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Subject[2.6.24 PATCH 21/25] dm mpath: add retry pg init
From: Dave Wysochanski <dwysocha@redhat.com>

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>

---
[AGK TODO: Perform a fresh review of the state machine changes related to dm_pg_init_complete.]

drivers/md/dm-hw-handler.h | 1
drivers/md/dm-mpath.c | 81 +++++++++++++++++++++++++++++++++++++--------
2 files changed, 68 insertions(+), 14 deletions(-)
Index: linux-2.6.23/drivers/md/dm-hw-handler.h
===================================================================
--- linux-2.6.23.orig/drivers/md/dm-hw-handler.h 2007-10-12 12:36:14.000000000 +0100
+++ linux-2.6.23/drivers/md/dm-hw-handler.h 2007-10-12 15:03:28.000000000 +0100
@@ -58,5 +58,6 @@ unsigned dm_scsi_err_handler(struct hw_h
#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
Index: linux-2.6.23/drivers/md/dm-mpath.c
===================================================================
--- linux-2.6.23.orig/drivers/md/dm-mpath.c 2007-10-12 13:14:40.000000000 +0100
+++ linux-2.6.23/drivers/md/dm-mpath.c 2007-10-12 15:03:28.000000000 +0100
@@ -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->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 wo
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
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
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 multipat
}

/*
+ * 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
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
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_ta

/* 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);
-
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