Re: [PATCH -next v2] ext4: fix bug_on in ext4_writepages

[yebin <yebin10@huawei.com>]

On 2022/5/11 21:47, Jan Kara wrote:
> On Tue 10-05-22 18:02:28, 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))
>>
>> The root cause of this issue is we destory inline data until call ext4_writepages
>> under delay allocation mode. But there maybe already covert from inline to extent.
>> To solved this issue, we call filemap_flush firstly.
>>
>> Signed-off-by: Ye Bin <yebin10@huawei.com>
>> ---
>>   fs/ext4/inline.c | 8 ++++++++
>>   1 file changed, 8 insertions(+)
>>
>> diff --git a/fs/ext4/inline.c b/fs/ext4/inline.c
>> index 6d253edebf9f..130ed5d83734 100644
>> --- a/fs/ext4/inline.c
>> +++ b/fs/ext4/inline.c
>> @@ -2002,6 +2002,14 @@ int ext4_convert_inline_data(struct inode *inode)
>>   	if (!ext4_has_inline_data(inode)) {
>>   		ext4_clear_inode_state(inode, EXT4_STATE_MAY_INLINE_DATA);
>>   		return 0;
>> +	} else if (test_opt(inode->i_sb, DELALLOC) && !S_ISDIR(inode->i_mode)) {
>> +		error = filemap_flush(inode->i_mapping);
> This is actually an interesting option and I kind of like it but shouldn't
> we restrict this to the situation when EXT4_STATE_MAY_INLINE_DATA is clear?
> Otherwise we would be writing out inline data to the inode unnecessarily
> for each ext4_convert_inline_data() call.
>
> 								Honza
Acctually,  this issue only exist in delay allocate mode. Do we need to 
restrict this to
“test_opt(inode->i_sb, DELALLOC)” as follows ?
@@ -2002,6 +2002,13 @@ int ext4_convert_inline_data(struct inode *inode)
         if (!ext4_has_inline_data(inode)) {
                 ext4_clear_inode_state(inode, EXT4_STATE_MAY_INLINE_DATA);
                 return 0;
+       } else if (test_opt(inode->i_sb, DELALLOC) &&
+                  !ext4_test_inode_state(inode, 
EXT4_STATE_MAY_INLINE_DATA)) {
+               error = filemap_flush(inode->i_mapping);
+               if (error)
+                       return error;
+               if (!ext4_has_inline_data(inode))
+                       return 0;
         }