+CC Clark On 1/17/22 10:33, Sebastian Andrzej Siewior wrote: > On 2022-01-17 16:32:46 [+0800], Xin Long wrote: >> another issue. From the code analysis, this issue does exist on the >> upstream kernel, though I couldn't build an upstream RT kernel for the >> testing. > > This should also reproduce in v5.16 since the commit in question is > there. Yeah. I remember we had some issues with the commit during development, but I'd hope those were resolved and the commit that's ultimately merged got the fixes, see this subthread: https://lore.kernel.org/all/0b36128c-3e12-77df-85fe-a153a714569b@xxxxxxxxxxx/ >> > > CPU0 CPU1 >> > > ---- ---- >> > > cpus_read_lock() >> > > kn->active++ >> > > cpus_read_lock() [a] >> > > wait until kn->active == 0 >> > > >> > > Although cpu_hotplug_lock is a RWSEM, [a] will not block in there. But as >> > > lockdep annotations are added for cpu_hotplug_lock, a deadlock warning >> > > would be detected: > > The cpu_hotplug_lock is a per-CPU RWSEM. The lock in [a] will block if > there is a writer pending. > >> > > ====================================================== >> > > WARNING: possible circular locking dependency detected >> > > ------------------------------------------------------ >> > > dmsetup/1832 is trying to acquire lock: >> > > ffff986f5a0f9f20 (kn->count#144){++++}-{0:0}, at: kernfs_remove+0x1d/0x30 >> > > >> > > but task is already holding lock: >> > > ffffffffa43817c0 (slab_mutex){+.+.}-{3:3}, at: kmem_cache_destroy+0x2a/0x120 >> > > > > I tried to create & destroy a cryptarget which creates/destroy a cache > via bio_put_slab(). Either the callchain is different or something else > is but I didn't see a lockdep warning. RHEL-8 kernel seems to be 4.18, unless RT uses a newer one. Could be some silently relevant backport is missing? How about e.g. 59450bbc12be ("mm, slab, slub: stop taking cpu hotplug lock") ? > Sebastian
