linux-kernel - Re: [tip:locking/core] futex: Fault/error injection capabilities

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Date:	Mon, 20 Jul 2015 10:35:54 -0400
From:	Dave Jones <davej@...emonkey.org.uk>
To:	hpa@...or.com, dbueso@...e.de, darren@...art.com,
	dave@...olabs.net, linux-kernel@...r.kernel.org, mingo@...nel.org,
	peterz@...radead.org, tglx@...utronix.de
Subject: Re: [tip:locking/core] futex: Fault/error injection capabilities

On Mon, Jul 20, 2015 at 03:57:58AM -0700, tip-bot for Davidlohr Bueso wrote:
 > Commit-ID:  ab51fbab39d864f3223e44a2600fd951df261f0b
 > Gitweb:     http://git.kernel.org/tip/ab51fbab39d864f3223e44a2600fd951df261f0b
 > Author:     Davidlohr Bueso <dave@...olabs.net>
 > AuthorDate: Mon, 29 Jun 2015 23:26:02 -0700
 > Committer:  Thomas Gleixner <tglx@...utronix.de>
 > CommitDate: Mon, 20 Jul 2015 11:45:45 +0200
 > 
 > futex: Fault/error injection capabilities
 > 
 > Although futexes are well known for being a royal pita,
 > we really have very little debugging capabilities - except
 > for relying on tglx's eye half the time.
 > 
 > By simply making use of the existing fault-injection machinery,
 > we can improve this situation, allowing generating artificial
 > uaddress faults and deadlock scenarios. Of course, when this is
 > disabled in production systems, the overhead for failure checks
 > is practically zero -- so this is very cheap at the same time.
 > Future work would be nice to now enhance trinity to make use of
 > this.

If you enable any of the fault injection modules, ie, like you demonstrate here:

 > +- /sys/kernel/debug/fail_futex/ignore-private:
 > +
 > +	Format: { 'Y' | 'N' }
 > +	default is 'N', setting it to 'Y' will disable failure injections
 > +	when dealing with private (address space) futexes.
 > +

each pid gets a a make-it-fail file in /proc/self/.  If present, trinity will set this to 1
for child processes.

So it should work today unless I've missed something.

	Dave
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