Patch "zswap: don't param_set_charp while holding spinlock" has been added to the 4.4-stable tree

This is a note to let you know that I've just added the patch titled

    zswap: don't param_set_charp while holding spinlock

to the 4.4-stable tree which can be found at:
    http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
     zswap-don-t-param_set_charp-while-holding-spinlock.patch
and it can be found in the queue-4.4 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let [off-list ref] know about it.

From fd5bb66cd934987e49557455b6497fc006521940 Mon Sep 17 00:00:00 2001

From: Dan Streetman <redacted>
Date: Mon, 27 Feb 2017 14:26:53 -0800
Subject: zswap: don't param_set_charp while holding spinlock

From: Dan Streetman <redacted>

commit fd5bb66cd934987e49557455b6497fc006521940 upstream.

Change the zpool/compressor param callback function to release the
zswap_pools_lock spinlock before calling param_set_charp, since that
function may sleep when it calls kmalloc with GFP_KERNEL.

While this problem has existed for a while, I wasn't able to trigger it
using a tight loop changing either/both the zpool and compressor params; I
think it's very unlikely to be an issue on the stable kernels, especially
since most zswap users will change the compressor and/or zpool from sysfs
only one time each boot - or zero times, if they add the params to the
kernel boot.

Fixes: c99b42c3529e ("zswap: use charp for zswap param strings")
Link: http://lkml.kernel.org/r/20170126155821.4545-1-ddstreet@ieee.org
Signed-off-by: Dan Streetman <redacted>
Reported-by: Sergey Senozhatsky <redacted>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: Minchan Kim <minchan@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Vlastimil Babka <redacted>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
 mm/zswap.c |   12 ++++++++----
 1 file changed, 8 insertions(+), 4 deletions(-)

--- a/mm/zswap.c
+++ b/mm/zswap.c

@@ -752,18 +752,22 @@ static int __zswap_param_set(const char
 	pool = zswap_pool_find_get(type, compressor);
 	if (pool) {
 		zswap_pool_debug("using existing", pool);
+		WARN_ON(pool == zswap_pool_current());
 		list_del_rcu(&pool->list);
-	} else {
-		spin_unlock(&zswap_pools_lock);
-		pool = zswap_pool_create(type, compressor);
-		spin_lock(&zswap_pools_lock);
 	}
 
+	spin_unlock(&zswap_pools_lock);
+
+	if (!pool)
+		pool = zswap_pool_create(type, compressor);
+
 	if (pool)
 		ret = param_set_charp(s, kp);
 	else
 		ret = -EINVAL;
 
+	spin_lock(&zswap_pools_lock);
+
 	if (!ret) {
 		put_pool = zswap_pool_current();
 		list_add_rcu(&pool->list, &zswap_pools);

Patches currently in stable-queue which might be from ddstreet@ieee.org are

queue-4.4/mm-zswap-use-workqueue-to-destroy-pool.patch
queue-4.4/zswap-don-t-param_set_charp-while-holding-spinlock.patch