linux-kernel - RE: [PATCH] printk: do not flush the logbuf into console driver in interrupt

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Message-ID: <27240C0AC20F114CBF8149A2696CBE4A0B2479@SHSMSX101.ccr.corp.intel.com>
Date:	Fri, 18 May 2012 00:16:32 +0000
From:	"Liu, Chuansheng" <chuansheng.liu@...el.com>
To:	Peter Zijlstra <peterz@...radead.org>
CC:	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"tglx@...utronix.de" <tglx@...utronix.de>,
	"Yanmin Zhang <yanmin_zhang@...ux.intel.com>
	(yanmin_zhang@...ux.intel.com)" <yanmin_zhang@...ux.intel.com>
Subject: RE: [PATCH] printk: do not flush the logbuf into console driver in
 interrupt

> Uhm no.. I would very much like to get my OOPSes from interrupt context to
> make it out to the console.
(!oops_in_progress) this condition is in the patch, it should cover OOPSes output
to console in interrupt context, I tested this case just now.

> -----Original Message-----
> From: Peter Zijlstra [mailto:peterz@...radead.org]
> Sent: Thursday, May 17, 2012 5:31 PM
> To: Liu, Chuansheng
> Cc: linux-kernel@...r.kernel.org; tglx@...utronix.de; Yanmin Zhang
> <yanmin_zhang@...ux.intel.com> (yanmin_zhang@...ux.intel.com)
> Subject: Re: [PATCH] printk: do not flush the logbuf into console driver in
> interrupt
> 
> On Thu, 2012-05-17 at 07:46 +0000, Liu, Chuansheng wrote:
> > From: liu chuansheng <chuansheng.liu@...el.com>
> > Subject: [PATCH] printk: do not flush the logbuf into console driver
> > in interrupt
> >
> > When irq handle tried to call printk, and it also has the chance to
> > obtain the console sem, then flush the log buf to console driver,but
> > the console driver often give several ms latency or more when much data in
> log buf existed, it will delay the irq handle.
> >
> > The solution is when calling the printk in interrupt, just write the
> > chars into log buf, and expect other threads to flush it into console driver.
> >
> > Signed-off-by: liu chuansheng <chuansheng.liu@...el.com>
> >
> > diff --git a/kernel/printk.c b/kernel/printk.c index b663c2c..99959e1
> > 100644
> > --- a/kernel/printk.c
> > +++ b/kernel/printk.c
> > @@ -804,7 +804,8 @@ static int console_trylock_for_printk(unsigned int
> cpu)
> >                  * the buffer. We need to hold the console semaphore
> >                  * in order to do this test safely.
> >                  */
> > -               if (!can_use_console(cpu)) {
> > +               if (!can_use_console(cpu) ||
> > +                       (in_interrupt() && (!oops_in_progress))) {
> >                         console_locked = 0;
> >                         wake = 1;
> >                         retval = 0;
> 
> Uhm no.. I would very much like to get my OOPSes from interrupt context to
> make it out to the console.
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