On Thu, Apr 27, 2023 at 10:20:28AM +0800, Ming Lei wrote: > Hello Guys, > > I got one report in which buffered write IO hangs in balance_dirty_pages, > after one nvme block device is unplugged physically, then umount can't > succeed. > > Turns out it is one long-term issue, and it can be triggered at least > since v5.14 until the latest v6.3. > > And the issue can be reproduced reliably in KVM guest: > > 1) run the following script inside guest: > > mkfs.ext4 -F /dev/nvme0n1 > mount /dev/nvme0n1 /mnt > dd if=/dev/zero of=/mnt/z.img& > sleep 10 > echo 1 > /sys/block/nvme0n1/device/device/remove > > 2) dd hang is observed and /dev/nvme0n1 is gone actually Sorry to jump in so late. For an ungraceful nvme removal, like a surpirse hot unplug, the driver sets the capacity to 0 and that effectively ends all dirty page writers that could stall forward progress on the removal. And that 0 capacity should also cause 'dd' to exit. But this is not an ungraceful removal, so we're not getting that forced behavior. Could we use the same capacity trick here after flushing any outstanding dirty pages?
