linux-kernel - Re: [PATCH v5] lib/spinlock_debug.c: prevent a recursive cycle in the debug code

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Message-ID: <20160201021317.GB1033@swordfish>
Date:	Mon, 1 Feb 2016 11:13:17 +0900
From:	Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>
To:	Byungchul Park <byungchul.park@....com>
Cc:	Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>,
	akpm@...ux-foundation.org, mingo@...nel.org,
	linux-kernel@...r.kernel.org, akinobu.mita@...il.com, jack@...e.cz,
	peter@...leysoftware.com, torvalds@...ux-foundation.org
Subject: Re: [PATCH v5] lib/spinlock_debug.c: prevent a recursive cycle in
 the debug code

On (02/01/16 10:45), Byungchul Park wrote:
> But avoiding an unnecessary recursive cycle is better than panic(). What I handled
> in this patch is the warning case which causes unnecessary lockup and don't need to
> happen.

Hello,

correct, that was one of the reasons why I proposed to
return back to discussion. it's a bit hard to tell if
we have any chance to survive a "lockup suspected"
spin_dump() recursion; even if we have one, it's a race
spin_unlock on CPUA vs. stack overflow on CPUB. we can
be more certain with ->magic mismatch, for example, but
"lockup suspected" is tricky.

	-ss