linux-kernel - Re: Intermittent Qemu boot hang/regression traced back to INT 0x80 changes

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Date: Wed, 24 Apr 2024 13:03:54 -0700
From: Dave Hansen <dave.hansen@...el.com>
To: Paul Gortmaker <paulg@...nel.org>, Thomas Gleixner <tglx@...utronix.de>,
 "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
 Dave Hansen <dave.hansen@...ux.intel.com>, Borislav Petkov <bp@...en8.de>
Cc: x86@...nel.org, linux-kernel@...r.kernel.org,
 Richard Purdie <richard.purdie@...uxfoundation.org>
Subject: Re: Intermittent Qemu boot hang/regression traced back to INT 0x80
 changes

On 4/24/24 11:58, Paul Gortmaker wrote:
> pci 0000:00:1d.0: [8086:2934] type 00 class 0x0c0300 conventional PCI endpoint
> pci 0000:00:1d.0: BAR 4 [io  0xc080-0xc09f]
> pci 0000:00:1d.1: [8086:2935] type 00 class 0x0c0300 conventional PCI endpoint
> pci 0000:00:1d.1: BAR 4 [io  0xc0a0-0xc0bf]
> pci 0000:00:1d.2: [8086:2936] type 00 class 0x0c0300 conventional PCI endpoint
> <hang - not always exactly here, but always in this block of PCI printk>

Any chance you can figure out what the virtual CPU is doing while it's
hung?  Maybe run these a couple of times on the qemu monitor?

	info registers
	info irqs
	info lapic

to see if it's taking a bunch of interrupts and whether RIP is still
moving around.  A couple of samples of RIP (matched back to the kernel
code via vmlinux) can go a long way to figuring out why it's hung.

I take it that this is before sysrq is working?  If it isn't too early:

	sendkey alt-sysrq-t

is always handy.

Otherwise, I'm a bit stumped.  This code shouldn't even be called before
userspace starts up.  Heck you don't even have CONFIG_IA32_EMULATION on
in your .config.