linux-kernel - Re: [PATCH][Resend v2] Fix infinite loop in search_binary

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Message-Id: <201107042110.EDI30723.OLFHOtQSMOFFJV@I-love.SAKURA.ne.jp>
Date:	Mon, 4 Jul 2011 21:10:43 +0900
From:	Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>
To:	richard@....at
Cc:	viro@...iv.linux.org.uk, akpm@...ux-foundation.org,
	linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org
Subject: Re: [PATCH][Resend v2] Fix infinite loop in search_binary_handler()

Richard Weinberger wrote:
> Am Montag 04 Juli 2011, 13:51:55 schrieb Tetsuo Handa:
> > Richard Weinberger wrote:
> > > Running a x86_64 kernel without ia32 emulation and a x86 user land
> > > triggers this issue.
> > 
> > Executing /sbin/modprobe for x86_32 on an x86_64 kernel without x86_32
> > support?
> 
> Yep.
> 
> > Anyway, request_module() calls __request_module() but
> > __request_module() stops at MAX_KMOD_CONCURRENT levels of nesting.
> > So, I think "infinite loop" cannot happen.
> 
> Booting a x86_64 UML kernel with x86_32 user land triggers this issue.
> I always wondered why the UML kernel hangs an consumes 100% CPU.

That's strange... Would you show us printk() output like

	printk(KERN_INFO "Calling request_module()\n");
	request_module("binfmt-%04x", *(unsigned short *)(&bprm->buf[2]));
	printk(KERN_INFO "Returned from request_module()\n");

for demonstrating that __request_module() cannot stop at
MAX_KMOD_CONCURRENT levels of nesting?
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