linux-kernel - Re: [PATCH] panic: lockdep: correct lock debugging state check

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Message-ID: <20160426123955.GT3448@twins.programming.kicks-ass.net>
Date:	Tue, 26 Apr 2016 14:39:55 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Yang Shi <yang.shi@...aro.org>
Cc:	mingo@...hat.com, linux-kernel@...r.kernel.org,
	linaro-kernel@...ts.linaro.org
Subject: Re: [PATCH] panic: lockdep: correct lock debugging state check

On Mon, Apr 25, 2016 at 08:36:37PM -0700, Yang Shi wrote:
> When kernel oops happens, lock debugging is turned off by debug_locks_off()
> in oops_enter() via calling __debug_locks_off() which set debug_locks to 0
> via xchg(). But, calling to __debug_locks_off() to check lock debugging state
> in add_taint() called by oops_end() will always return false since xchg()
> returns the old value of debug_locks which is cleared in oops_enter() already.
> 
> This prevents add_taint() from printing out lock debugging disable information
> although LOCKDEP_NOW_UNRELIABLE is passed to it.
> 
> Check lock debugging state via !debug_locks to fix this. Although
> !__debug_locks_off() could do the same thing, it may look confusing.
> 
What are you smoking? This is the second completely insane patch you
send this week.

This breaks add_taint() and gains us nothing except trivialities. Who
bloody cares about that print if you've just had an OOPS.