dm bufio: avoid false-positive Wmaybe-uninitialized warning

BugLink: http://bugs.launchpad.net/bugs/1756100
commit 590347e4000356f55eb10b03ced2686bd74dab40 upstream.

gcc-6.3 and earlier show a new warning after a seemingly unrelated
change to the arm64 PAGE_KERNEL definition:

In file included from drivers/md/dm-bufio.c:14:0:
drivers/md/dm-bufio.c: In function 'alloc_buffer':
include/linux/sched/mm.h:182:56: warning: 'noio_flag' may be used uninitialized in this function [-Wmaybe-uninitialized]
  current->flags = (current->flags & ~PF_MEMALLOC_NOIO) | flags;
                                                        ^

The same warning happened earlier on linux-3.18 for MIPS and I did a
workaround for that, but now it's come back.

gcc-7 and newer are apparently smart enough to figure this out, and
other architectures don't show it, so the best I could come up with is
to rework the caller slightly in a way that makes it obvious enough to
all arm64 compilers what is happening here.

Fixes: 41acec624087 ("arm64: kpti: Make use of nG dependent on arm64_kernel_unmapped_at_el0()")
Link: https://patchwork.kernel.org/patch/9692829/
Cc: stable@vger.kernel.org
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
[snitzer: moved declarations inside conditional, altered vmalloc return]
Signed-off-by: Mike Snitzer <snitzer@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Thadeu Lima de Souza Cascardo <cascardo@canonical.com>

diff --git a/drivers/md/dm-bufio.c b/drivers/md/dm-bufio.c
index c546b567f3b50a3f43b0c074e9319ca908ec5971..b3454e8c09561dd41d6a0a905027aa8350cbb874 100644 (file)
--- a/drivers/md/dm-bufio.c
+++ b/drivers/md/dm-bufio.c
@@ -386,9 +386,6 @@ static void __cache_size_refresh(void)
 static void *alloc_buffer_data(struct dm_bufio_client *c, gfp_t gfp_mask,
                               enum data_mode *data_mode)
 {
-       unsigned noio_flag;
-       void *ptr;
-
        if (c->block_size <= DM_BUFIO_BLOCK_SIZE_SLAB_LIMIT) {
                *data_mode = DATA_MODE_SLAB;
                return kmem_cache_alloc(DM_BUFIO_CACHE(c), gfp_mask);
@@ -412,16 +409,15 @@ static void *alloc_buffer_data(struct dm_bufio_client *c, gfp_t gfp_mask,
         * all allocations done by this process (including pagetables) are done
         * as if GFP_NOIO was specified.
         */
+       if (gfp_mask & __GFP_NORETRY) {
+               unsigned noio_flag = memalloc_noio_save();
+               void *ptr = __vmalloc(c->block_size, gfp_mask, PAGE_KERNEL);
 
-       if (gfp_mask & __GFP_NORETRY)
-               noio_flag = memalloc_noio_save();
-
-       ptr = __vmalloc(c->block_size, gfp_mask, PAGE_KERNEL);
-
-       if (gfp_mask & __GFP_NORETRY)
                memalloc_noio_restore(noio_flag);
+               return ptr;
+       }
 
-       return ptr;
+       return __vmalloc(c->block_size, gfp_mask, PAGE_KERNEL);
 }
 
 /*