[PATCH 4.2.y-ckt 051/218] RAID5: check_reshape() shouldn't call mddev_suspend

[Kamal Mostafa]

4.2.8-ckt7 -stable review patch.  If anyone has any objections, please let me 
know.

---8<------------------------------------------------------------

From: Shaohua Li <s...@fb.com>

commit 27a353c026a879a1001e5eac4bda75b16262c44a upstream.

check_reshape() is called from raid5d thread. raid5d thread shouldn't
call mddev_suspend(), because mddev_suspend() waits for all IO finish
but IO is handled in raid5d thread, we could easily deadlock here.

This issue is introduced by
738a273 ("md/raid5: fix allocation of 'scribble' array.")

Reported-and-tested-by: Artur Paszkiewicz <artur.paszkiew...@intel.com>
Reviewed-by: NeilBrown <ne...@suse.com>
Signed-off-by: Shaohua Li <s...@fb.com>
Signed-off-by: Kamal Mostafa <ka...@canonical.com>
---
 drivers/md/raid5.c | 18 ++++++++++++++++++
 drivers/md/raid5.h |  2 ++
 2 files changed, 20 insertions(+)

diff --git a/drivers/md/raid5.c b/drivers/md/raid5.c
index a6917f0..a55b6859 100644
--- a/drivers/md/raid5.c
+++ b/drivers/md/raid5.c
@@ -2091,6 +2091,14 @@ static int resize_chunks(struct r5conf *conf, int 
new_disks, int new_sectors)
        unsigned long cpu;
        int err = 0;
 
+       /*
+        * Never shrink. And mddev_suspend() could deadlock if this is called
+        * from raid5d. In that case, scribble_disks and scribble_sectors
+        * should equal to new_disks and new_sectors
+        */
+       if (conf->scribble_disks >= new_disks &&
+           conf->scribble_sectors >= new_sectors)
+               return 0;
        mddev_suspend(conf->mddev);
        get_online_cpus();
        for_each_present_cpu(cpu) {
@@ -2112,6 +2120,10 @@ static int resize_chunks(struct r5conf *conf, int 
new_disks, int new_sectors)
        }
        put_online_cpus();
        mddev_resume(conf->mddev);
+       if (!err) {
+               conf->scribble_disks = new_disks;
+               conf->scribble_sectors = new_sectors;
+       }
        return err;
 }
 
@@ -6379,6 +6391,12 @@ static int raid5_alloc_percpu(struct r5conf *conf)
        }
        put_online_cpus();
 
+       if (!err) {
+               conf->scribble_disks = max(conf->raid_disks,
+                       conf->previous_raid_disks);
+               conf->scribble_sectors = max(conf->chunk_sectors,
+                       conf->prev_chunk_sectors);
+       }
        return err;
 }
 
diff --git a/drivers/md/raid5.h b/drivers/md/raid5.h
index d051442..65ecd49 100644
--- a/drivers/md/raid5.h
+++ b/drivers/md/raid5.h
@@ -501,6 +501,8 @@ struct r5conf {
                                              * conversions
                                              */
        } __percpu *percpu;
+       int scribble_disks;
+       int scribble_sectors;
 #ifdef CONFIG_HOTPLUG_CPU
        struct notifier_block   cpu_notify;
 #endif
-- 
2.7.4