[4.2.y-ckt stable] Patch "RAID5: check_reshape() shouldn't call mddev_suspend" has been added to the 4.2.y-ckt tree

[Kamal Mostafa]

This is a note to let you know that I have just added a patch titled

    RAID5: check_reshape() shouldn't call mddev_suspend

to the linux-4.2.y-queue branch of the 4.2.y-ckt extended stable tree 
which can be found at:

    http://kernel.ubuntu.com/git/ubuntu/linux.git/log/?h=linux-4.2.y-queue

This patch is scheduled to be released in version 4.2.8-ckt7.

If you, or anyone else, feels it should not be added to this tree, please 
reply to this email.

For more information about the 4.2.y-ckt tree, see
https://wiki.ubuntu.com/Kernel/Dev/ExtendedStable

Thanks.
-Kamal

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

>From 625af781568daba5a11d6c7676e4dd237f7774e0 Mon Sep 17 00:00:00 2001
From: Shaohua Li <shli at fb.com>
Date: Wed, 24 Feb 2016 17:38:28 -0800
Subject: RAID5: check_reshape() shouldn't call mddev_suspend

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.paszkiewicz at intel.com>
Reviewed-by: NeilBrown <neilb at suse.com>
Signed-off-by: Shaohua Li <shli at fb.com>
Signed-off-by: Kamal Mostafa <kamal at 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