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zswap: don't param_set_charp while holding spinlock

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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: c99b42c352 ("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>
This commit is contained in:
Dan Streetman 2017-02-27 14:26:53 -08:00 committed by Linus Torvalds
parent bae21db88b
commit fd5bb66cd9
1 changed files with 13 additions and 7 deletions
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20
mm/zswap.c
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@ -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());
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 *val, const struct kernel_param *kp,
*/
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 *val, const struct kernel_param *kp,
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
*/