[PATCH 5.19 063/207] mm: slub: fix flush_cpu_slab()/__free_slab() invocations in task context.

Greg Kroah-Hartman
2022-09-26T11:39:41Z

From: Maurizio Lombardi <mlombard@redhat.com>

commit e45cc288724f0cfd497bb5920bcfa60caa335729 upstream.

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.

Fixes: 5a836bf6b09f ("mm: slub: move flush_cpu_slab() invocations __free_slab() invocations out of IRQ context")
Cc: <stable@vger.kernel.org>
Signed-off-by: Maurizio Lombardi <mlombard@redhat.com>
Reviewed-by: Hyeonggon Yoo <42.hyeyoo@gmail.com>
Signed-off-by: Vlastimil Babka <vbabka@suse.cz>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
mm/slub.c | 9 ++++++++-
1 file changed, 8 insertions(+), 1 deletion(-)

--- a/mm/slub.c
+++ b/mm/slub.c
@@ -310,6 +310,11 @@ static inline void stat(const struct kme
*/
static nodemask_t slab_nodes;

+/*
+ * Workqueue used for flush_cpu_slab().
+ */
+static struct workqueue_struct *flushwq;
+
/********************************************************************
* Core slab cache functions
*******************************************************************/
@@ -2730,7 +2735,7 @@ static void flush_all_cpus_locked(struct
INIT_WORK(&sfw->work, flush_cpu_slab);
sfw->skip = false;
sfw->s = s;
- schedule_work_on(cpu, &sfw->work);
+ queue_work_on(cpu, flushwq, &sfw->work);
}

for_each_online_cpu(cpu) {
@@ -4880,6 +4885,8 @@ void __init kmem_cache_init(void)

void __init kmem_cache_init_late(void)
{
+ flushwq = alloc_workqueue("slub_flushwq", WQ_MEM_RECLAIM, 0);
+ WARN_ON(!flushwq);
}

struct kmem_cache *