From: Dan Streetman <ddstreet@xxxxxxxx>
Subject: zswap: don't param_set_charp while holding spinlock
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@xxxxxxxx
Signed-off-by: Dan Streetman <dan.streetman@xxxxxxxxxxxxx>
Reported-by: Sergey Senozhatsky <sergey.senozhatsky.work@xxxxxxxxx>
Cc: Michal Hocko <mhocko@xxxxxxxxxx>
Cc: Minchan Kim <minchan@xxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
mm/zswap.c | 20 +++++++++++++-------
1 file changed, 13 insertions(+), 7 deletions(-)
diff -puN mm/zswap.c~zswap-dont-param_set_charp-while-holding-spinlock mm/zswap.c
--- a/mm/zswap.c~zswap-dont-param_set_charp-while-holding-spinlock
+++ a/mm/zswap.c
@@ -704,18 +704,22 @@ 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);
@@ -727,7 +731,11 @@ static int __zswap_param_set(const char
*/
list_add_tail_rcu(&pool->list, &zswap_pools);
put_pool = pool;
- } else if (!zswap_has_pool) {
+ }
+
+ spin_unlock(&zswap_pools_lock);
+
+ if (!zswap_has_pool && !pool) {
/* if initial pool creation failed, and this pool creation also
* failed, maybe both compressor and zpool params were bad.
* Allow changing this param, so pool creation will succeed
@@ -738,8 +746,6 @@ static int __zswap_param_set(const char
ret = param_set_charp(s, kp);
}
- spin_unlock(&zswap_pools_lock);
-
/* drop the ref from either the old current pool,
* or the new pool we failed to add
*/
_
--
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