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From: Thomas Gleixner <tglx@linutronix.de>
To: Ricardo Neri <ricardo.neri-calderon@linux.intel.com>
Cc: Kate Stewart <kstewart@linuxfoundation.org>,
	Peter Zijlstra <peterz@infradead.org>,
	Jan Kiszka <jan.kiszka@siemens.com>,
	Ricardo Neri <ricardo.neri@intel.com>,
	Stephane Eranian <eranian@google.com>,
	Ingo Molnar <mingo@kernel.org>,
	Wincy Van <fanwenyi0529@gmail.com>,
	Ashok Raj <ashok.raj@intel.com>,
	x86@kernel.org, Andi Kleen <andi.kleen@intel.com>,
	Borislav Petkov <bp@suse.de>,
	"Eric W. Biederman" <ebiederm@xmission.com>,
	"Ravi V. Shankar" <ravi.v.shankar@intel.com>,
	Bjorn Helgaas <bhelgaas@google.com>,
	Juergen Gross <jgross@suse.com>, Tony Luck <tony.luck@intel.com>,
	Randy Dunlap <rdunlap@infradead.org>,
	linux-kernel@vger.kernel.org, iommu@lists.linux-foundation.org,
	Jacob Pan <jacob.jun.pan@intel.com>,
	Philippe Ombredanne <pombredanne@nexb.com>
Subject: Re: [RFC PATCH v4 20/21] iommu/vt-d: hpet: Reserve an interrupt remampping table entry for watchdog
Date: Sun, 16 Jun 2019 21:21:46 +0200 (CEST)
Message-ID: <alpine.DEB.2.21.1906162049300.1760@nanos.tec.linutronix.de> (raw)
In-Reply-To: <1558660583-28561-21-git-send-email-ricardo.neri-calderon@linux.intel.com>

On Thu, 23 May 2019, Ricardo Neri wrote:
> When the hardlockup detector is enabled, the function
> hld_hpet_intremapactivate_irq() activates the recently created entry
> in the interrupt remapping table via the modify_irte() functions. While
> doing this, it specifies which CPU the interrupt must target via its APIC
> ID. This function can be called every time the destination iD of the
> interrupt needs to be updated; there is no need to allocate or remove
> entries in the interrupt remapping table.

Brilliant.

> +int hld_hpet_intremap_activate_irq(struct hpet_hld_data *hdata)
> +{
> +	u32 destid = apic->calc_dest_apicid(hdata->handling_cpu);
> +	struct intel_ir_data *data;
> +
> +	data = (struct intel_ir_data *)hdata->intremap_data;
> +	data->irte_entry.dest_id = IRTE_DEST(destid);
> +	return modify_irte(&data->irq_2_iommu, &data->irte_entry);

This calls modify_irte() which does at the very beginning:

   raw_spin_lock_irqsave(&irq_2_ir_lock, flags);

How is that supposed to work from NMI context? Not to talk about the
other spinlocks which are taken in the subsequent call chain.

You cannot call in any of that code from NMI context.

The only reason why this never deadlocked in your testing is that nothing
else touched that particular iommu where the HPET hangs off concurrently.

But that's just pure luck and not design. 

Thanks,

	tglx
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  parent reply index

Thread overview: 54+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-05-24  1:16 [RFC PATCH v4 00/21] Implement an HPET-based hardlockup detector Ricardo Neri
2019-05-24  1:16 ` [RFC PATCH v4 01/21] x86/msi: Add definition for NMI delivery mode Ricardo Neri
2019-05-24  1:16 ` [RFC PATCH v4 02/21] x86/hpet: Expose hpet_writel() in header Ricardo Neri
2019-05-24  1:16 ` [RFC PATCH v4 03/21] x86/hpet: Calculate ticks-per-second in a separate function Ricardo Neri
2019-06-14 15:54   ` Thomas Gleixner
2019-06-14 15:59     ` Thomas Gleixner
2019-06-18 22:48     ` Ricardo Neri
2019-06-18 23:13       ` Thomas Gleixner
2019-05-24  1:16 ` [RFC PATCH v4 04/21] x86/hpet: Add hpet_set_comparator() for periodic and one-shot modes Ricardo Neri
2019-06-14 18:17   ` Thomas Gleixner
2019-06-18 22:48     ` Ricardo Neri
2019-05-24  1:16 ` [RFC PATCH v4 05/21] x86/hpet: Reserve timer for the HPET hardlockup detector Ricardo Neri
2019-06-11 19:54   ` Thomas Gleixner
2019-06-14  1:14     ` Ricardo Neri
2019-06-14 16:10       ` Thomas Gleixner
2019-06-18 22:48         ` Ricardo Neri
2019-05-24  1:16 ` [RFC PATCH v4 06/21] x86/hpet: Configure the timer used by the " Ricardo Neri
2019-05-24  1:16 ` [RFC PATCH v4 07/21] watchdog/hardlockup: Define a generic function to detect hardlockups Ricardo Neri
2019-05-24  1:16 ` [RFC PATCH v4 08/21] watchdog/hardlockup: Decouple the hardlockup detector from perf Ricardo Neri
2019-05-24  1:16 ` [RFC PATCH v4 09/21] x86/nmi: Add a NMI_WATCHDOG NMI handler category Ricardo Neri
2019-05-24  1:16 ` [RFC PATCH v4 10/21] watchdog/hardlockup: Add function to enable NMI watchdog on all allowed CPUs at once Ricardo Neri
2019-05-24  1:16 ` [RFC PATCH v4 11/21] x86/watchdog/hardlockup: Add an HPET-based hardlockup detector Ricardo Neri
2019-05-24  1:16 ` [RFC PATCH v4 12/21] watchdog/hardlockup/hpet: Adjust timer expiration on the number of monitored CPUs Ricardo Neri
2019-06-11 20:11   ` Thomas Gleixner
2019-06-18 22:46     ` Ricardo Neri
2019-05-24  1:16 ` [RFC PATCH v4 13/21] x86/watchdog/hardlockup/hpet: Determine if HPET timer caused NMI Ricardo Neri
2019-05-24  1:16 ` [RFC PATCH v4 14/21] watchdog/hardlockup: Use parse_option_str() to handle "nmi_watchdog" Ricardo Neri
2019-05-24  1:16 ` [RFC PATCH v4 15/21] watchdog/hardlockup/hpet: Only enable the HPET watchdog via a boot parameter Ricardo Neri
2019-05-24  1:16 ` [RFC PATCH v4 16/21] x86/watchdog: Add a shim hardlockup detector Ricardo Neri
2019-05-24  1:16 ` [RFC PATCH v4 17/21] x86/tsc: Switch to perf-based hardlockup detector if TSC become unstable Ricardo Neri
2019-06-07  0:35   ` Stephane Eranian via iommu
2019-06-07 14:14     ` Ricardo Neri
2019-05-24  1:16 ` [RFC PATCH v4 18/21] x86/apic: Add a parameter for the APIC delivery mode Ricardo Neri
2019-06-16  9:55   ` Thomas Gleixner
2019-06-18 22:47     ` Ricardo Neri
2019-06-18 23:15       ` Thomas Gleixner
2019-05-24  1:16 ` [RFC PATCH v4 19/21] iommu/vt-d: Rework prepare_irte() to support per-irq " Ricardo Neri
2019-05-24  1:16 ` [RFC PATCH v4 20/21] iommu/vt-d: hpet: Reserve an interrupt remampping table entry for watchdog Ricardo Neri
2019-06-16 18:42   ` Thomas Gleixner
2019-06-16 19:21   ` Thomas Gleixner [this message]
2019-06-17  8:25     ` Thomas Gleixner
2019-06-17 21:38       ` Stephane Eranian via iommu
2019-06-17 23:08         ` Thomas Gleixner
2019-06-19 15:43           ` Jacob Pan
2019-06-21 15:33             ` Thomas Gleixner
2019-06-21 17:31               ` Jacob Pan
2019-06-21 18:39                 ` Jacob Pan
2019-06-21 20:05                   ` Thomas Gleixner
2019-06-21 23:55                     ` Ricardo Neri
2019-06-22  7:21                       ` Thomas Gleixner
2019-06-18 22:45       ` Ricardo Neri
2019-05-24  1:16 ` [RFC PATCH v4 21/21] x86/watchdog/hardlockup/hpet: Support interrupt remapping Ricardo Neri
2019-06-16  8:44   ` Thomas Gleixner
2019-06-16  8:53     ` Thomas Gleixner

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