On Tue, Nov 24, 2020 at 04:18:49PM -0500, Tejun Heo wrote: > Hello, > > Please see lkml.kernel.org/r/X708BTJ5njtbC2z1@xxxxxxxxxxxxxxx for a few nits > on the previous version. Thanks, I've addressed the mapping_set_gfp mask nit and updated the commit log. As Jan pointed also pointed out I think we do need the remove_inode_hash. > I might be confused but am wondering whether RCU is needed. It's currently > used to ensure that gendisk is accessible in the blkdev_get path but > wouldn't it be possible to simply pin gendisk from block_devices? The > gendisk and hd_structs hold the base refs of the block_devices and in turn > the block_devices pin the gendisk. When the gendisk gets deleted, it puts > the base refs of the block devices but stays around while the block devices > are being accessed. Yes, that sounds sensible. I'll take a look. > Also, would it make sense to separate out lookup_sem removal? I *think* it's > there to ensure that the same bdev doesn't get associated with old and new > gendisks at the same time but can't wrap my head around how it works > exactly. I can see that this may not be needed once the lifetimes of gendisk > and block_devices are tied together but that may warrant a bit more > explanation. Jan added lookup_sem in commit 56c0908c855afbb to prevent a three way race between del_gendisk and blkdev_open due to the weird bdev vs gendisk lifetime rules. None of that can happen with the new lookup scheme.
