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Date: Sun, 31 Jan 2016 21:40:08 +0900
From: Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com>
To: Byungchul Park <byungchul.park@lge.com>
Cc: akpm@linux-foundation.org, mingo@kernel.org, linux-kernel@vger.kernel.org,
        akinobu.mita@gmail.com, jack@suse.cz,
        sergey.senozhatsky.work@gmail.com, peter@hurleysoftware.com,
        torvalds@linux-foundation.org
Subject: Re: [PATCH v5] lib/spinlock_debug.c: prevent a recursive cycle in
 the debug code
Message-ID: <20160131124007.GB1306@swordfish>
References: <1454071417-20685-1-git-send-email-byungchul.park@lge.com>
 <20160129125457.GI31266@X58A-UD3R>
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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