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Subject[217/272] md: Ensure no IO request to get md device before it is properly initialised.
2.6.37-stable review patch.  If anyone has any objections, please let us know.

------------------
From: NeilBrown <neilb@suse.de>

commit 0ca69886a8273ac1350143d562280bfcbe4760dc upstream.

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.

Signed-off-by: NeilBrown <neilb@suse.de>
Reported-by: "Hawrylewicz Czarnowski, Przemyslaw" <przemyslaw.hawrylewicz.czarnowski@intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

---
drivers/md/md.c | 8 ++++++--
drivers/md/md.h | 3 ++-
2 files changed, 8 insertions(+), 3 deletions(-)
--- a/drivers/md/md.c
+++ b/drivers/md/md.c
@@ -288,10 +288,12 @@ static int md_make_request(struct reques
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;
--- 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;



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