zswap: don't param_set_charp while holding spinlock
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>
diff --git a/mm/zswap.c b/mm/zswap.c
index dbef278..ded051e 100644
--- a/mm/zswap.c
+++ b/mm/zswap.c
@@ -752,18 +752,22 @@
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);