Messages in this thread | | | Date | Mon, 17 Jan 2022 10:33:59 +0100 | From | Sebastian Andrzej Siewior <> | Subject | Re: [PATCH] mm: slub: fix a deadlock warning in kmem_cache_destroy |
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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.
> > > 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.
Sebastian
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