linux-kernel - [PATCH 4.4 29/87] zswap: dont param_set

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Message-Id: <20180115123352.235573866@linuxfoundation.org>
Date:   Mon, 15 Jan 2018 13:34:28 +0100
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org,
        Dan Streetman <dan.streetman@...onical.com>,
        Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>,
        Michal Hocko <mhocko@...nel.org>,
        Minchan Kim <minchan@...nel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Vlastimil Babka <vbabka@...e.cz>
Subject: [PATCH 4.4 29/87] zswap: dont param_set_charp while holding spinlock

4.4-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Dan Streetman <ddstreet@...e.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@...onical.com>
Reported-by: Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>
Cc: Michal Hocko <mhocko@...nel.org>
Cc: Minchan Kim <minchan@...nel.org>
Signed-off-by: Andrew Morton <akpm@...ux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@...ux-foundation.org>
Signed-off-by: Vlastimil Babka <vbabka@...e.cz>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.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);