[Bug 216343] New: XFS: no space left in xlog cause system hang

[bugzilla-daemon@kernel.org]

https://bugzilla.kernel.org/show_bug.cgi?id=216343

            Bug ID: 216343
           Summary: XFS: no space left in xlog cause system hang
           Product: File System
           Version: 2.5
    Kernel Version: 5.10.38
          Hardware: ARM
                OS: Linux
              Tree: Mainline
            Status: NEW
          Severity: normal
          Priority: P1
         Component: XFS
          Assignee: filesystem_xfs@kernel-bugs.kernel.org
          Reporter: zhoukete@126.com
        Regression: No

Created attachment 301539
  --> https://bugzilla.kernel.org/attachment.cgi?id=301539&action=edit
stack

1. cannot login with ssh, system hanged and cannot do anything
2. dmesg report 'audit: audit_backlog=41349 > audit_backlog_limit=8192'
3. I send sysrq-crash and get vmcore file , I dont know how to reproduce it.

Follwing is my analysis from vmcore:

The reason why tty cannot login is pid 2021571 hold the acct_process mutex, and
2021571 cannot release mutex because it is wait for xlog release space. See the
stac info in the attachment of stack.txt

So I try to figure out what happened to xlog

crash> struct xfs_ail.ail_target_prev,ail_targe,ail_head 0xffff00ff884f1000 
  ail_target_prev = 0xe9200058600
  ail_target = 0xe9200058600
  ail_head = {
    next = 0xffff0340999a0a80, 
    prev = 0xffff020013c66b40
  }

there are 112 log item in ail list
crash> list 0xffff0340999a0a80 | wc -l
112 

79 item of them are xlog_inode_item
30 item of them are xlog_buf_item

crash> xfs_log_item.li_flags,li_lsn 0xffff0340999a0a80 -x 
  li_flags = 0x1
  li_lsn = 0xe910005cc00 ===> first item lsn

crash> xfs_log_item.li_flags,li_lsn ffff020013c66b40 -x
  li_flags = 0x1
  li_lsn = 0xe9200058600 ===> last item lsn

crash>xfs_log_item.li_buf 0xffff0340999a0a80               
 li_buf = 0xffff0200125b7180

crash> xfs_buf.b_flags 0xffff0200125b7180 -x
 b_flags = 0x110032  (XBF_WRITE|XBF_ASYNC|XBF_DONE|_XBF_INODES|_XBF_PAGES) 

crash> xfs_buf.b_state 0xffff0200125b7180 -x
  b_state = 0x2 (XFS_BSTATE_IN_FLIGHT)

crash> xfs_buf.b_last_error,b_retries,b_first_retry_time 0xffff0200125b7180 -x
  b_last_error = 0x0
  b_retries = 0x0
  b_first_retry_time = 0x0 

The buf flags show the io had been done(XBF_DONE is set).
When I review the code xfs_buf_ioend, if XBF_DONE is set, xfs_buf_inode_iodone
will be called and it will remove the log item from ail list, then release the
xlog space by moving the tail_lsn.

But now this item is still in the ail list, and the b_last_error = 0, XBF_WRITE
is set.

xfs buf log item is the same as the inode log item.

crash> list -s xfs_log_item.li_buf 0xffff0340999a0a80
ffff033f8d7c9de8
  li_buf = 0x0
crash> xfs_buf_log_item.bli_buf  ffff033f8d7c9de8
  bli_buf = 0xffff0200125b4a80
crash> xfs_buf.b_flags 0xffff0200125b4a80 -x
  b_flags = 0x100032 (XBF_WRITE|XBF_ASYNC|XBF_DONE|_XBF_PAGES) 

I think it is impossible that (XBF_DONE is set & b_last_error = 0) and the item
still in the ail.

Is my analysis correct? 
Why xlog space cannot release space?

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