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SubjectRe: [PATCH v2] PCI/MSI: Avoid torn updates to MSI pairs
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Evan,

Evan Green <evgreen@chromium.org> writes:
> On Tue, Jan 28, 2020 at 6:38 AM Thomas Gleixner <tglx@linutronix.de> wrote:
>> The patch is only lightly tested, but so far it survived.
>>
>
> Hi Thomas,
> Thanks for the patch, I gave it a try. I get the following splat, then a hang:
>
> [ 62.238406] CPU0
> [ 62.241135] ----
> [ 62.243863] lock(vector_lock);
> [ 62.247467] lock(vector_lock);
> [ 62.251071]
> [ 62.251071] *** DEADLOCK ***
> [ 62.251071]
> [ 62.257687] May be due to missing lock nesting notation
> [ 62.257687]
> [ 62.265274] 2 locks held by migration/1/17:
> [ 62.269946] #0: 00000000cfa9d8c3 (&irq_desc_lock_class){-.-.}, at:
> irq_migrate_all_off_this_cpu+0x44/0x28f
> [ 62.280846] #1: 000000006885da2d (vector_lock){-.-.}, at:
> msi_set_affinity+0x13c/0x27b
> [ 62.289801]
> [ 62.289801] stack backtrace:
> [ 62.294669] CPU: 1 PID: 17 Comm: migration/1 Not tainted 4.19.96 #2
> [ 62.310713] Call Trace:
> [ 62.313446] dump_stack+0xac/0x11e
> [ 62.317255] __lock_acquire+0x64f/0x19bc
> [ 62.321646] ? find_held_lock+0x3d/0xb8
> [ 62.325936] ? pci_conf1_write+0x4f/0xdf
> [ 62.330320] lock_acquire+0x1b2/0x1fa
> [ 62.334413] ? apic_retrigger_irq+0x31/0x63
> [ 62.339097] _raw_spin_lock_irqsave+0x51/0x7d
> [ 62.343972] ? apic_retrigger_irq+0x31/0x63
> [ 62.348646] apic_retrigger_irq+0x31/0x63
> [ 62.353124] msi_set_affinity+0x25a/0x27b

Bah. I'm sure I looked at that call chain, noticed the double vector
lock and then forgot. Delta patch below.

Thanks,

tglx

8<--------------
--- a/arch/x86/kernel/apic/msi.c
+++ b/arch/x86/kernel/apic/msi.c
@@ -64,6 +64,7 @@ msi_set_affinity(struct irq_data *irqd,
struct irq_cfg old_cfg, *cfg = irqd_cfg(irqd);
struct irq_data *parent = irqd->parent_data;
unsigned int cpu;
+ bool pending;
int ret;

/* Save the current configuration */
@@ -147,9 +148,13 @@ msi_set_affinity(struct irq_data *irqd,
* vector/CPU. Check whether the transition raced with a device
* interrupt and is pending in the local APICs IRR.
*/
- if (lapic_vector_set_in_irr(cfg->vector))
- irq_data_get_irq_chip(irqd)->irq_retrigger(irqd);
+ pending = lapic_vector_set_in_irr(cfg->vector);
+
unlock_vector_lock();
+
+ if (pending)
+ irq_data_get_irq_chip(irqd)->irq_retrigger(irqd);
+
return ret;
}

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