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 4.9-stable tree which can be found at: http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git%3Ba=su...

The filename of the patch is: zswap-don-t-param_set_charp-while-holding-spinlock.patch and it can be found in the queue-4.9 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let stable@vger.kernel.org know about it.

From fd5bb66cd934987e49557455b6497fc006521940 Mon Sep 17 00:00:00 2001

From: Dan Streetman ddstreet@ieee.org Date: Mon, 27 Feb 2017 14:26:53 -0800 Subject: zswap: don't param_set_charp while holding spinlock

From: Dan Streetman ddstreet@ieee.org

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 dan.streetman@canonical.com Reported-by: Sergey Senozhatsky sergey.senozhatsky.work@gmail.com 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 vbabka@suse.cz 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-4.9/zswap-don-t-param_set_charp-while-holding-spinlock.patch