block: avoid using uninitialized value in from queue_var_store

As found by gcc-4.8, the QUEUE_SYSFS_BIT_FNS macro creates functions
that use a value generated by queue_var_store independent of whether
that value was set or not.

block/blk-sysfs.c: In function 'queue_store_nonrot':
block/blk-sysfs.c:244:385: warning: 'val' may be used uninitialized in this function [-Wmaybe-uninitialized]

Unlike most other such warnings, this one is not a false positive,
writing any non-number string into the sysfs files indeed has
an undefined result, rather than returning an error.

Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

1 files changed, 2 insertions, 0 deletions

diff --git a/block/blk-sysfs.c b/block/blk-sysfs.c
index 6206a934eb8c..5efc5a647183 100644
--- a/block/blk-sysfs.c
+++ b/block/blk-sysfs.c
@@ -229,6 +229,8 @@ queue_store_##name(struct request_queue *q, const char *page, size_t count) \
         unsigned long val;                                              \
         ssize_t ret;                                                    \
         ret = queue_var_store(&val, page, count);                       \
+        if (ret < 0)                                                    \
+                 return ret;                                            \
         if (neg)                                                        \
                 val = !val;                                             \
                                                                         \