linux-kernel - Re: Lockdep warning with init_espfix

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Message-ID: <543E994F.5030406@zytor.com>
Date:	Wed, 15 Oct 2014 08:57:03 -0700
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Prarit Bhargava <prarit@...hat.com>, linux-kernel@...r.kernel.org
CC:	x86@...nel.org
Subject: Re: Lockdep warning with init_espfix_ap()

On 10/09/2014 08:35 AM, Prarit Bhargava wrote:
> 
> Non-fatal warning seen with latest kernel tree during kernel boot.
> 
>  WARNING: CPU: 64 PID: 0 at kernel/locking/lockdep.c:2744
> lockdep_trace_alloc+0xdd/0xe0()
>  DEBUG_LOCKS_WARN_ON(irqs_disabled_flags(flags))
>  Modules linked in:
> 
>  CPU: 64 PID: 0 Comm: swapper/64 Not tainted 3.17.0+ #10
>  Hardware name: Intel Corporation BRICKLAND/BRICKLAND, BIOS
> BIVTSDP1.86B.0049.R00.1403081207 03/08/2014
>   0000000000000000 d27b9ea0e3821f35 ffff88084edc3ce0 ffffffff8171cbd8
>   ffff88084edc3d28 ffff88084edc3d18 ffffffff8108424d 0000000000000046
>   0000000000000000 00000000000000d0 0000000000000002 0000000000000000
>  Call Trace:
>   [<ffffffff8171cbd8>] dump_stack+0x4d/0x66
>   [<ffffffff8108424d>] warn_slowpath_common+0x7d/0xa0
>   [<ffffffff810842cc>] warn_slowpath_fmt+0x5c/0x80
>   [<ffffffff810e3e2d>] lockdep_trace_alloc+0xdd/0xe0
>   [<ffffffff811c0aaf>] __alloc_pages_nodemask+0x9f/0x4b0
>   [<ffffffff81025365>] ? native_sched_clock+0x35/0xa0
>   [<ffffffff810253d9>] ? sched_clock+0x9/0x10
>   [<ffffffff8120981a>] alloc_page_interleave+0x3a/0x90
>   [<ffffffff8120ae8d>] alloc_pages_current+0x17d/0x1f0
>   [<ffffffff811bab24>] ? __get_free_pages+0x14/0x50
>   [<ffffffff811bab24>] __get_free_pages+0x14/0x50
>   [<ffffffff8102225d>] init_espfix_ap+0x17d/0x320
>   [<ffffffff8105254e>] start_secondary+0x19e/0x350
>  ---[ end trace 2b62d796aa7ae001 ]---
> 
>  Debugging ... but sorta hoping someone else may have already seen it ;)
> 

It is kind of a messy situation, because this code needs to allocate
memory but is run before the secondary CPU is fully up.  As such, it is
a false positive, at least in some ways.

	-hpa


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