[f2fs-dev] [Bug 208565] New: There may be dead lock for cp_rwsem during checkpoint

[bugzilla-daemon@bugzilla.kernel.org]

https://bugzilla.kernel.org/show_bug.cgi?id=208565

            Bug ID: 208565
           Summary: There may be dead lock for cp_rwsem during checkpoint
           Product: File System
           Version: 2.5
    Kernel Version: 4.14.181
          Hardware: All
                OS: Linux
              Tree: Mainline
            Status: NEW
          Severity: high
          Priority: P1
         Component: f2fs
          Assignee: filesystem_f2fs@kernel-bugs.kernel.org
          Reporter: Zhiguo.Niu@unisoc.com
        Regression: No

A deadlock may happens in the following scenario, backtrace is:

PID: 257    TASK: ecdd0000  CPU: 0   COMMAND: "init"
 #0 [<c0b420ec>] (__schedule) from [<c0b423c8>]
 #1 [<c0b423c8>] (schedule) from [<c0b459d4>]
 #2 [<c0b459d4>] (rwsem_down_read_failed) from [<c0b44fa0>]
 #3 [<c0b44fa0>] (down_read) from [<c044233c>]
 #4 [<c044233c>] (f2fs_truncate_blocks) from [<c0442890>]
 #5 [<c0442890>] (f2fs_truncate) from [<c044d408>]
 #6 [<c044d408>] (f2fs_evict_inode) from [<c030be18>]
 #7 [<c030be18>] (evict) from [<c030a558>]
 #8 [<c030a558>] (iput) from [<c047c600>]
 #9 [<c047c600>] (f2fs_sync_node_pages) from [<c0465414>]
#10 [<c0465414>] (f2fs_write_checkpoint) from [<c04575f4>]
#11 [<c04575f4>] (f2fs_sync_fs) from [<c0441918>]
#12 [<c0441918>] (f2fs_do_sync_file) from [<c0441098>]
#13 [<c0441098>] (f2fs_sync_file) from [<c0323fa0>]
#14 [<c0323fa0>] (vfs_fsync_range) from [<c0324294>]
#15 [<c0324294>] (do_fsync) from [<c0324014>]
#16 [<c0324014>] (sys_fsync) from [<c0108bc0>]

f2fs_sync_node_pages tries to flush dirty inode and calls iput(). This results
in deadlock as iput() tries to hold cp_rwsem, which is already held at the
beginning by checkpoint->block_operations().

There is a similar issue and patch in android.googlesource.com with commit id
is 82cc5e607b56abea4ea77023650247f5ae41b515, but the call trace is:

- f2fs_sync_node_pages()
 - if (is_inline_node(page))
>  - flush_inline_data()
   - ilookup()
     page = f2fs_pagecache_get_page()
     if (!page)
      goto iput_out;
     iput_out:
                        -close()
                        -iput()
       iput(inode);
       - f2fs_evict_inode()
        - f2fs_truncate_blocks()
         - f2fs_lock_op()
           - down_read(&sbi->cp_rwsem);

it seems than this patch has not cover current deadlock scenario, the current
deadlock call trace is:
- f2fs_sync_node_pages()

>  - if (flush_dirty_inode(page))

  - iput(inode);

       - f2fs_evict_inode()

        - f2fs_truncate_blocks()

         - f2fs_lock_op()

           - down_read(&sbi->cp_rwsem);

please help check and confirm.

thanks!

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