Messages in this thread Patch in this message | | | Date | Tue, 18 Apr 2023 16:11:21 +0530 | Subject | Re: [PATCH] iommu: Avoid softlockup and rcu stall in fq_flush_timeout(). | From | Vasant Hegde <> |
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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
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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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