Re: [PATCH] ext4: goto right label 'out_mmap_sem' in ext4_setattr()

[Brian Foster <bfoster@redhat.com>]

On Thu, Feb 13, 2025 at 07:22:47PM +0800, libaokun@huaweicloud.com wrote:
> From: Baokun Li <libaokun1@huawei.com>
> 
> Otherwise, if ext4_inode_attach_jinode() fails, a hung task will
> happen because filemap_invalidate_unlock() isn't called to unlock
> mapping->invalidate_lock. Like this:
> 
> EXT4-fs error (device sda) in ext4_setattr:5557: Out of memory
> INFO: task fsstress:374 blocked for more than 122 seconds.
>       Not tainted 6.14.0-rc1-next-20250206-xfstests-dirty #726
> "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
> task:fsstress state:D stack:0     pid:374   tgid:374   ppid:373
>                                   task_flags:0x440140 flags:0x00000000
> Call Trace:
>  <TASK>
>  __schedule+0x2c9/0x7f0
>  schedule+0x27/0xa0
>  schedule_preempt_disabled+0x15/0x30
>  rwsem_down_read_slowpath+0x278/0x4c0
>  down_read+0x59/0xb0
>  page_cache_ra_unbounded+0x65/0x1b0
>  filemap_get_pages+0x124/0x3e0
>  filemap_read+0x114/0x3d0
>  vfs_read+0x297/0x360
>  ksys_read+0x6c/0xe0
>  do_syscall_64+0x4b/0x110
>  entry_SYSCALL_64_after_hwframe+0x76/0x7e
> 
> Fixes: c7fc0366c656 ("ext4: partial zero eof block on unaligned inode size extension")
> Signed-off-by: Baokun Li <libaokun1@huawei.com>
> ---

First off, thank you for catching this. :)

>  fs/ext4/inode.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
> index 3cc8da6357aa..04ffd802dbde 100644
> --- a/fs/ext4/inode.c
> +++ b/fs/ext4/inode.c
> @@ -5452,7 +5452,7 @@ int ext4_setattr(struct mnt_idmap *idmap, struct dentry *dentry,
>  			    oldsize & (inode->i_sb->s_blocksize - 1)) {
>  				error = ext4_inode_attach_jinode(inode);
>  				if (error)
> -					goto err_out;
> +					goto out_mmap_sem;
>  			}

This looks reasonable to me, but I notice that the immediate previous
error check looks like this:

		...
                rc = ext4_break_layouts(inode);
                if (rc) {
                        filemap_invalidate_unlock(inode->i_mapping);
                        goto err_out;
                }
		...

... and then the following after the broken logic uses out_mmap_sem.
Could we be a little more consistent here one way or the other? The
change looks functionally correct to me either way:

Reviewed-by: Brian Foster <bfoster@redhat.com>

Brian

>  
>  			handle = ext4_journal_start(inode, EXT4_HT_INODE, 3);
> -- 
> 2.39.2
> 
>