Commit fd5bb66c authored by Dan Streetman's avatar Dan Streetman Committed by Linus Torvalds
Browse files

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: c99b42c3 ("zswap: use charp for zswap param strings")

Signed-off-by: default avatarDan Streetman <>
Reported-by: default avatarSergey Senozhatsky <>
Cc: Michal Hocko <>
Cc: Minchan Kim <>
Signed-off-by: default avatarAndrew Morton <>
Signed-off-by: default avatarLinus Torvalds <>
parent bae21db8
......@@ -704,18 +704,22 @@ static int __zswap_param_set(const char *val, const struct kernel_param *kp,
pool = zswap_pool_find_get(type, compressor);
if (pool) {
zswap_pool_debug("using existing", pool);
WARN_ON(pool == zswap_pool_current());
} else {
pool = zswap_pool_create(type, compressor);
if (!pool)
pool = zswap_pool_create(type, compressor);
if (pool)
ret = param_set_charp(s, kp);
ret = -EINVAL;
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 *val, const struct kernel_param *kp,
list_add_tail_rcu(&pool->list, &zswap_pools);
put_pool = pool;
} else if (!zswap_has_pool) {
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 *val, const struct kernel_param *kp,
ret = param_set_charp(s, kp);
/* drop the ref from either the old current pool,
* or the new pool we failed to add
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