| From | Greg Kroah-Hartman <> | Subject | [PATCH 4.9 25/96] zswap: dont param_set_charp while holding spinlock | Date | Mon, 15 Jan 2018 13:34:24 +0100 |
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4.9-stable review patch. If anyone has any objections, please let me know.
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From: Dan Streetman <ddstreet@ieee.org>
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> --- mm/zswap.c | 12 ++++++++---- 1 file changed, 8 insertions(+), 4 deletions(-)
--- a/mm/zswap.c +++ b/mm/zswap.c @@ -752,18 +752,22 @@ 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);
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