[PATCH] mm/page_alloc: Fix uninitialized variable

[76824143@qq.com]

From: Hao Zhang <zhanghao1@kylinos.cn>

The variable "compact_result" is not initialized in function
__alloc_pages_direct_compact if order is zero.

If order is zero, initialize "compact_result" to COMPACT_SKIPPED.

BUG: KMSAN: uninit-value in __alloc_pages_slowpath+0xee8/0x16c0 mm/page_alloc.c:4416
 __alloc_pages_slowpath+0xee8/0x16c0 mm/page_alloc.c:4416
 __alloc_frozen_pages_noprof+0xa4c/0xe00 mm/page_alloc.c:4752
 alloc_pages_mpol+0x4cd/0x890 mm/mempolicy.c:2270
 alloc_frozen_pages_noprof mm/mempolicy.c:2341 [inline]
 alloc_pages_noprof mm/mempolicy.c:2361 [inline]
 folio_alloc_noprof+0x1dc/0x350 mm/mempolicy.c:2371
 filemap_alloc_folio_noprof+0xa6/0x440 mm/filemap.c:1019
 __filemap_get_folio+0xb9a/0x1840 mm/filemap.c:1970
 grow_dev_folio fs/buffer.c:1039 [inline]
 grow_buffers fs/buffer.c:1105 [inline]
 __getblk_slow fs/buffer.c:1131 [inline]
 bdev_getblk+0x2c9/0xab0 fs/buffer.c:1431
 getblk_unmovable include/linux/buffer_head.h:369 [inline]
 ext4_getblk+0x3b7/0xe50 fs/ext4/inode.c:864
 ext4_bread_batch+0x9f/0x7d0 fs/ext4/inode.c:933
 __ext4_find_entry+0x1ebb/0x36c0 fs/ext4/namei.c:1627
 ext4_lookup_entry fs/ext4/namei.c:1729 [inline]
 ext4_lookup+0x189/0xb40 fs/ext4/namei.c:1797
 __lookup_slow+0x538/0x710 fs/namei.c:1793
 lookup_slow+0x6a/0xd0 fs/namei.c:1810
 walk_component fs/namei.c:2114 [inline]
 link_path_walk+0xf29/0x1420 fs/namei.c:2479
 path_openat+0x30f/0x6250 fs/namei.c:3985
 do_filp_open+0x268/0x600 fs/namei.c:4016
 do_sys_openat2+0x1bf/0x2f0 fs/open.c:1428
 do_sys_open fs/open.c:1443 [inline]
 __do_sys_openat fs/open.c:1459 [inline]
 __se_sys_openat fs/open.c:1454 [inline]
 __x64_sys_openat+0x2a1/0x310 fs/open.c:1454
 x64_sys_call+0x36f5/0x3c30 arch/x86/include/generated/asm/syscalls_64.h:258
 do_syscall_x64 arch/x86/entry/common.c:52 [inline]
 do_syscall_64+0xcd/0x1e0 arch/x86/entry/common.c:83
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

Local variable compact_result created at:
 __alloc_pages_slowpath+0x66/0x16c0 mm/page_alloc.c:4218
 __alloc_frozen_pages_noprof+0xa4c/0xe00 mm/page_alloc.c:4752

Reported-by: syzbot+0cfd5e38e96a5596f2b6@syzkaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=0cfd5e38e96a5596f2b6
Signed-off-by: Hao Zhang <zhanghao1@kylinos.cn>
---
 mm/page_alloc.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 579789600a3c..7f0136a404b5 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -3675,8 +3675,10 @@ __alloc_pages_direct_compact(gfp_t gfp_mask, unsigned int order,
 	unsigned long pflags;
 	unsigned int noreclaim_flag;
 
-	if (!order)
+	if (!order) {
+		*compact_result = COMPACT_SKIPPED;
 		return NULL;
+	}
 
 	psi_memstall_enter(&pflags);
 	delayacct_compact_start();

base-commit: d082ecbc71e9e0bf49883ee4afd435a77a5101b6
-- 
2.25.1