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Commit fd5bb66c authored by Dan Streetman's avatar Dan Streetman Committed by Linus Torvalds
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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")
Link: http://lkml.kernel.org/r/20170126155821.4545-1-ddstreet@ieee.org


Signed-off-by: default avatarDan Streetman <dan.streetman@canonical.com>
Reported-by: default avatarSergey Senozhatsky <sergey.senozhatsky.work@gmail.com>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: Minchan Kim <minchan@kernel.org>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent bae21db8

mm/zswap.c

+13 −7
Original line number Diff line number Diff line
@@ -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);



	if (!pool)

		pool = zswap_pool_create(type, compressor);

		spin_lock(&zswap_pools_lock);

	}



	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

	 */