Currently, data-race like [1] occur in fs/ext4/ialloc.c
find_group_other() and find_group_orlov() read *_lo, *_hi with
ext4_free_inodes_count without additional locking. This can cause data-race,
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.
[1]
==================================================================
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
value changed: 0x185c -> 0x185b
Cc: <stable@xxxxxxxxxxxxxxx>
Fixes: ac27a0ec112a ("[PATCH] ext4: initial copy of files from ext3")
Signed-off-by: Jeongjun Park <aha310510@xxxxxxxxx>
---
fs/ext4/super.c | 8 ++++----
1 file changed, 4 insertions(+), 4 deletions(-)
diff --git a/fs/ext4/super.c b/fs/ext4/super.c
index 16a4ce704460..8337c4999f90 100644
--- a/fs/ext4/super.c
+++ b/fs/ext4/super.c
@@ -346,9 +346,9 @@ __u32 ext4_free_group_clusters(struct super_block *sb,
__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,
@@ -402,9 +402,9 @@ void ext4_free_group_clusters_set(struct super_block *sb,
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,
--
