Re: [PATCH v2 6/7] mm, slab: call kvfree_rcu_barrier() from kmem_cache_destroy()

Mateusz Guzik
2025-02-21T16:51:52Z

On Fri, Feb 21, 2025 at 5:30 PM Keith Busch <kbusch@kernel.org> wrote:
> This patch appears to be triggering a new warning in certain conditions
> when tearing down an nvme namespace's block device. Stack trace is at
> the end.
>
> The warning indicates that this shouldn't be called from a
> WQ_MEM_RECLAIM workqueue. This workqueue is responsible for bringing up
> and tearing down block devices, so this is a memory reclaim use AIUI.
> I'm a bit confused why we can't tear down a disk from within a memory
> reclaim workqueue. Is the recommended solution to simply remove the WQ
> flag when creating the workqueue?
>

This ends up calling into bioset_exit -> bio_put_slab -> kmem_cache_destroy

Sizes of the bio- slabs are off the beaten path, so it may be they
make sense to exist.

With the assumption that caches should be there, this can instead
invoke kmem_cache_destroy from a queue where it is safe to do it. This
is not supposed to be a frequent operation.
--
Mateusz Guzik <mjguzik gmail.com>