On Thu, Nov 19, 2015 at 7:03 PM, Dave Chinner <david@xxxxxxxxxxxxx> wrote:
> On Thu, Nov 19, 2015 at 04:18:13PM -0800, Dan Williams wrote:
>> Neither the filemap_fault() nor the xfs dax fault path is updating time.
>> This call leads to the following WARN() when the block device has been
>> torn down:
>
> I don't think that is right. In xfs_filemap_fault():
>
>
> ....
> /* DAX can shortcut the normal fault path on write faults! */
> if ((vmf->flags & FAULT_FLAG_WRITE) && IS_DAX(inode))
> return xfs_filemap_page_mkwrite(vma, vmf);
> ....
>
> And xfs_filemap_page_mkwrite() most definitely calls file_update_time():
>
> ....
> trace_xfs_filemap_page_mkwrite(XFS_I(inode));
>
> sb_start_pagefault(inode->i_sb);
> file_update_time(vma->vm_file);
> xfs_ilock(XFS_I(inode), XFS_MMAPLOCK_SHARED);
> ....
>
> And, finally, in xfs_filemap_pmd_fault():
>
> ....
> if (flags & FAULT_FLAG_WRITE) {
> sb_start_pagefault(inode->i_sb);
> file_update_time(vma->vm_file);
> }
> ....
>
> So we are clearly updating timestamps in XFS on every write fault
> that occurs, whether it be through ->page_mkwrite, ->fault or
> ->pmd_fault. Hence removing those from ext4 can't be the righ tthing
> to do.
>
Ah sorry I missed that. When I saw that xfs did not trigger the same
warning as ext4 I just assumed it wasn't doing the time update.
>>
>> WARNING: CPU: 0 PID: 2133 at fs/fs-writeback.c:2065 __mark_inode_dirty+0x261/0x350()
>> bdi-block not registered
> ^^^^^^^^^^^^^^^^^^^^^^^^
>> [..]
>> Call Trace:
>> [<ffffffff81459f62>] dump_stack+0x44/0x62
>> [<ffffffff810a2052>] warn_slowpath_common+0x82/0xc0
>> [<ffffffff810a20ec>] warn_slowpath_fmt+0x5c/0x80
>> [<ffffffff812831a1>] __mark_inode_dirty+0x261/0x350
>> [<ffffffff8126d109>] generic_update_time+0x79/0xd0
>> [<ffffffff8126d28d>] file_update_time+0xbd/0x110
>> [<ffffffff812e4bc8>] ext4_dax_fault+0x68/0x110
>> [<ffffffff811f816e>] __do_fault+0x4e/0xf0
>> [<ffffffff811fc2a7>] handle_mm_fault+0x5e7/0x1b50
>> [<ffffffff811fbd11>] ? handle_mm_fault+0x51/0x1b50
>> [<ffffffff810689c1>] __do_page_fault+0x191/0x3f0
>> [<ffffffff81068cef>] trace_do_page_fault+0x4f/0x120
>> [<ffffffff8106314a>] do_async_page_fault+0x1a/0xa0
>> [<ffffffff81902678>] async_page_fault+0x28/0x30
>
> Doesn't this indicate some problem at the block/bdi level?
> __mark_inode_dirty() should not throw warnings like this regardless
> of where it is called from...
>
I'll look closer at how the xfs path avoids triggering this...
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