9:23 p.m.
On Mon, Jan 04, 2016 at 10:20:16AM -0800, Dan Williams wrote:
This warning was added as a debugging aid way back in commit
500b067c5e6c "writeback: check for registered bdi in flusher add and
inode dirty" when we were switching over to per-bdi writeback.
Once the block device has been torn down it's no longer useful to
complain about unregistered bdi's. Clear the writeback capability under
the the wb->list_lock(), so that __mark_inode_dirty has no opportunity
to race bdi_unregister() to this WARN() condition.
Alternatively we could just delete the warning...
The warning is correct - the filesytem is trying to mark an inode
dirty on a device that can't do writeback anymore. Seems to me like
it is functioning as it should.
Found this while testing block device remove from underneath an
active
fs triggering traces like:
WARNING: CPU: 6 PID: 2129 at fs/fs-writeback.c:2065 __mark_inode_dirty+0x261/0x350()
bdi-block not registered
[..]
Call Trace:
[<ffffffff81459f02>] dump_stack+0x44/0x62
[<ffffffff810a1f32>] warn_slowpath_common+0x82/0xc0
[<ffffffff810a1fcc>] warn_slowpath_fmt+0x5c/0x80
[<ffffffff812830b1>] __mark_inode_dirty+0x261/0x350
[<ffffffff8126d019>] generic_update_time+0x79/0xd0
[<ffffffff8126d19d>] file_update_time+0xbd/0x110
[<ffffffff812e4ab8>] ext4_dax_fault+0x68/0x110
[<ffffffff811f7f3e>] __do_fault+0x4e/0xf0
This seems like the problem to me - you haven't implemented a
shutdown hook for ext4, and so it continues to allow page faults to
make progress after the device has been removed. The DAX fault
should have been failed before the filesystem gets to the point of
marking the inode dirty....
+ /* tell __mark_inode_dirty that writeback is no longer possible */
+ spin_lock(&wb->list_lock);
+ wb->bdi->capabilities |= BDI_CAP_NO_WRITEBACK;
+ spin_unlock(&wb->list_lock);
+
spin_unlock_bh(&wb->work_lock);
Is that lock ordering safe? i.e. it's inside a section using bh-safe
locking, which tends to imply that it can run from interrupt
contexts. Can we get something like
spin_lock(&wb->list_lock);
.....
<irq>
.....
wb_shutdown
spin_lock_bh(&wb->work_lock);
spin_lock(&wb->list_lock);
Cheers,
Dave.
--
Dave Chinner
david(a)fromorbit.com