On Fri, Feb 28, 2025 at 01:13:56PM +0100, Uladzislau Rezki (Sony) wrote: > Currently kvfree_rcu() APIs use a system workqueue which is > "system_unbound_wq" to driver RCU machinery to reclaim a memory. > > Recently, it has been noted that the following kernel warning can > be observed: > > <snip> > workqueue: WQ_MEM_RECLAIM nvme-wq:nvme_scan_work is flushing !WQ_MEM_RECLAIM events_unbound:kfree_rcu_work > WARNING: CPU: 21 PID: 330 at kernel/workqueue.c:3719 check_flush_dependency+0x112/0x120 > Modules linked in: intel_uncore_frequency(E) intel_uncore_frequency_common(E) skx_edac(E) ... > CPU: 21 UID: 0 PID: 330 Comm: kworker/u144:6 Tainted: G E 6.13.2-0_g925d379822da #1 > Hardware name: Wiwynn Twin Lakes MP/Twin Lakes Passive MP, BIOS YMM20 02/01/2023 > Workqueue: nvme-wq nvme_scan_work > RIP: 0010:check_flush_dependency+0x112/0x120 > Code: 05 9a 40 14 02 01 48 81 c6 c0 00 00 00 48 8b 50 18 48 81 c7 c0 00 00 00 48 89 f9 48 ... > RSP: 0018:ffffc90000df7bd8 EFLAGS: 00010082 > RAX: 000000000000006a RBX: ffffffff81622390 RCX: 0000000000000027 > RDX: 00000000fffeffff RSI: 000000000057ffa8 RDI: ffff88907f960c88 > RBP: 0000000000000000 R08: ffffffff83068e50 R09: 000000000002fffd > R10: 0000000000000004 R11: 0000000000000000 R12: ffff8881001a4400 > R13: 0000000000000000 R14: ffff88907f420fb8 R15: 0000000000000000 > FS: 0000000000000000(0000) GS:ffff88907f940000(0000) knlGS:0000000000000000 > CR2: 00007f60c3001000 CR3: 000000107d010005 CR4: 00000000007726f0 > PKRU: 55555554 > Call Trace: > <TASK> > ? __warn+0xa4/0x140 > ? check_flush_dependency+0x112/0x120 > ? report_bug+0xe1/0x140 > ? check_flush_dependency+0x112/0x120 > ? handle_bug+0x5e/0x90 > ? exc_invalid_op+0x16/0x40 > ? asm_exc_invalid_op+0x16/0x20 > ? timer_recalc_next_expiry+0x190/0x190 > ? check_flush_dependency+0x112/0x120 > ? check_flush_dependency+0x112/0x120 > __flush_work.llvm.1643880146586177030+0x174/0x2c0 > flush_rcu_work+0x28/0x30 > kvfree_rcu_barrier+0x12f/0x160 > kmem_cache_destroy+0x18/0x120 > bioset_exit+0x10c/0x150 > disk_release.llvm.6740012984264378178+0x61/0xd0 > device_release+0x4f/0x90 > kobject_put+0x95/0x180 > nvme_put_ns+0x23/0xc0 > nvme_remove_invalid_namespaces+0xb3/0xd0 > nvme_scan_work+0x342/0x490 > process_scheduled_works+0x1a2/0x370 > worker_thread+0x2ff/0x390 > ? pwq_release_workfn+0x1e0/0x1e0 > kthread+0xb1/0xe0 > ? __kthread_parkme+0x70/0x70 > ret_from_fork+0x30/0x40 > ? __kthread_parkme+0x70/0x70 > ret_from_fork_asm+0x11/0x20 > </TASK> > ---[ end trace 0000000000000000 ]--- > <snip> > > To address this switch to use of independent WQ_MEM_RECLAIM > workqueue, so the rules are not violated from workqueue framework > point of view. > > Apart of that, since kvfree_rcu() does reclaim memory it is worth > to go with WQ_MEM_RECLAIM type of wq because it is designed for > this purpose. > > Cc: <stable@xxxxxxxxxxxxxxx> > Cc: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx> > Cc: Keith Busch <kbusch@xxxxxxxxxx> > Closes: https://www.spinics.net/lists/kernel/msg5563270.html > Fixes: 6c6c47b063b5 ("mm, slab: call kvfree_rcu_barrier() from kmem_cache_destroy()"), > Reported-by: Keith Busch <kbusch@xxxxxxxxxx> > Signed-off-by: Uladzislau Rezki (Sony) <urezki@xxxxxxxxx> BTW, there is a path in RCU-tasks that involves queuing work on system_wq which is !WQ_RECLAIM. While I don't anticipate an issue such as the one fixed by this patch, I am wondering if we should move these to their own WQ_RECLAIM queues for added robustness since otherwise that will result in CB invocation (And thus memory freeing delays). Paul? kernel/rcu/tasks.h: queue_work_on(cpuwq, system_wq, &rtpcp_next->rtp_work); kernel/rcu/tasks.h: queue_work_on(cpuwq, system_wq, &rtpcp_next->rtp_work); For this patch: Reviewed-by: Joel Fernandes <joelagnelf@xxxxxxxxxx> thanks, - Joel > --- > mm/slab_common.c | 14 ++++++++++---- > 1 file changed, 10 insertions(+), 4 deletions(-) > > diff --git a/mm/slab_common.c b/mm/slab_common.c > index 4030907b6b7d..4c9f0a87f733 100644 > --- a/mm/slab_common.c > +++ b/mm/slab_common.c > @@ -1304,6 +1304,8 @@ module_param(rcu_min_cached_objs, int, 0444); > static int rcu_delay_page_cache_fill_msec = 5000; > module_param(rcu_delay_page_cache_fill_msec, int, 0444); > > +static struct workqueue_struct *rcu_reclaim_wq; > + > /* Maximum number of jiffies to wait before draining a batch. */ > #define KFREE_DRAIN_JIFFIES (5 * HZ) > #define KFREE_N_BATCHES 2 > @@ -1632,10 +1634,10 @@ __schedule_delayed_monitor_work(struct kfree_rcu_cpu *krcp) > if (delayed_work_pending(&krcp->monitor_work)) { > delay_left = krcp->monitor_work.timer.expires - jiffies; > if (delay < delay_left) > - mod_delayed_work(system_unbound_wq, &krcp->monitor_work, delay); > + mod_delayed_work(rcu_reclaim_wq, &krcp->monitor_work, delay); > return; > } > - queue_delayed_work(system_unbound_wq, &krcp->monitor_work, delay); > + queue_delayed_work(rcu_reclaim_wq, &krcp->monitor_work, delay); > } > > static void > @@ -1733,7 +1735,7 @@ kvfree_rcu_queue_batch(struct kfree_rcu_cpu *krcp) > // "free channels", the batch can handle. Break > // the loop since it is done with this CPU thus > // queuing an RCU work is _always_ success here. > - queued = queue_rcu_work(system_unbound_wq, &krwp->rcu_work); > + queued = queue_rcu_work(rcu_reclaim_wq, &krwp->rcu_work); > WARN_ON_ONCE(!queued); > break; > } > @@ -1883,7 +1885,7 @@ run_page_cache_worker(struct kfree_rcu_cpu *krcp) > if (rcu_scheduler_active == RCU_SCHEDULER_RUNNING && > !atomic_xchg(&krcp->work_in_progress, 1)) { > if (atomic_read(&krcp->backoff_page_cache_fill)) { > - queue_delayed_work(system_unbound_wq, > + queue_delayed_work(rcu_reclaim_wq, > &krcp->page_cache_work, > msecs_to_jiffies(rcu_delay_page_cache_fill_msec)); > } else { > @@ -2120,6 +2122,10 @@ void __init kvfree_rcu_init(void) > int i, j; > struct shrinker *kfree_rcu_shrinker; > > + rcu_reclaim_wq = alloc_workqueue("kvfree_rcu_reclaim", > + WQ_UNBOUND | WQ_MEM_RECLAIM, 0); > + WARN_ON(!rcu_reclaim_wq); > + > /* Clamp it to [0:100] seconds interval. */ > if (rcu_delay_page_cache_fill_msec < 0 || > rcu_delay_page_cache_fill_msec > 100 * MSEC_PER_SEC) { > -- > 2.39.5 >
