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Message-ID: <7bede423-690c-4f6a-9c23-def4ad08344e@amd.com>
Date: Tue, 18 Apr 2023 16:11:21 +0530
From: Vasant Hegde <vasant.hegde@....com>
To: Jerry Snitselaar <jsnitsel@...hat.com>,
Peng Zhang <zhangpeng.00@...edance.com>,
Robin Murphy <robin.murphy@....com>,
Joerg Roedel <joro@...tes.org>
Cc: will@...nel.org, iommu@...ts.linux.dev,
linux-kernel@...r.kernel.org, Li Bin <huawei.libin@...wei.com>,
Xie XiuQi <xiexiuqi@...wei.com>,
Yang Yingliang <yangyingliang@...wei.com>,
Suravee Suthikulpanit <suravee.suthikulpanit@....com>
Subject: Re: [PATCH] iommu: Avoid softlockup and rcu stall in
fq_flush_timeout().
Hi All,
On 4/11/2023 3:52 AM, Jerry Snitselaar wrote:
> On Thu, Feb 16, 2023 at 03:11:48PM +0800, Peng Zhang wrote:
>> There is softlockup under fio pressure test with smmu enabled:
>> watchdog: BUG: soft lockup - CPU#81 stuck for 22s! [swapper/81:0]
>> ...
>> Call trace:
>> fq_flush_timeout+0xc0/0x110
>> call_timer_fn+0x34/0x178
>> expire_timers+0xec/0x158
>> run_timer_softirq+0xc0/0x1f8
>> __do_softirq+0x120/0x324
>> irq_exit+0x11c/0x140
>> __handle_domain_irq+0x6c/0xc0
>> gic_handle_irq+0x6c/0x170
>> el1_irq+0xb8/0x140
>> arch_cpu_idle+0x38/0x1c0
>> default_idle_call+0x24/0x44
>> do_idle+0x1f4/0x2d8
>> cpu_startup_entry+0x2c/0x30
>> secondary_start_kernel+0x17c/0x1c8
>>
>> Rcu stall may also be triggered:
>>
>> rcu: INFO: rcu_sched self-detected stall on CPU
>> NMI backtrace for cpu 21
>> CPU: 21 PID: 118 Comm: ksoftirqd/21
>> ...
>> Call trace:
>> fq_flush_timeout+0x6d/0x90
>> ? fq_ring_free+0xc0/0xc0
>> call_timer_fn+0x2b/0x120
>> run_timer_softirq+0x1a6/0x420
>> ? finish_task_switch+0x80/0x280
>> __do_softirq+0xda/0x2da
>> ? sort_range+0x20/0x20
>> run_ksoftirqd+0x26/0x40
>> smpboot_thread_fn+0xb8/0x150
>> kthread+0x110/0x130
>> ? __kthread_cancel_work+0x40/0x40
>> ret_from_fork+0x1f/0x30
>>
>> This is because the timer callback fq_flush_timeout may run more than
>> 10ms, and timer may be processed continuously in the softirq so trigger
>> softlockup and rcu stall. We can use work to deal with fq_ring_free for
>> each cpu which may take long time, that to avoid triggering softlockup
>> and rcu stall.
>>
>> This patch is modified from the patch[1] of openEuler.
>>
>
> Hi Robin,
>
> I was looking at something similar to this recently were in this case
> they were beating the heck out the system with the hazard io stress
> test, and someone else with some medusa test tool. In one case they
> had them force a dump on the soft lockup. On the 384 core genoa, 90
> cores were spinning the iovad rb tree lock for one domain, 1 had it,
> and the poor flush queue timer handler was having to fight everyone
> for the lock. I'm not sure what would be considered a realistic workload
> compared to these stressors, but could this be an issue over time as
> systems continue to get more cores since the timer handler potentially
> grabs and releases the iova domain rb tree lock for each cpu? The only
> cases I know of are using io stressors, so I don't know how big a deal
> it is.
>
> I think soft lockups could still be produced with this patch, since
> there would still be the lock contention.
Right. We hit this issue when running stress-ng on 384 CPU system having NVMe
disk. I have tried this patch. This improved the situation. But we still hit
soft lockup after an hour or so.
Backtrace with this patch:
4551.470797] watchdog: BUG: soft lockup - CPU#328 stuck for 30s!
[kworker/328:1:2710]
[ 4551.479441] Modules linked in: nvme_fabrics(E) intel_rapl_msr(E)
intel_rapl_common(E) amd64_edac(E) edac_mce_amd(E) kvm_amd(E) kvm(E)
crct10dif_pclmul(E) ghash_clmulni_intel(E) sha512_ssse3(E) aesni_intel(E)
crypto_simd(E) cryptd(E) rapl(E) wmi_bmof(E) binfmt_misc(E) ipmi_ssif(E)
nls_iso8859_1(E) ast(E) drm_shmem_helper(E) drm_kms_helper(E) i2c_algo_bit(E)
syscopyarea(E) sysfillrect(E) sysimgblt(E) acpi_ipmi(E) ccp(E) k10temp(E)
ipmi_si(E) ipmi_devintf(E) ipmi_msghandler(E) mac_hid(E) sch_fq_codel(E) msr(E)
parport_pc(E) ppdev(E) lp(E) parport(E) ramoops(E) reed_solomon(E) pstore_blk(E)
pstore_zone(E) efi_pstore(E) drm(E) ip_tables(E) x_tables(E) autofs4(E)
crc32_pclmul(E) nvme(E) ahci(E) xhci_pci(E) tg3(E) nvme_core(E) libahci(E)
i2c_piix4(E) xhci_pci_renesas(E) wmi(E)
[ 4551.479475] CPU: 328 PID: 2710 Comm: kworker/328:1 Kdump: loaded Tainted: G
E 6.2.9schd_work+ #1
[ 4551.479477] Hardware name: AMD Corporation Genoa, BIOS RTI 03/20/2023
[ 4551.479479] Workqueue: events free_iova_work_func
[ 4551.479484] RIP: 0010:_raw_spin_unlock_irqrestore+0x21/0x60
[ 4551.479488] Code: 90 90 90 90 90 90 90 90 90 0f 1f 44 00 00 55 49 89 f0 48 89
e5 c6 07 00 0f 1f 00 41 f7 c0 00 02 00 00 74 06 fb 0f 1f 44 00 00 <65> ff 0d 50
f8 fc 7d 74 13 5d 31 c0 89 c2 89 c1 89 c6 89 c7 41 89
[ 4551.479489] RSP: 0018:ffa0000092e07e30 EFLAGS: 00000206
[ 4551.479491] RAX: 0000000000000000 RBX: 00000000000000f2 RCX: 0000000000000000
[ 4551.479492] RDX: 0000000000000000 RSI: 0000000000000282 RDI: ffd1ff3cf82be060
[ 4551.479492] RBP: ffa0000092e07e30 R08: 0000000000000282 R09: 0000000000000000
[ 4551.479493] R10: 0000000000000000 R11: 0000000000000000 R12: ff1100010d2af6d0
[ 4551.479493] R13: ffd1ff3cf82be060 R14: ffd1ff3cf82bb858 R15: 0000000000000282
[ 4551.479494] FS: 0000000000000000(0000) GS:ff11018056200000(0000)
knlGS:0000000000000000
[ 4551.479495] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[ 4551.479496] CR2: 00007ffd392f5f28 CR3: 0000000152f06004 CR4: 0000000000771ee0
[ 4551.479497] PKRU: 55555554
[ 4551.479497] Call Trace:
[ 4551.479498] <TASK>
[ 4551.479502] free_iova_work_func+0x6a/0xc0
[ 4551.479505] process_one_work+0x21f/0x440
[ 4551.479507] worker_thread+0x50/0x3f0
[ 4551.479509] ? __pfx_worker_thread+0x10/0x10
[ 4551.479510] kthread+0xee/0x120
[ 4551.479513] ? __pfx_kthread+0x10/0x10
[ 4551.479514] ret_from_fork+0x2c/0x50
[ 4551.479518] </TASK>
I did slight modification on top of this patch (schedule work on each CPU) and
it worked for me.
@Robin, Joerg,
Does something like below (schedule work on each CPU to free iova
(fq_ring_free()) is acceptable?
-Vasant
------
diff --git a/drivers/iommu/dma-iommu.c b/drivers/iommu/dma-iommu.c
index 7aed15e53f10..eb52814e67e5 100644
--- a/drivers/iommu/dma-iommu.c
+++ b/drivers/iommu/dma-iommu.c
@@ -157,10 +157,12 @@ static void fq_flush_iotlb(struct iommu_dma_cookie *cookie)
static void fq_flush_timeout(struct timer_list *t)
{
struct iommu_dma_cookie *cookie = from_timer(cookie, t, fq_timer);
+ int cpu;
atomic_set(&cookie->fq_timer_on, 0);
fq_flush_iotlb(cookie);
- schedule_work(&cookie->free_iova_work);
+ for_each_possible_cpu(cpu)
+ schedule_work_on(cpu, &cookie->free_iova_work);
}
static void queue_iova(struct iommu_dma_cookie *cookie,
@@ -235,17 +237,15 @@ static void free_iova_work_func(struct work_struct *work)
{
struct iommu_dma_cookie *cookie;
int cpu;
+ unsigned long flags;
+ struct iova_fq *fq;
cookie = container_of(work, struct iommu_dma_cookie, free_iova_work);
- for_each_possible_cpu(cpu) {
- unsigned long flags;
- struct iova_fq *fq;
+ fq = this_cpu_ptr(cookie->fq);
- fq = per_cpu_ptr(cookie->fq, cpu);
- spin_lock_irqsave(&fq->lock, flags);
- fq_ring_free(cookie, fq);
- spin_unlock_irqrestore(&fq->lock, flags);
- }
+ spin_lock_irqsave(&fq->lock, flags);
+ fq_ring_free(cookie, fq);
+ spin_unlock_irqrestore(&fq->lock, flags);
}
/* sysfs updates are serialised by the mutex of the group owning @domain */
---------
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