Re: [PATCH 45/46] mm/memory-tiers: unregister empty tiers outside memory_tier_lock

[Gregory Price]

On 2026-10-27 00:18 +0100, David Hildenbrand (Arm) wrote:
> When offlining a node's last memory empties its tier,
> clear_node_memory_tier() calls device_unregister() while holding
> memory_tier_lock. A concurrent sysfs read can hold a kernfs active
> reference and block in nodelist_show() on that mutex. device_unregister()
> then waits in kernfs_drain() for the read to finish and release its active
> reference, while the reader waits for the offlining task to release the
> mutex.
> 
> Return the node's former tier from clear_node_memory_tier(), making the
> helper more similar to set_node_memory_tier(), which also returns a
> memory_tier pointer. Let the caller unlink an empty tier under
> memory_tier_lock before rebuilding demotion targets, then unregister its
> device after dropping the lock.
> 
> Fixes: 9832fb87834e ("mm/demotion: expose memory tier details via sysfs")
> Cc: stable@xxxxxxxxxxxxxxx
> Reported-by: Josef Bacik <josef@xxxxxxxxxxxxxx>
> Signed-off-by: David Hildenbrand (Arm) <david@xxxxxxxxxx>

Reviewed-by: Gregory Price (Meta) <gourry@xxxxxxxxxx>

-- 
Gregory Price (Meta) <gourry@xxxxxxxxxx>