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...
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
[<ffffffff811fc077>] handle_mm_fault+0x5e7/0x1b50
[<ffffffff811fbae1>] ? handle_mm_fault+0x51/0x1b50
[<ffffffff81068981>] __do_page_fault+0x191/0x3f0
[<ffffffff81068caf>] trace_do_page_fault+0x4f/0x120
[<ffffffff810630fa>] do_async_page_fault+0x1a/0xa0
[<ffffffff819023f8>] async_page_fault+0x28/0x30
Cc: Jan Kara <jack@xxxxxxxx>
Cc: Tejun Heo <tj@xxxxxxxxxx>
Cc: Jens Axboe <axboe@xxxxxx>
Cc: Dave Chinner <david@xxxxxxxxxxxxx>
Signed-off-by: Dan Williams <dan.j.williams@xxxxxxxxx>
---
mm/backing-dev.c | 7 +++++++
1 file changed, 7 insertions(+)
diff --git a/mm/backing-dev.c b/mm/backing-dev.c
index 7340353f8aea..9ea843bca709 100644
--- a/mm/backing-dev.c
+++ b/mm/backing-dev.c
@@ -343,10 +343,17 @@ static void wb_shutdown(struct bdi_writeback *wb)
{
/* Make sure nobody queues further work */
spin_lock_bh(&wb->work_lock);
+
if (!test_and_clear_bit(WB_registered, &wb->state)) {
spin_unlock_bh(&wb->work_lock);
return;
}
+
+ /* 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);
/*
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