On 9/19/22 18:39, Maurizio Lombardi wrote:
> Commit 5a836bf6b09f ("mm: slub: move flush_cpu_slab() invocations
> __free_slab() invocations out of IRQ context") moved all flush_cpu_slab()
> invocations to the global workqueue to avoid a problem related
> with deactivate_slab()/__free_slab() being called from an IRQ context
> on PREEMPT_RT kernels.
>
> When the flush_all_cpu_locked() function is called from a task context
> it may happen that a workqueue with WQ_MEM_RECLAIM bit set ends up
> flushing the global workqueue, this will cause a dependency issue.
>
> workqueue: WQ_MEM_RECLAIM nvme-delete-wq:nvme_delete_ctrl_work [nvme_core]
> is flushing !WQ_MEM_RECLAIM events:flush_cpu_slab
> WARNING: CPU: 37 PID: 410 at kernel/workqueue.c:2637
> check_flush_dependency+0x10a/0x120
> Workqueue: nvme-delete-wq nvme_delete_ctrl_work [nvme_core]
> RIP: 0010:check_flush_dependency+0x10a/0x120[ 453.262125] Call Trace:
> __flush_work.isra.0+0xbf/0x220
> ? __queue_work+0x1dc/0x420
> flush_all_cpus_locked+0xfb/0x120
> __kmem_cache_shutdown+0x2b/0x320
> kmem_cache_destroy+0x49/0x100
> bioset_exit+0x143/0x190
> blk_release_queue+0xb9/0x100
> kobject_cleanup+0x37/0x130
> nvme_fc_ctrl_free+0xc6/0x150 [nvme_fc]
> nvme_free_ctrl+0x1ac/0x2b0 [nvme_core]
>
> Fix this bug by creating a workqueue for the flush operation with
> the WQ_MEM_RECLAIM bit set.
>
> v2: Create a workqueue with WQ_MEM_RECLAIM
> instead of trying to revert the changes.
>
> v3: replace create_workqueue() with alloc_workqueue() and BUG_ON() with
> WARN_ON()
>
> Signed-off-by: Maurizio Lombardi <[email protected]>
Thanks, I added a Fixes: and Cc stable as AFAICS the warnings are not under
a debugging config option, and it could bite somebody near OOM. Added to
slab.git for-6.0/fixes and will include in pullrq this week.