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

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Message-ID: <20160131124007.GB1306@swordfish>
Date:	Sun, 31 Jan 2016 21:40:08 +0900
From:	Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>
To:	Byungchul Park <byungchul.park@....com>
Cc:	akpm@...ux-foundation.org, mingo@...nel.org,
	linux-kernel@...r.kernel.org, akinobu.mita@...il.com, jack@...e.cz,
	sergey.senozhatsky.work@...il.com, peter@...leysoftware.com,
	torvalds@...ux-foundation.org
Subject: Re: [PATCH v5] lib/spinlock_debug.c: prevent a recursive cycle in
 the debug code

On (01/29/16 21:54), Byungchul Park wrote:
> Hello, Andrew
> 
> Please take this v5 patch instead of v2 patch, which you took. Or give your
> opinion.
> 
> > It causes an infinite recursive cycle when using CONFIG_DEBUG_SPINLOCK,
> > in the spin_dump(). Backtrace prints printk() -> console_trylock() ->
> > do_raw_spin_lock() -> spin_dump() -> printk()... infinitely.
> > 
> > When the spin_dump() is called from printk(), we should prevent the
> > debug spinlock code from calling printk() again in that context. It's
> > reasonable to avoid printing "lockup suspected" which is just a warning
> > message but it would cause a real lockup definitely.


Hello Byungchul,

thanks for the patch and thanks for bringing this topic to discussion.
let's not rush, if you don't mind, and return back for a bit. there are
some serious cases (when we really would want to see a spin_dump output)
that are broken.

	-ss