called.

If you are using the userspace multipath-tools or device-mapper-multipath
package, you can set pg_init_retries in the 'device' section of your
/etc/multipath.conf file. For example:

features                "2 pg_init_retries 7"

The number of PG retries attempted is reported in the 'dmsetup status' output.

Signed-off-by: Dave Wysochanski <dwysocha@redhat.com>
Acked-by: Mike Christie <michaelc@cs.wisc.edu>
Acked-by: Chandra Seetharaman <sekharan@us.ibm.com>
Signed-off-by: Alasdair G Kergon <agk@redhat.com>

2 files changed, 68 insertions, 14 deletions

diff --git a/drivers/md/dm-hw-handler.h b/drivers/md/dm-hw-handler.h
index e0832e6fcf36..46809dcb121a 100644
--- a/drivers/md/dm-hw-handler.h
+++ b/drivers/md/dm-hw-handler.h
@@ -58,5 +58,6 @@ unsigned dm_scsi_err_handler(struct hw_handler *hwh, struct bio *bio);
 #define MP_FAIL_PATH 1
 #define MP_BYPASS_PG 2
 #define MP_ERROR_IO  4  /* Don't retry this I/O */
+#define MP_RETRY 8
 
 #endif
diff --git a/drivers/md/dm-mpath.c b/drivers/md/dm-mpath.c
index 31056abca89d..dd5ad6310f54 100644
--- a/drivers/md/dm-mpath.c
+++ b/drivers/md/dm-mpath.c
@@ -75,6 +75,8 @@ struct multipath {
         unsigned queue_io;              /* Must we queue all I/O? */
         unsigned queue_if_no_path;      /* Queue I/O if last path fails? */
         unsigned saved_queue_if_no_path;/* Saved state during suspension */
+        unsigned pg_init_retries;       /* Number of times to retry pg_init */
+        unsigned pg_init_count;         /* Number of times pg_init called */
 
         struct work_struct process_queued_ios;
         struct bio_list queued_ios;
@@ -225,6 +227,8 @@ static void __switch_pg(struct multipath *m, struct pgpath *pgpath)
                 m->pg_init_required = 0;
                 m->queue_io = 0;
         }
+
+        m->pg_init_count = 0;
 }
 
 static int __choose_path_in_pg(struct multipath *m, struct priority_group *pg)
@@ -424,6 +428,7 @@ static void process_queued_ios(struct work_struct *work)
                 must_queue = 0;
 
         if (m->pg_init_required && !m->pg_init_in_progress) {
+                m->pg_init_count++;
                 m->pg_init_required = 0;
                 m->pg_init_in_progress = 1;
                 init_required = 1;
@@ -689,9 +694,11 @@ static int parse_features(struct arg_set *as, struct multipath *m)
         int r;
         unsigned argc;
         struct dm_target *ti = m->ti;
+        const char *param_name;
 
         static struct param _params[] = {
-                {0, 1, "invalid number of feature args"},
+                {0, 3, "invalid number of feature args"},
+                {1, 50, "pg_init_retries must be between 1 and 50"},
         };
 
         r = read_param(_params, shift(as), &argc, &ti->error);
@@ -701,12 +708,28 @@ static int parse_features(struct arg_set *as, struct multipath *m)
         if (!argc)
                 return 0;
 
-        if (!strnicmp(shift(as), MESG_STR("queue_if_no_path")))
-                return queue_if_no_path(m, 1, 0);
-        else {
+        do {
+                param_name = shift(as);
+                argc--;
+
+                if (!strnicmp(param_name, MESG_STR("queue_if_no_path"))) {
+                        r = queue_if_no_path(m, 1, 0);
+                        continue;
+                }
+
+                if (!strnicmp(param_name, MESG_STR("pg_init_retries")) &&
+                    (argc >= 1)) {
+                        r = read_param(_params + 1, shift(as),
+                                       &m->pg_init_retries, &ti->error);
+                        argc--;
+                        continue;
+                }
+
                 ti->error = "Unrecognised multipath feature request";
-                return -EINVAL;
-        }
+                r = -EINVAL;
+        } while (argc && !r);
+
+        return r;
 }
 
 static int multipath_ctr(struct dm_target *ti, unsigned int argc,
@@ -976,6 +999,26 @@ static int bypass_pg_num(struct multipath *m, const char *pgstr, int bypassed)
 }
 
 /*
+ * Should we retry pg_init immediately?
+ */
+static int pg_init_limit_reached(struct multipath *m, struct pgpath *pgpath)
+{
+        unsigned long flags;
+        int limit_reached = 0;
+
+        spin_lock_irqsave(&m->lock, flags);
+
+        if (m->pg_init_count <= m->pg_init_retries)
+                m->pg_init_required = 1;
+        else
+                limit_reached = 1;
+
+        spin_unlock_irqrestore(&m->lock, flags);
+
+        return limit_reached;
+}
+
+/*
  * pg_init must call this when it has completed its initialisation
  */
 void dm_pg_init_complete(struct dm_path *path, unsigned err_flags)
@@ -985,8 +1028,14 @@ void dm_pg_init_complete(struct dm_path *path, unsigned err_flags)
         struct multipath *m = pg->m;
         unsigned long flags;
 
-        /* We insist on failing the path if the PG is already bypassed. */
-        if (err_flags && pg->bypassed)
+        /*
+         * If requested, retry pg_init until maximum number of retries exceeded.
+         * If retry not requested and PG already bypassed, always fail the path.
+         */
+        if (err_flags & MP_RETRY) {
+                if (pg_init_limit_reached(m, pgpath))
+                        err_flags |= MP_FAIL_PATH;
+        } else if (err_flags && pg->bypassed)
                 err_flags |= MP_FAIL_PATH;
 
         if (err_flags & MP_FAIL_PATH)
@@ -996,7 +1045,7 @@ void dm_pg_init_complete(struct dm_path *path, unsigned err_flags)
                 bypass_pg(m, pg, 1);
 
         spin_lock_irqsave(&m->lock, flags);
-        if (err_flags) {
+        if (err_flags & ~MP_RETRY) {
                 m->current_pgpath = NULL;
                 m->current_pg = NULL;
         } else if (!m->pg_init_required)
@@ -1148,11 +1197,15 @@ static int multipath_status(struct dm_target *ti, status_type_t type,
 
         /* Features */
         if (type == STATUSTYPE_INFO)
-                DMEMIT("1 %u ", m->queue_size);
-        else if (m->queue_if_no_path)
-                DMEMIT("1 queue_if_no_path ");
-        else
-                DMEMIT("0 ");
+                DMEMIT("2 %u %u ", m->queue_size, m->pg_init_count);
+        else {
+                DMEMIT("%u ", m->queue_if_no_path +
+                              (m->pg_init_retries > 0) * 2);
+                if (m->queue_if_no_path)
+                        DMEMIT("queue_if_no_path ");
+                if (m->pg_init_retries)
+                        DMEMIT("pg_init_retries %u ", m->pg_init_retries);
+        }
 
         if (hwh->type && hwh->type->status)
                 sz += hwh->type->status(hwh, type, result + sz, maxlen - sz);