linux-kernel - [PATCH] dm-bufio: avoid false-positive Wmaybe-uninitialized warning

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Date:   Thu, 22 Feb 2018 16:56:16 +0100
From:   Arnd Bergmann <arnd@...db.de>
To:     Alasdair Kergon <agk@...hat.com>,
        Mike Snitzer <snitzer@...hat.com>, dm-devel@...hat.com
Cc:     Arnd Bergmann <arnd@...db.de>,
        Mikulas Patocka <mpatocka@...hat.com>,
        Ingo Molnar <mingo@...nel.org>,
        Aliaksei Karaliou <akaraliou.dev@...il.com>,
        Jens Axboe <axboe@...nel.dk>, Jan Kara <jack@...e.cz>,
        Dan Carpenter <dan.carpenter@...cle.com>,
        Mark Rutland <mark.rutland@....com>,
        Eric Biggers <ebiggers@...gle.com>,
        linux-kernel@...r.kernel.org
Subject: [PATCH] dm-bufio: avoid false-positive Wmaybe-uninitialized warning

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/
Signed-off-by: Arnd Bergmann <arnd@...db.de>
---
 drivers/md/dm-bufio.c | 10 +++++-----
 1 file changed, 5 insertions(+), 5 deletions(-)

diff --git a/drivers/md/dm-bufio.c b/drivers/md/dm-bufio.c
index 414c9af54ded..e7ad6fc6a5ea 100644
--- a/drivers/md/dm-bufio.c
+++ b/drivers/md/dm-bufio.c
@@ -413,13 +413,13 @@ static void *alloc_buffer_data(struct dm_bufio_client *c, gfp_t gfp_mask,
 	 * as if GFP_NOIO was specified.
 	 */
 
-	if (gfp_mask & __GFP_NORETRY)
+	if (gfp_mask & __GFP_NORETRY) {
 		noio_flag = memalloc_noio_save();
-
-	ptr = __vmalloc(c->block_size, gfp_mask, PAGE_KERNEL);
-
-	if (gfp_mask & __GFP_NORETRY)
+		ptr = __vmalloc(c->block_size, gfp_mask, PAGE_KERNEL);
 		memalloc_noio_restore(noio_flag);
+	} else {
+		ptr = __vmalloc(c->block_size, gfp_mask, PAGE_KERNEL);
+	}
 
 	return ptr;
 }
-- 
2.9.0