linux-kernel - [PATCH] btrfs: zoned: fix uninitialized max_chunk

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Date:   Tue, 23 Mar 2021 13:46:19 +0100
From:   Arnd Bergmann <arnd@...nel.org>
To:     Chris Mason <clm@...com>, Josef Bacik <josef@...icpanda.com>,
        David Sterba <dsterba@...e.com>,
        Anand Jain <anand.jain@...cle.com>,
        Naohiro Aota <naohiro.aota@....com>
Cc:     Arnd Bergmann <arnd@...db.de>, Nikolay Borisov <nborisov@...e.com>,
        Johannes Thumshirn <johannes.thumshirn@....com>,
        linux-btrfs@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: [PATCH] btrfs: zoned: fix uninitialized max_chunk_size

From: Arnd Bergmann <arnd@...db.de>

The ctl->max_chunk_size member might be used uninitialized
when none of the three conditions for initializing it in
init_alloc_chunk_ctl_policy_zoned() are true:

In function ‘init_alloc_chunk_ctl_policy_zoned’,
    inlined from ‘init_alloc_chunk_ctl’ at fs/btrfs/volumes.c:5023:3,
    inlined from ‘btrfs_alloc_chunk’ at fs/btrfs/volumes.c:5340:2:
include/linux/compiler-gcc.h:48:45: error: ‘ctl.max_chunk_size’ may be used uninitialized [-Werror=maybe-uninitialized]
 4998 |         ctl->max_chunk_size = min(limit, ctl->max_chunk_size);
      |                               ^~~
fs/btrfs/volumes.c: In function ‘btrfs_alloc_chunk’:
fs/btrfs/volumes.c:5316:32: note: ‘ctl’ declared here
 5316 |         struct alloc_chunk_ctl ctl;
      |                                ^~~

Initialize it to UINT_MAX and rely on the min() expression to limit
it.

Fixes: 1cd6121f2a38 ("btrfs: zoned: implement zoned chunk allocator")
Signed-off-by: Arnd Bergmann <arnd@...db.de>
---
Note that the -Wmaybe-unintialized warning is globally disabled
by default. For some reason I got this warning anyway when building
this specific file with gcc-11.
---
 fs/btrfs/volumes.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/fs/btrfs/volumes.c b/fs/btrfs/volumes.c
index bc3b33efddc5..b42b423b6a10 100644
--- a/fs/btrfs/volumes.c
+++ b/fs/btrfs/volumes.c
@@ -4980,6 +4980,7 @@ static void init_alloc_chunk_ctl_policy_zoned(
 	u64 type = ctl->type;
 
 	ctl->max_stripe_size = zone_size;
+	ctl->max_chunk_size = UINT_MAX;
 	if (type & BTRFS_BLOCK_GROUP_DATA) {
 		ctl->max_chunk_size = round_down(BTRFS_MAX_DATA_CHUNK_SIZE,
 						 zone_size);
-- 
2.29.2