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Date: Mon, 06 Jun 2011 19:04:31 +0200
From: Peter Zijlstra <peterz@...radead.org>
To: Ingo Molnar <mingo@...e.hu>
Cc: Arne Jansen <lists@...-jansens.de>,
Linus Torvalds <torvalds@...ux-foundation.org>,
mingo@...hat.com, hpa@...or.com, linux-kernel@...r.kernel.org,
efault@....de, npiggin@...nel.dk, akpm@...ux-foundation.org,
frank.rowand@...sony.com, tglx@...utronix.de,
linux-tip-commits@...r.kernel.org
Subject: Re: [debug patch] printk: Add a printk killswitch to robustify NMI
watchdog messages
On Mon, 2011-06-06 at 18:44 +0200, Peter Zijlstra wrote:
>
> @@ -942,25 +953,13 @@ asmlinkage int vprintk(const char *fmt, va_list args)
> if (*p == '\n')
> new_text_line = 1;
> }
> + spin_unlock(&logbuf_lock);
>
> - /*
> - * Try to acquire and then immediately release the
> - * console semaphore. The release will do all the
> - * actual magic (print out buffers, wake up klogd,
> - * etc).
> - *
> - * The console_trylock_for_printk() function
> - * will release 'logbuf_lock' regardless of whether it
> - * actually gets the semaphore or not.
> - */
> - if (console_trylock_for_printk(this_cpu))
> - console_unlock();
FWIW the existing printk recursion logic is broken, console_unlock()
clears printk_cpu but console_trylock_for_printk() can release
logbuf_lock and fail the trylock of console_sem, in which case a
subsequent printk() is perfectly valid and non-recursing.
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