Re: [PATCH -next] ext4: fix bug_on in ext4_writepages

yebin
2022-05-06T12:48:54Z

On 2022/5/6 16:50, Jan Kara wrote:
> On Fri 06-05-22 09:27:25, yebin wrote:
>> On 2022/5/5 23:47, Jan Kara wrote:
>>> On Thu 05-05-22 21:57:08, Ye Bin wrote:
>>>> we got issue as follows:
>>>> EXT4-fs error (device loop0): ext4_mb_generate_buddy:1141: group 0, block bitmap and bg descriptor inconsistent: 25 vs 31513 free cls
>>>> ------------[ cut here ]------------
>>>> kernel BUG at fs/ext4/inode.c:2708!
>>>> invalid opcode: 0000 [#1] PREEMPT SMP KASAN PTI
>>>> CPU: 2 PID: 2147 Comm: rep Not tainted 5.18.0-rc2-next-20220413+ #155
>>>> RIP: 0010:ext4_writepages+0x1977/0x1c10
>>>> RSP: 0018:ffff88811d3e7880 EFLAGS: 00010246
>>>> RAX: 0000000000000000 RBX: 0000000000000001 RCX: ffff88811c098000
>>>> RDX: 0000000000000000 RSI: ffff88811c098000 RDI: 0000000000000002
>>>> RBP: ffff888128140f50 R08: ffffffffb1ff6387 R09: 0000000000000000
>>>> R10: 0000000000000007 R11: ffffed10250281ea R12: 0000000000000001
>>>> R13: 00000000000000a4 R14: ffff88811d3e7bb8 R15: ffff888128141028
>>>> FS: 00007f443aed9740(0000) GS:ffff8883aef00000(0000) knlGS:0000000000000000
>>>> CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
>>>> CR2: 0000000020007200 CR3: 000000011c2a4000 CR4: 00000000000006e0
>>>> DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
>>>> DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
>>>> Call Trace:
>>>> <TASK>
>>>> do_writepages+0x130/0x3a0
>>>> filemap_fdatawrite_wbc+0x83/0xa0
>>>> filemap_flush+0xab/0xe0
>>>> ext4_alloc_da_blocks+0x51/0x120
>>>> __ext4_ioctl+0x1534/0x3210
>>>> __x64_sys_ioctl+0x12c/0x170
>>>> do_syscall_64+0x3b/0x90
>>>>
>>>> It may happen as follows:
>>>> 1. write inline_data inode
>>>> vfs_write
>>>> new_sync_write
>>>> ext4_file_write_iter
>>>> ext4_buffered_write_iter
>>>> generic_perform_write
>>>> ext4_da_write_begin
>>>> ext4_da_write_inline_data_begin -> If inline data size too
>>>> small will allocate block to write, then mapping will has
>>>> dirty page
>>>> ext4_da_convert_inline_data_to_extent ->clear EXT4_STATE_MAY_INLINE_DATA
>>>> 2. fallocate
>>>> do_vfs_ioctl
>>>> ioctl_preallocate
>>>> vfs_fallocate
>>>> ext4_fallocate
>>>> ext4_convert_inline_data
>>>> ext4_convert_inline_data_nolock
>>>> ext4_map_blocks -> fail will goto restore data
>>>> ext4_restore_inline_data
>>>> ext4_create_inline_data
>>>> ext4_write_inline_data
>>>> ext4_set_inode_state -> set inode EXT4_STATE_MAY_INLINE_DATA
>>>> 3. writepages
>>>> __ext4_ioctl
>>>> ext4_alloc_da_blocks
>>>> filemap_flush
>>>> filemap_fdatawrite_wbc
>>>> do_writepages
>>>> ext4_writepages
>>>> if (ext4_has_inline_data(inode))
>>>> BUG_ON(ext4_test_inode_state(inode, EXT4_STATE_MAY_INLINE_DATA))
>>>>
>>>> To solved this issue, record origin 'EXT4_STATE_MAY_INLINE_DATA' flag, then pass
>>>> value to 'ext4_restore_inline_data', 'ext4_restore_inline_data' will
>>>> decide to if recovery 'EXT4_STATE_MAY_INLINE_DATA' flag according to parameter.
>>>>
>>>> Signed-off-by: Ye Bin <yebin10@huawei.com>
>>> I think this will get also fixed by a patch from your colleague I've
>>> reviewed here [1], won't it?
>>>
>>> [1] https://lore.kernel.org/all/20220428165725.mvjh6mx7gr5vekqe@quack3.lan
>>>
>> The issue I fixed is not the same as the isuue my colleague fixed.
> OK, maybe I've jumped to conclusion too early but the fix I've referenced
> above will protect ext4_convert_inline_data() in ext4_fallocate() with
> inode->i_rwsem so I think the race you describe with ext4_da_write_begin()
> cannot happen. The inline conversion path with be entered either from
> ext4_da_write_begin() or from ext4_fallocate() but not from both. If I'm
> missing something, please explain how you think the problem happens with
> the above fix applied... Thanks!
>
> Honza
It's happen as follows:
step1:
ext4_file_write_iter
ext4_buffered_write_iter
generic_perform_write
ext4_da_write_begin
if (ext4_test_inode_state(inode, EXT4_STATE_MAY_INLINE_DATA))
ext4_da_write_inline_data_begin
ext4_da_convert_inline_data_to_extent
__block_write_begin
ext4_clear_inode_state(inode, EXT4_STATE_MAY_INLINE_DATA);
->clear EXT4_STATE_MAY_INLINE_DATA flag, If inline data
size too
small will allocate block to write, then mapping will has dirty
page

ext4_da_write_end
generic_write_end

step2：
vfs_fallocate
ext4_fallocate
ext4_convert_inline_data
if (ext4_has_inline_data(inode)) -> This condition is satisfied
ext4_convert_inline_data_nolock
ext4_map_blocks -> fail will goto restore data
ext4_restore_inline_data
ext4_create_inline_data
ext4_write_inline_data
ext4_set_inode_state -> set inode EXT4_STATE_MAY_INLINE_DATA
step3:
do_writepages
ext4_writepages
if (ext4_has_inline_data(inode))
BUG_ON(ext4_test_inode_state(inode, EXT4_STATE_MAY_INLINE_DATA))

As we call "ext4_destroy_inline_data" to destory inline data when delay
allocation.
So，if we call fallocate before writepages while ext4_map_blocks return
failed,
will lead to above issue.
This issue does not require concurrency conditions.

>>>> ---
>>>> fs/ext4/inline.c | 13 +++++++++----
>>>> 1 file changed, 9 insertions(+), 4 deletions(-)
>>>>
>>>> diff --git a/fs/ext4/inline.c b/fs/ext4/inline.c
>>>> index 9c076262770d..407061c79adc 100644
>>>> --- a/fs/ext4/inline.c
>>>> +++ b/fs/ext4/inline.c
>>>> @@ -1125,8 +1125,8 @@ static int ext4_update_inline_dir(handle_t *handle, struct inode *dir,
>>>> }
>>>> static void ext4_restore_inline_data(handle_t *handle, struct inode *inode,
>>>> - struct ext4_iloc *iloc,
>>>> - void *buf, int inline_size)
>>>> + struct ext4_iloc *iloc, void *buf,
>>>> + int inline_size, bool has_data)
>>>> {
>>>> int ret;
>>>> @@ -1138,7 +1138,8 @@ static void ext4_restore_inline_data(handle_t *handle, struct inode *inode,
>>>> return;
>>>> }
>>>> ext4_write_inline_data(inode, iloc, buf, 0, inline_size);
>>>> - ext4_set_inode_state(inode, EXT4_STATE_MAY_INLINE_DATA);
>>>> + if (has_data)
>>>> + ext4_set_inode_state(inode, EXT4_STATE_MAY_INLINE_DATA);
>>>> }
>>>> static int ext4_finish_convert_inline_dir(handle_t *handle,
>>>> @@ -1194,6 +1195,7 @@ static int ext4_convert_inline_data_nolock(handle_t *handle,
>>>> struct buffer_head *data_bh = NULL;
>>>> struct ext4_map_blocks map;
>>>> int inline_size;
>>>> + bool has_data;
>>>> inline_size = ext4_get_inline_size(inode);
>>>> buf = kmalloc(inline_size, GFP_NOFS);
>>>> @@ -1222,6 +1224,8 @@ static int ext4_convert_inline_data_nolock(handle_t *handle,
>>>> if (error)
>>>> goto out;
>>>> + has_data = !!ext4_test_inode_state(inode, EXT4_STATE_MAY_INLINE_DATA);
>>>> +
>>>> map.m_lblk = 0;
>>>> map.m_len = 1;
>>>> map.m_flags = 0;
>>>> @@ -1262,7 +1266,8 @@ static int ext4_convert_inline_data_nolock(handle_t *handle,
>>>> unlock_buffer(data_bh);
>>>> out_restore:
>>>> if (error)
>>>> - ext4_restore_inline_data(handle, inode, iloc, buf, inline_size);
>>>> + ext4_restore_inline_data(handle, inode, iloc, buf,
>>>> + inline_size, has_data);
>>>> out:
>>>> brelse(data_bh);
>>>> --
>>>> 2.31.1
>>>>