> On 13 Oct 2017, at 17.35, Rakesh Pandit <rak...@tuxera.com> wrote: > >> On Fri, Oct 13, 2017 at 07:58:09AM -0700, Christoph Hellwig wrote: >>> On Fri, Oct 13, 2017 at 02:45:51PM +0200, Matias Bjørling wrote: >>> From: Rakesh Pandit <rak...@tuxera.com> >>> >>> When a virtual block device is formatted and mounted after creating >>> with "nvme lnvm create... -t pblk", a removal from "nvm lnvm remove" >>> would result in this: >>> >>> 446416.309757] bdi-block not registered >>> [446416.309773] ------------[ cut here ]------------ >>> [446416.309780] WARNING: CPU: 3 PID: 4319 at fs/fs-writeback.c:2159 >>> __mark_inode_dirty+0x268/0x340 >>> >>> Ideally removal should return -EBUSY as block device is mounted after >>> formatting. This patch tries to address this checking if whole device >>> or any partition of it already mounted or not before removal. >> >> How is this different from any other block device that can be >> removed even if a file system is mounted? > > One can create many virtual block devices on top of physical using: > nvme lnvm create ... -t pblk > > And remove them using: > nvme lnvm remove > > Because the block devices are virtual in nature created by a program I was > expecting removal to tell me they are busy instead of bdi-block not registered > following by a WARNING (above). My use case was writing automatic test case > but I assumed this is useful in general. > >> >>> >>> Whole device is checked using "bd_super" member of block device. This >>> member is always set once block device has been mounted using a >>> filesystem. Another member "bd_part_count" takes care of checking any >>> if any partitions are under use. "bd_part_count" is only updated >>> under locks when partitions are opened or closed (first open and last >>> release). This at least does take care sending -EBUSY if removal is >>> being attempted while whole block device or any partition is mounted. >>> >> >> That's a massive layering violation, and a driver has no business >> looking at these fields. > > Okay, I didn't consider this earlier. I would suggest a revert for this.
The use case is still valid, since a block device typically does not disappear under a file system - at least not because of a script suddenly removing it by mistake. Any suggestion on how we can do this better? Javier.
