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

[Jan Kara <jack@suse.cz>]

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

> > > ---
> > >   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
> > > 
> 
-- 
Jan Kara <jack@suse.com>
SUSE Labs, CR