[PATCH 4.19 100/138] ext4: supress data-race warnings in ext4_free_inodes_{count,set}()

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4.19-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Jeongjun Park <aha310510@xxxxxxxxx>

commit 902cc179c931a033cd7f4242353aa2733bf8524c upstream.

find_group_other() and find_group_orlov() read *_lo, *_hi with
ext4_free_inodes_count without additional locking. This can cause
data-race warning, but since the lock is held for most writes and free
inodes value is generally not a problem even if it is incorrect, it is
more appropriate to use READ_ONCE()/WRITE_ONCE() than to add locking.

==================================================================
BUG: KCSAN: data-race in ext4_free_inodes_count / ext4_free_inodes_set

write to 0xffff88810404300e of 2 bytes by task 6254 on cpu 1:
 ext4_free_inodes_set+0x1f/0x80 fs/ext4/super.c:405
 __ext4_new_inode+0x15ca/0x2200 fs/ext4/ialloc.c:1216
 ext4_symlink+0x242/0x5a0 fs/ext4/namei.c:3391
 vfs_symlink+0xca/0x1d0 fs/namei.c:4615
 do_symlinkat+0xe3/0x340 fs/namei.c:4641
 __do_sys_symlinkat fs/namei.c:4657 [inline]
 __se_sys_symlinkat fs/namei.c:4654 [inline]
 __x64_sys_symlinkat+0x5e/0x70 fs/namei.c:4654
 x64_sys_call+0x1dda/0x2d60 arch/x86/include/generated/asm/syscalls_64.h:267
 do_syscall_x64 arch/x86/entry/common.c:52 [inline]
 do_syscall_64+0x54/0x120 arch/x86/entry/common.c:83
 entry_SYSCALL_64_after_hwframe+0x76/0x7e

read to 0xffff88810404300e of 2 bytes by task 6257 on cpu 0:
 ext4_free_inodes_count+0x1c/0x80 fs/ext4/super.c:349
 find_group_other fs/ext4/ialloc.c:594 [inline]
 __ext4_new_inode+0x6ec/0x2200 fs/ext4/ialloc.c:1017
 ext4_symlink+0x242/0x5a0 fs/ext4/namei.c:3391
 vfs_symlink+0xca/0x1d0 fs/namei.c:4615
 do_symlinkat+0xe3/0x340 fs/namei.c:4641
 __do_sys_symlinkat fs/namei.c:4657 [inline]
 __se_sys_symlinkat fs/namei.c:4654 [inline]
 __x64_sys_symlinkat+0x5e/0x70 fs/namei.c:4654
 x64_sys_call+0x1dda/0x2d60 arch/x86/include/generated/asm/syscalls_64.h:267
 do_syscall_x64 arch/x86/entry/common.c:52 [inline]
 do_syscall_64+0x54/0x120 arch/x86/entry/common.c:83
 entry_SYSCALL_64_after_hwframe+0x76/0x7e

Cc: stable@xxxxxxxxxxxxxxx
Signed-off-by: Jeongjun Park <aha310510@xxxxxxxxx>
Reviewed-by: Andreas Dilger <adilger@xxxxxxxxx>
Link: https://patch.msgid.link/20241003125337.47283-1-aha310510@xxxxxxxxx
Signed-off-by: Theodore Ts'o <tytso@xxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
 fs/ext4/super.c |    8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

--- a/fs/ext4/super.c
+++ b/fs/ext4/super.c
@@ -258,9 +258,9 @@ __u32 ext4_free_group_clusters(struct su
 __u32 ext4_free_inodes_count(struct super_block *sb,
 			      struct ext4_group_desc *bg)
 {
-	return le16_to_cpu(bg->bg_free_inodes_count_lo) |
+	return le16_to_cpu(READ_ONCE(bg->bg_free_inodes_count_lo)) |
 		(EXT4_DESC_SIZE(sb) >= EXT4_MIN_DESC_SIZE_64BIT ?
-		 (__u32)le16_to_cpu(bg->bg_free_inodes_count_hi) << 16 : 0);
+		 (__u32)le16_to_cpu(READ_ONCE(bg->bg_free_inodes_count_hi)) << 16 : 0);
 }
 
 __u32 ext4_used_dirs_count(struct super_block *sb,
@@ -314,9 +314,9 @@ void ext4_free_group_clusters_set(struct
 void ext4_free_inodes_set(struct super_block *sb,
 			  struct ext4_group_desc *bg, __u32 count)
 {
-	bg->bg_free_inodes_count_lo = cpu_to_le16((__u16)count);
+	WRITE_ONCE(bg->bg_free_inodes_count_lo, cpu_to_le16((__u16)count));
 	if (EXT4_DESC_SIZE(sb) >= EXT4_MIN_DESC_SIZE_64BIT)
-		bg->bg_free_inodes_count_hi = cpu_to_le16(count >> 16);
+		WRITE_ONCE(bg->bg_free_inodes_count_hi, cpu_to_le16(count >> 16));
 }
 
 void ext4_used_dirs_set(struct super_block *sb,






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