Re: [PATCH v7 07/22] Replace the XIP page fault handler with the DAX page fault handler

[Matthew Wilcox <willy@linux.intel.com>]

On Tue, Jul 29, 2014 at 11:04:57PM +0200, Jan Kara wrote:
> > Path 1:
> > 
> > ext4_fallocate ->
> >  ext4_punch_hole ->
> >   ext4_inode_attach_jinode() -> ... ->
> >     lock_map_acquire(&handle->h_lockdep_map);
> >   truncate_pagecache_range() ->
> >    unmap_mapping_range() ->
> >     mutex_lock(&mapping->i_mmap_mutex);
>   This is strange. I don't see how ext4_inode_attach_jinode() can ever lead
> to lock_map_acquire(&handle->h_lockdep_map). Can you post a full trace for
> this?

Unfortunately, lockdep finds the inversion in the other order, so I
have the backtraces of this path hitting the i_mmap_mutex while already
holding jbd_mutex:

 ======================================================
 [ INFO: possible circular locking dependency detected ]
 3.16.0-rc6+ #91 Tainted: G        W    
 -------------------------------------------------------
 fstest/31836 is trying to acquire lock:
  (jbd2_handle){+.+.+.}, at: [<ffffffffa00f5333>] start_this_handle+0x193/0x630 [jbd2]
 
 but task is already holding lock:
  (&mapping->i_mmap_mutex){+.+...}, at: [<ffffffff8124c0a0>] do_dax_fault+0x4e0/0x640
 
 which lock already depends on the new lock.
 
 
 the existing dependency chain (in reverse order) is:
 
 -> #1 (&mapping->i_mmap_mutex){+.+...}:
        [<ffffffff810cfa22>] lock_acquire+0xb2/0x1f0
        [<ffffffff815cad15>] mutex_lock_nested+0x75/0x420
        [<ffffffff811acf4b>] unmap_mapping_range+0x6b/0x180
        [<ffffffff811901ba>] truncate_pagecache_range+0x4a/0x60
        [<ffffffffa020af41>] ext4_punch_hole+0x4d1/0x530 [ext4]
        [<ffffffffa0235356>] ext4_fallocate+0x156/0xb70 [ext4]
        [<ffffffff811f3c19>] do_fallocate+0x119/0x1b0
        [<ffffffff811f3cf3>] SyS_fallocate+0x43/0x70
        [<ffffffff815cf8a9>] system_call_fastpath+0x16/0x1b
 
 -> #0 (jbd2_handle){+.+.+.}:
        [<ffffffff810ce9e1>] __lock_acquire+0x1d01/0x1eb0
        [<ffffffff810cfa22>] lock_acquire+0xb2/0x1f0
        [<ffffffffa00f538e>] start_this_handle+0x1ee/0x630 [jbd2]
        [<ffffffffa00f5c04>] jbd2__journal_start+0xd4/0x260 [jbd2]
        [<ffffffffa0235f6d>] __ext4_journal_start_sb+0x6d/0x190 [ext4]
        [<ffffffffa0206fca>] _ext4_get_block+0x16a/0x1c0 [ext4]
        [<ffffffffa0207036>] ext4_get_block+0x16/0x20 [ext4]
        [<ffffffff8124c199>] do_dax_fault+0x5d9/0x640
        [<ffffffff8124c23f>] dax_fault+0x3f/0x90
        [<ffffffffa01ff975>] ext4_dax_fault+0x15/0x20 [ext4]
        [<ffffffff811ab6d1>] __do_fault+0x41/0xd0
        [<ffffffff811ae7f5>] do_shared_fault.isra.56+0x35/0x220
        [<ffffffff811af983>] handle_mm_fault+0x303/0xf70
        [<ffffffff81062d2c>] __do_page_fault+0x1ec/0x5b0
        [<ffffffff81063112>] do_page_fault+0x22/0x30
        [<ffffffff815d18b8>] page_fault+0x28/0x30
 
 other info that might help us debug this:
 
  Possible unsafe locking scenario:
 
        CPU0                    CPU1
        ----                    ----
   lock(&mapping->i_mmap_mutex);
                                lock(jbd2_handle);
                                lock(&mapping->i_mmap_mutex);
   lock(jbd2_handle);
 
  *** DEADLOCK ***
 
 3 locks held by fstest/31836:
  #0:  (&mm->mmap_sem){++++++}, at: [<ffffffff81062cc2>] __do_page_fault+0x182/0x5b0
  #1:  (sb_pagefaults){++++..}, at: [<ffffffff8124c27a>] dax_fault+0x7a/0x90
  #2:  (&mapping->i_mmap_mutex){+.+...}, at: [<ffffffff8124c0a0>] do_dax_fault+0x4e0/0x640
 
 stack backtrace:
 CPU: 6 PID: 31836 Comm: fstest Tainted: G        W     3.16.0-rc6+ #91
 Hardware name: Gigabyte Technology Co., Ltd. To be filled by O.E.M./Q87M-D2H, BIOS F6 08/03/2013
  ffffffff825e63e0 ffff8800a0fc78c0 ffffffff815c6bc3 ffffffff825e63e0
  ffff8800a0fc7900 ffffffff815c4e59 ffff8800a0fc7970 ffff8800a88f4a50
  ffff8800a88f4af8 ffff8800a88f5280 0000000000000003 ffff8800a88f5248
 Call Trace:
  [<ffffffff815c6bc3>] dump_stack+0x4d/0x66
  [<ffffffff815c4e59>] print_circular_bug+0x201/0x20f
  [<ffffffff810ce9e1>] __lock_acquire+0x1d01/0x1eb0
  [<ffffffff81023b00>] ? cyc2ns_read_end+0x20/0x20
  [<ffffffff810cfa22>] lock_acquire+0xb2/0x1f0
  [<ffffffffa00f5333>] ? start_this_handle+0x193/0x630 [jbd2]
  [<ffffffffa00f538e>] start_this_handle+0x1ee/0x630 [jbd2]
  [<ffffffffa00f5333>] ? start_this_handle+0x193/0x630 [jbd2]
  [<ffffffffa00f5020>] ? new_handle+0x20/0x60 [jbd2]
  [<ffffffffa00f5c04>] jbd2__journal_start+0xd4/0x260 [jbd2]
  [<ffffffffa0206fca>] ? _ext4_get_block+0x16a/0x1c0 [ext4]
  [<ffffffffa0235f6d>] __ext4_journal_start_sb+0x6d/0x190 [ext4]
  [<ffffffffa0206fca>] _ext4_get_block+0x16a/0x1c0 [ext4]
  [<ffffffffa0207036>] ext4_get_block+0x16/0x20 [ext4]
  [<ffffffff8124c199>] do_dax_fault+0x5d9/0x640
  [<ffffffffa0207020>] ? _ext4_get_block+0x1c0/0x1c0 [ext4]
  [<ffffffffa0207020>] ? _ext4_get_block+0x1c0/0x1c0 [ext4]
  [<ffffffff8124c23f>] dax_fault+0x3f/0x90
  [<ffffffffa01ff975>] ext4_dax_fault+0x15/0x20 [ext4]
  [<ffffffff811ab6d1>] __do_fault+0x41/0xd0
  [<ffffffff811ae7f5>] do_shared_fault.isra.56+0x35/0x220
  [<ffffffff811af983>] handle_mm_fault+0x303/0xf70
  [<ffffffff810ca676>] ? __lock_is_held+0x56/0x80
  [<ffffffff81062d2c>] __do_page_fault+0x1ec/0x5b0
  [<ffffffff8119dc3c>] ? vm_mmap_pgoff+0x9c/0xc0
  [<ffffffff810c80cf>] ? up_write+0x1f/0x40
  [<ffffffff8119dc3c>] ? vm_mmap_pgoff+0x9c/0xc0
  [<ffffffff8133e1ea>] ? trace_hardirqs_off_thunk+0x3a/0x3c
  [<ffffffff81063112>] do_page_fault+0x22/0x30
  [<ffffffff815d18b8>] page_fault+0x28/0x30