linux-kernel - Re: [PATCH v4] lib/spinlock_debug.c: prevent a recursive cycle in the debug code

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Date:	Fri, 29 Jan 2016 15:37:24 +0900
From:	Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>
To:	Peter Hurley <peter@...leysoftware.com>
Cc:	Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>,
	Sergey Senozhatsky <sergey.senozhatsky@...il.com>,
	Byungchul Park <byungchul.park@....com>,
	akpm@...ux-foundation.org, mingo@...nel.org,
	linux-kernel@...r.kernel.org, akinobu.mita@...il.com, jack@...e.cz,
	torvalds@...ux-foundation.org
Subject: Re: [PATCH v4] lib/spinlock_debug.c: prevent a recursive cycle in
 the debug code

On (01/29/16 15:16), Sergey Senozhatsky wrote:
> 
>  http://marc.info/?l=linux-kernel&m=144976121529901
> 

hm... I don't like that patch. ->reset() loop must be done outside
of zap_locks(). we can have a printk() recursion in CPU1, but console
driver lock may be owned by CPU2 in driver's handle_IRQ(), for example.
stealing its lock CPU1 is not really good. in my kernels I do this from
panic() path only, where I know that things are already bad.

panic()->console_panic_mode()->{for_each_console()->reset(), zap_locks()}->console_trelock()->console_unlock().

	-ss