linux-kernel - Re: [PATCH] tty_io: fix race in master pty close/slave pty close path

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Message-ID: <45DDDCAB.1000703@zytor.com>
Date:	Thu, 22 Feb 2007 10:10:51 -0800
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Aristeu Sergio Rozanski Filho <aristeu.sergio@...il.com>
CC:	linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] tty_io: fix race in master pty close/slave pty close
 path

Aristeu Sergio Rozanski Filho wrote:
> 
> This normally would only issue a warning on idr_remove() but in case of a
> customer's critical application, it's never too simple:
> 
> thread1: opens master, gets index X
> thread1: begin closing master
> thread2: begin opening slave with index X
> thread1: finishes closing master, index X released
> thread3: opens master, gets index X, just released
> thread2: fails opening slave, releases index X         <----
> thread4: opens master, gets index X, init_dev() then find an already in use
> 	 and healthy tty and fails
> 

OK, that's fiendishly subtle, as most races are, of course.  I'll try to 
walk through the codepaths to make sure the proposed patch doesn't 
introduce a leak, but the concept sounds good.

	-hpa
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