block: bfq: swap puts in bfqg_and_blkg_put

BugLink: https://bugs.launchpad.net/bugs/1836117
commit d5274b3cd6a814ccb2f56d81ee87cbbf51bd4cf7 upstream.

Fix trivial use-after-free. This could be last reference to bfqg.

Fixes: 8f9bebc33dd7 ("block, bfq: access and cache blkg data only when safe")
Acked-by: Paolo Valente <paolo.valente@linaro.org>
Signed-off-by: Konstantin Khlebnikov <khlebnikov@yandex-team.ru>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Kamal Mostafa <kamal@canonical.com>
Signed-off-by: Kleber Sacilotto de Souza <kleber.souza@canonical.com>

diff --git a/block/bfq-cgroup.c b/block/bfq-cgroup.c
index c5d8142368c70e0aaa6fbda915777b2b6d90882b..f0d554af14c7226e7325fe0dea2e2ed819b82349 100644 (file)
--- a/block/bfq-cgroup.c
+++ b/block/bfq-cgroup.c
@@ -275,9 +275,9 @@ static void bfqg_and_blkg_get(struct bfq_group *bfqg)
 
 void bfqg_and_blkg_put(struct bfq_group *bfqg)
 {
-       bfqg_put(bfqg);
-
        blkg_put(bfqg_to_blkg(bfqg));
+
+       bfqg_put(bfqg);
 }
 
 /* @stats = 0 */