md: Ensure no IO request to get md device before it is properly initialised.

When an md device is in the process of coming on line it is possible
for an IO request (typically a partition table probe) to get through
before the array is fully initialised, which can cause unexpected
behaviour (e.g. a crash).

So explicitly record when the array is ready for IO and don't allow IO
through until then.

There is no possibility for a similar problem when the array is going
off-line as there must only be one 'open' at that time, and it is busy
off-lining the array and so cannot send IO requests.  So no memory
barrier is needed in md_stop()

This has been a bug since commit 409c57f3801 in 2.6.30 which
introduced md_make_request.  Before then, each personality would
register its own make_request_fn when it was ready.
This is suitable for any stable kernel from 2.6.30.y onwards.

Cc: <stable@kernel.org>
Signed-off-by: NeilBrown <neilb@suse.de>
Reported-by:  "Hawrylewicz Czarnowski, Przemyslaw" <przemyslaw.hawrylewicz.czarnowski@intel.com>

diff --git a/drivers/md/md.c b/drivers/md/md.c
index a3019121dc574012615e1c2be428fb5bf2e530c6..540347c538f95d86f0fae000520e50c18db70cd8 100644 (file)
--- a/drivers/md/md.c
+++ b/drivers/md/md.c
@@ -288,10 +288,12 @@ static int md_make_request(struct request_queue *q, struct bio *bio)
        int rv;
        int cpu;
 
-       if (mddev == NULL || mddev->pers == NULL) {
+       if (mddev == NULL || mddev->pers == NULL
+           || !mddev->ready) {
                bio_io_error(bio);
                return 0;
        }
+       smp_rmb(); /* Ensure implications of  'active' are visible */
        rcu_read_lock();
        if (mddev->suspended) {
                DEFINE_WAIT(__wait);
@@ -4564,7 +4566,8 @@ int md_run(mddev_t *mddev)
        mddev->safemode_timer.data = (unsigned long) mddev;
        mddev->safemode_delay = (200 * HZ)/1000 +1; /* 200 msec delay */
        mddev->in_sync = 1;
-
+       smp_wmb();
+       mddev->ready = 1;
        list_for_each_entry(rdev, &mddev->disks, same_set)
                if (rdev->raid_disk >= 0) {
                        char nm[20];
@@ -4725,6 +4728,7 @@ EXPORT_SYMBOL_GPL(md_stop_writes);
 
 void md_stop(mddev_t *mddev)
 {
+       mddev->ready = 0;
        mddev->pers->stop(mddev);
        if (mddev->pers->sync_request && mddev->to_remove == NULL)
                mddev->to_remove = &md_redundancy_group;

diff --git a/drivers/md/md.h b/drivers/md/md.h
index d05bab55df4e7d3b49a500ad196610bfd1d2e67c..229675a604f7766468a67c480591c45613370241 100644 (file)
--- a/drivers/md/md.h
+++ b/drivers/md/md.h
@@ -148,7 +148,8 @@ struct mddev_s
                                                       * are happening, so run/
                                                       * takeover/stop are not safe
                                                       */
-
+       int                             ready; /* See when safe to pass 
+                                               * IO requests down */
        struct gendisk                  *gendisk;
 
        struct kobject                  kobj;