* [PATCH v3] ext4: prevent data-race that occur when read/write ext4_group_desc structure members
@ 2024-10-03 12:53 Jeongjun Park
2024-10-10 21:04 ` Andreas Dilger
2024-10-31 14:33 ` Theodore Ts'o
0 siblings, 2 replies; 3+ messages in thread
From: Jeongjun Park @ 2024-10-03 12:53 UTC (permalink / raw)
To: tytso, adilger.kernel
Cc: akpm, linux-ext4, linux-kernel, stable, Jeongjun Park
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@vger.kernel.org>
Fixes: ac27a0ec112a ("[PATCH] ext4: initial copy of files from ext3")
Signed-off-by: Jeongjun Park <aha310510@gmail.com>
---
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,
--
^ permalink raw reply related [flat|nested] 3+ messages in thread* Re: [PATCH v3] ext4: prevent data-race that occur when read/write ext4_group_desc structure members
2024-10-03 12:53 [PATCH v3] ext4: prevent data-race that occur when read/write ext4_group_desc structure members Jeongjun Park
@ 2024-10-10 21:04 ` Andreas Dilger
2024-10-31 14:33 ` Theodore Ts'o
1 sibling, 0 replies; 3+ messages in thread
From: Andreas Dilger @ 2024-10-10 21:04 UTC (permalink / raw)
To: Jeongjun Park; +Cc: Theodore Ts'o, akpm, Ext4 Developers List, LKML, stable
[-- Attachment #1: Type: text/plain, Size: 3771 bytes --]
On Oct 3, 2024, at 6:53 AM, Jeongjun Park <aha310510@gmail.com> wrote:
>
> 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.
Thanks for the updated patch.
Reviewed-by: Andreas Dilger <adilger@dilger.ca>
>
> [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@vger.kernel.org>
> Fixes: ac27a0ec112a ("[PATCH] ext4: initial copy of files from ext3")
> Signed-off-by: Jeongjun Park <aha310510@gmail.com>
> ---
> 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,
> --
Cheers, Andreas
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^ permalink raw reply [flat|nested] 3+ messages in thread* Re: [PATCH v3] ext4: prevent data-race that occur when read/write ext4_group_desc structure members
2024-10-03 12:53 [PATCH v3] ext4: prevent data-race that occur when read/write ext4_group_desc structure members Jeongjun Park
2024-10-10 21:04 ` Andreas Dilger
@ 2024-10-31 14:33 ` Theodore Ts'o
1 sibling, 0 replies; 3+ messages in thread
From: Theodore Ts'o @ 2024-10-31 14:33 UTC (permalink / raw)
To: adilger.kernel, Jeongjun Park
Cc: Theodore Ts'o, akpm, linux-ext4, linux-kernel, stable
On Thu, 03 Oct 2024 21:53:37 +0900, Jeongjun Park wrote:
> 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.
>
> [...]
Applied, thanks!
[1/1] ext4: prevent data-race that occur when read/write ext4_group_desc structure members
commit: 902cc179c931a033cd7f4242353aa2733bf8524c
Best regards,
--
Theodore Ts'o <tytso@mit.edu>
^ permalink raw reply [flat|nested] 3+ messages in thread
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2024-10-03 12:53 [PATCH v3] ext4: prevent data-race that occur when read/write ext4_group_desc structure members Jeongjun Park
2024-10-10 21:04 ` Andreas Dilger
2024-10-31 14:33 ` Theodore Ts'o
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