linux-kernel - Re: [tip:x86/apic] x86, irq: Use cached IOAPIC entry instead of reading from hardware

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Message-ID: <20141128113358.GB30997@pd.tnic>
Date:	Fri, 28 Nov 2014 12:33:58 +0100
From:	Borislav Petkov <bp@...en8.de>
To:	Jiang Liu <jiang.liu@...ux.intel.com>
Cc:	tip-bot for Jiang Liu <tipbot@...or.com>,
	linux-tip-commits@...r.kernel.org, mingo@...nel.org,
	rdunlap@...radead.org, bhelgaas@...gle.com, hpa@...or.com,
	tony.luck@...el.com, rjw@...ysocki.net, grant.likely@...aro.org,
	konrad.wilk@...cle.com, gregkh@...uxfoundation.org,
	tglx@...utronix.de, yinghai@...nel.org, joro@...tes.org,
	linux-kernel@...r.kernel.org, benh@...nel.crashing.org,
	jroedel@...e.de
Subject: Re: [tip:x86/apic] x86, irq: Use cached IOAPIC entry instead of
 reading from hardware

On Fri, Nov 28, 2014 at 10:31:44AM +0800, Jiang Liu wrote:
> 	Thanks for tracking down to this line of change. I have no
> platform to reproduce this bug, so could you please help to revert this
> commit and apply following patch to get some data about IOAPIC entry?

Yep, the cached data differs from what's in the hw reg sometimes:

dmesg | grep -i ioapic
[    0.000000] ACPI: IOAPIC (id[0x02] address[0xfec00000] gsi_base[0])
[    0.000000] IOAPIC[0]: apic_id 2, version 33, address 0xfec00000, GSI 0-23
[    0.429355] ioapic0 pin9, hardware reg a939, cached data 1a939
[    0.506249] ioapic0 pin9, hardware reg 1a939, cached data 1a939
[    0.521547] ACPI: Using IOAPIC for interrupt routing
[    1.313959] ioapic0 pin19, hardware reg a9c1, cached data 1a9c1
[    1.357875] ioapic0 pin12, hardware reg 93c, cached data 93c
[    1.359204] ioapic0 pin1, hardware reg 931, cached data 931
[    1.367423] ioapic0 pin8, hardware reg 938, cached data 938
[    7.560846] ioapic0 pin17, hardware reg a981, cached data 1a981
[    7.866814] ioapic0 pin18, hardware reg a9a1, cached data 1a9a1
[   10.141662] ioapic0 pin16, hardware reg a942, cached data 1a942

This would explain the failure because the ahci ioapic pin19 has that
discrepancy:

[    1.311476] ahci 0000:00:11.0: version 3.0
[    1.313374] ahci 0000:00:11.0: AHCI 0001.0200 32 slots 1 ports 3 Gbps 0x1 impl SATA mode
[    1.313556] ahci 0000:00:11.0: flags: 64bit ncq sntf ilck pm led clo pmp pio slum part ccc 
[    1.313959] ioapic0 pin19, hardware reg a9c1, cached data 1a9c1
[    1.317281] scsi host0: ahci

Btw, that's 32-bit.

Full dmesg attached.

-- 
Regards/Gruss,
    Boris.

Sent from a fat crate under my desk. Formatting is fine.
--

View attachment "dmesg.log" of type "text/plain" (59644 bytes)