[PATCH v1 2/2] mm/slab/kvfree_rcu: Switch to WQ_MEM_RECLAIM wq
From: Uladzislau Rezki (Sony)
Date: Fri Feb 28 2025 - 07:15:12 EST
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>
---
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