Patch "dm bufio: avoid false-positive Wmaybe-uninitialized warning" has been added to the 4.14-stable tree

This is a note to let you know that I've just added the patch titled

dm bufio: avoid false-positive Wmaybe-uninitialized warning

to the 4.14-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
dm-bufio-avoid-false-positive-wmaybe-uninitialized-warning.patch
and it can be found in the queue-4.14 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: Arnd Bergmann <[email protected]>
Date: Thu, 22 Feb 2018 16:56:16 +0100
Subject: dm bufio: avoid false-positive Wmaybe-uninitialized warning

From: Arnd Bergmann <[email protected]>

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.

---
 drivers/md/dm-bufio.c |   16 ++++++----------
 1 file changed, 6 insertions(+), 10 deletions(-)

@@ -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
 	 * 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);
 }
 
 /*

Patches currently in stable-queue which might be from [email protected] are

queue-4.14/dm-bufio-avoid-false-positive-wmaybe-uninitialized-warning.patch