Re: [core-for-CI][PATCH] iommu: Remove iova cpu hotplugging flushing

[Janusz Krzysztofik <janusz.krzysztofik@linux.intel.com>]

On Thursday, 22 September 2022 14:09:35 CEST Robin Murphy wrote:
> On 22/09/2022 11:10 am, Janusz Krzysztofik wrote:
> > From: Chris Wilson <chris@chris-wilson.co.uk>
> > 
> > Manual revert of commit f598a497bc7d ("iova: Add CPU hotplug handler to
> > flush rcaches").  It is trying to instantiate a cpuhp notifier from inside
> > a cpuhp callback.  That code replaced intel_iommu implementation of
> > flushing per-IOVA domain CPU rcaches which used a single instance of cpuhp
> > held for the module lifetime.
> 
> OK, *now* I see what's going on. It doesn't seem unreasonable to me for 
> bus notifiers to touch CPU hotplug - what seems more unexpected is the 
> coretemp driver creating and adding a platform device from inside a 
> hotplug callback.
> 
> Once we start trying to revert multiple unrelated bits of important 
> functionality from other subsystems because one driver is doing a weird 
> thing, maybe it's time to instead question whether that driver should be 
> doing a weird thing?

To be clear, the intention behind this revert was to unblock intel-gfx-ci, not 
to propose a solution.  I've CC-ed IOMMU and mainstream just for your 
awareness.

Thanks,
Janusz

> 
> Thanks,
> Robin.
> 
> > <4>[    6.928112] ======================================================
> > <4>[    6.928621] WARNING: possible circular locking dependency detected
> > <4>[    6.929225] 6.0.0-rc6-CI_DRM_12164-ga1f63e144e54+ #1 Not tainted
> > <4>[    6.929818] ------------------------------------------------------
> > <4>[    6.930415] cpuhp/0/15 is trying to acquire lock:
> > <4>[    6.931011] ffff888100e02a78 (&(&priv->bus_notifier)->rwsem){++++}-{3:3}, at: blocking_notifier_call_chain+0x20/0x50
> > <4>[    6.931533]
> >                    but task is already holding lock:
> > <4>[    6.931534] ffffffff826490c0 (cpuhp_state-up){+.+.}-{0:0}, at: cpuhp_thread_fun+0x48/0x1f0
> > <4>[    6.933069]
> >                    which lock already depends on the new lock.
> > 
> > <4>[    6.933070]
> >                    the existing dependency chain (in reverse order) is:
> > <4>[    6.933071]
> >                    -> #2 (cpuhp_state-up){+.+.}-{0:0}:
> > <4>[    6.933076]        lock_acquire+0xd3/0x310
> > <4>[    6.933079]        cpuhp_thread_fun+0xa6/0x1f0
> > <4>[    6.933082]        smpboot_thread_fn+0x1b5/0x260
> > <4>[    6.933084]        kthread+0xed/0x120
> > <4>[    6.933086]        ret_from_fork+0x1f/0x30
> > <4>[    6.933089]
> >                    -> #1 (cpu_hotplug_lock){++++}-{0:0}:
> > <4>[    6.933092]        lock_acquire+0xd3/0x310
> > <4>[    6.933094]        __cpuhp_state_add_instance+0x43/0x1c0
> > <4>[    6.933096]        iova_domain_init_rcaches+0x199/0x1c0
> > <4>[    6.933099]        iommu_setup_dma_ops+0x104/0x3d0
> > <4>[    6.933101]        iommu_probe_device+0xa4/0x180
> > <4>[    6.933103]        iommu_bus_notifier+0x2d/0x40
> > <4>[    6.933105]        notifier_call_chain+0x31/0x90
> > <4>[    6.933108]        blocking_notifier_call_chain+0x3a/0x50
> > <4>[    6.933110]        device_add+0x3c1/0x900
> > <4>[    6.933112]        pci_device_add+0x255/0x580
> > <4>[    6.933115]        pci_scan_single_device+0xa6/0xd0
> > <4>[    6.933117]        p2sb_bar+0x7f/0x220
> > <4>[    6.933120]        i801_add_tco_spt.isra.18+0x2b/0xca [i2c_i801]
> > <4>[    6.933124]        i801_add_tco+0xb1/0xfe [i2c_i801]
> > <4>[    6.933126]        i801_probe.cold.25+0xa9/0x3a7 [i2c_i801]
> > <4>[    6.933129]        pci_device_probe+0x95/0x110
> > <4>[    6.933132]        really_probe+0xd6/0x350
> > <4>[    6.933134]        __driver_probe_device+0x73/0x170
> > <4>[    6.933137]        driver_probe_device+0x1a/0x90
> > <4>[    6.933140]        __driver_attach+0xbc/0x190
> > <4>[    6.933141]        bus_for_each_dev+0x72/0xc0
> > <4>[    6.933143]        bus_add_driver+0x1bb/0x210
> > <4>[    6.933146]        driver_register+0x66/0xc0
> > <4>[    6.933147]        wmi_bmof_probe+0x3b/0xac [wmi_bmof]
> > <4>[    6.933150]        do_one_initcall+0x53/0x2f0
> > <4>[    6.933152]        do_init_module+0x45/0x1c0
> > <4>[    6.933154]        load_module+0x1cd5/0x1ec0
> > <4>[    6.933156]        __do_sys_finit_module+0xaf/0x120
> > <4>[    6.933158]        do_syscall_64+0x37/0x90
> > <4>[    6.933160]        entry_SYSCALL_64_after_hwframe+0x63/0xcd
> > <4>[    6.953757]
> >                    -> #0 (&(&priv->bus_notifier)->rwsem){++++}-{3:3}:
> > <4>[    6.953779]        validate_chain+0xb3f/0x2000
> > <4>[    6.953785]        __lock_acquire+0x5a4/0xb70
> > <4>[    6.953786]        lock_acquire+0xd3/0x310
> > <4>[    6.953787]        down_read+0x39/0x140
> > <4>[    6.953790]        blocking_notifier_call_chain+0x20/0x50
> > <4>[    6.953794]        device_add+0x3c1/0x900
> > <4>[    6.953797]        platform_device_add+0x108/0x240
> > <4>[    6.953799]        coretemp_cpu_online+0xe1/0x15e [coretemp]
> > <4>[    6.953805]        cpuhp_invoke_callback+0x181/0x8a0
> > <4>[    6.958244]        cpuhp_thread_fun+0x188/0x1f0
> > <4>[    6.958267]        smpboot_thread_fn+0x1b5/0x260
> > <4>[    6.958270]        kthread+0xed/0x120
> > <4>[    6.958272]        ret_from_fork+0x1f/0x30
> > <4>[    6.958274]
> >                    other info that might help us debug this:
> > 
> > <4>[    6.958275] Chain exists of:
> >                      &(&priv->bus_notifier)->rwsem --> cpu_hotplug_lock --> cpuhp_state-up
> > 
> > <4>[    6.961037]  Possible unsafe locking scenario:
> > 
> > <4>[    6.961038]        CPU0                    CPU1
> > <4>[    6.961038]        ----                    ----
> > <4>[    6.961039]   lock(cpuhp_state-up);
> > <4>[    6.961040]                                lock(cpu_hotplug_lock);
> > <4>[    6.961041]                                lock(cpuhp_state-up);
> > <4>[    6.961042]   lock(&(&priv->bus_notifier)->rwsem);
> > <4>[    6.961044]
> >                     *** DEADLOCK ***
> > 
> > <4>[    6.961044] 2 locks held by cpuhp/0/15:
> > <4>[    6.961046]  #0: ffffffff82648f10 (cpu_hotplug_lock){++++}-{0:0}, at: cpuhp_thread_fun+0x48/0x1f0
> > <4>[    6.961053]  #1: ffffffff826490c0 (cpuhp_state-up){+.+.}-{0:0}, at: cpuhp_thread_fun+0x48/0x1f0
> > <4>[    6.961058]
> >                    stack backtrace:
> > <4>[    6.961059] CPU: 0 PID: 15 Comm: cpuhp/0 Not tainted 6.0.0-rc6-CI_DRM_12164-ga1f63e144e54+ #1
> > <4>[    6.961062] Hardware name: Intel Corporation NUC8i7HVK/NUC8i7HVB, BIOS HNKBLi70.86A.0047.2018.0718.1706 07/18/2018
> > <4>[    6.961063] Call Trace:
> > <4>[    6.961064]  <TASK>
> > <4>[    6.961065]  dump_stack_lvl+0x56/0x7f
> > <4>[    6.961069]  check_noncircular+0x132/0x150
> > <4>[    6.961078]  validate_chain+0xb3f/0x2000
> > <4>[    6.961083]  __lock_acquire+0x5a4/0xb70
> > <4>[    6.961087]  lock_acquire+0xd3/0x310
> > <4>[    6.961088]  ? blocking_notifier_call_chain+0x20/0x50
> > <4>[    6.961093]  down_read+0x39/0x140
> > <4>[    6.961097]  ? blocking_notifier_call_chain+0x20/0x50
> > <4>[    6.961099]  blocking_notifier_call_chain+0x20/0x50
> > <4>[    6.961102]  device_add+0x3c1/0x900
> > <4>[    6.961106]  ? dev_set_name+0x4e/0x70
> > <4>[    6.961109]  platform_device_add+0x108/0x240
> > <4>[    6.961112]  coretemp_cpu_online+0xe1/0x15e [coretemp]
> > <4>[    6.961117]  ? create_core_data+0x550/0x550 [coretemp]
> > <4>[    6.961120]  cpuhp_invoke_callback+0x181/0x8a0
> > <4>[    6.961124]  cpuhp_thread_fun+0x188/0x1f0
> > <4>[    6.961129]  ? smpboot_thread_fn+0x1e/0x260
> > <4>[    6.961131]  smpboot_thread_fn+0x1b5/0x260
> > <4>[    6.961134]  ? sort_range+0x20/0x20
> > <4>[    6.961135]  kthread+0xed/0x120
> > <4>[    6.961137]  ? kthread_complete_and_exit+0x20/0x20
> > <4>[    6.961139]  ret_from_fork+0x1f/0x30
> > <4>[    6.961145]  </TASK>
> > 
> > Closes: https://gitlab.freedesktop.org/drm/intel/issues/6641
> > Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
> > Signed-off-by: Janusz Krzysztofik <janusz.krzysztofik@linux.intel.com>
> > ---
> >   drivers/iommu/iova.c       | 28 ----------------------------
> >   include/linux/cpuhotplug.h |  1 -
> >   include/linux/iova.h       |  1 -
> >   3 files changed, 30 deletions(-)
> > 
> > diff --git a/drivers/iommu/iova.c b/drivers/iommu/iova.c
> > index 47d1983dfa2a4..f0136d0231f06 100644
> > --- a/drivers/iommu/iova.c
> > +++ b/drivers/iommu/iova.c
> > @@ -31,16 +31,6 @@ unsigned long iova_rcache_range(void)
> >   	return PAGE_SIZE << (IOVA_RANGE_CACHE_MAX_SIZE - 1);
> >   }
> >   
> > -static int iova_cpuhp_dead(unsigned int cpu, struct hlist_node *node)
> > -{
> > -	struct iova_domain *iovad;
> > -
> > -	iovad = hlist_entry_safe(node, struct iova_domain, cpuhp_dead);
> > -
> > -	free_cpu_cached_iovas(cpu, iovad);
> > -	return 0;
> > -}
> > -
> >   static void free_global_cached_iovas(struct iova_domain *iovad);
> >   
> >   static struct iova *to_iova(struct rb_node *node)
> > @@ -255,21 +245,10 @@ int iova_cache_get(void)
> >   {
> >   	mutex_lock(&iova_cache_mutex);
> >   	if (!iova_cache_users) {
> > -		int ret;
> > -
> > -		ret = cpuhp_setup_state_multi(CPUHP_IOMMU_IOVA_DEAD, "iommu/iova:dead", NULL,
> > -					iova_cpuhp_dead);
> > -		if (ret) {
> > -			mutex_unlock(&iova_cache_mutex);
> > -			pr_err("Couldn't register cpuhp handler\n");
> > -			return ret;
> > -		}
> > -
> >   		iova_cache = kmem_cache_create(
> >   			"iommu_iova", sizeof(struct iova), 0,
> >   			SLAB_HWCACHE_ALIGN, NULL);
> >   		if (!iova_cache) {
> > -			cpuhp_remove_multi_state(CPUHP_IOMMU_IOVA_DEAD);
> >   			mutex_unlock(&iova_cache_mutex);
> >   			pr_err("Couldn't create iova cache\n");
> >   			return -ENOMEM;
> > @@ -292,7 +271,6 @@ void iova_cache_put(void)
> >   	}
> >   	iova_cache_users--;
> >   	if (!iova_cache_users) {
> > -		cpuhp_remove_multi_state(CPUHP_IOMMU_IOVA_DEAD);
> >   		kmem_cache_destroy(iova_cache);
> >   	}
> >   	mutex_unlock(&iova_cache_mutex);
> > @@ -495,8 +473,6 @@ EXPORT_SYMBOL_GPL(free_iova_fast);
> >   
> >   static void iova_domain_free_rcaches(struct iova_domain *iovad)
> >   {
> > -	cpuhp_state_remove_instance_nocalls(CPUHP_IOMMU_IOVA_DEAD,
> > -					    &iovad->cpuhp_dead);
> >   	free_iova_rcaches(iovad);
> >   }
> >   
> > @@ -755,10 +731,6 @@ int iova_domain_init_rcaches(struct iova_domain *iovad)
> >   		}
> >   	}
> >   
> > -	ret = cpuhp_state_add_instance_nocalls(CPUHP_IOMMU_IOVA_DEAD,
> > -					       &iovad->cpuhp_dead);
> > -	if (ret)
> > -		goto out_err;
> >   	return 0;
> >   
> >   out_err:
> > diff --git a/include/linux/cpuhotplug.h b/include/linux/cpuhotplug.h
> > index f61447913db97..8f541a6b63e41 100644
> > --- a/include/linux/cpuhotplug.h
> > +++ b/include/linux/cpuhotplug.h
> > @@ -95,7 +95,6 @@ enum cpuhp_state {
> >   	CPUHP_PAGE_ALLOC,
> >   	CPUHP_NET_DEV_DEAD,
> >   	CPUHP_PCI_XGENE_DEAD,
> > -	CPUHP_IOMMU_IOVA_DEAD,
> >   	CPUHP_LUSTRE_CFS_DEAD,
> >   	CPUHP_AP_ARM_CACHE_B15_RAC_DEAD,
> >   	CPUHP_PADATA_DEAD,
> > diff --git a/include/linux/iova.h b/include/linux/iova.h
> > index c6ba6d95d79c2..fd77cd5bfa333 100644
> > --- a/include/linux/iova.h
> > +++ b/include/linux/iova.h
> > @@ -37,7 +37,6 @@ struct iova_domain {
> >   	struct iova	anchor;		/* rbtree lookup anchor */
> >   
> >   	struct iova_rcache	*rcaches;
> > -	struct hlist_node	cpuhp_dead;
> >   };
> >   
> >   static inline unsigned long iova_size(struct iova *iova)
>