linux-kernel - Re: [PATCH][RFC] printk: make pr

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Date:   Thu, 25 Aug 2016 23:33:33 +0200
From:   Petr Mladek <pmladek@...e.com>
To:     Sergey Senozhatsky <sergey.senozhatsky@...il.com>
Cc:     Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>,
        Jan Kara <jack@...e.cz>, Kay Sievers <kay@...y.org>,
        Tejun Heo <tj@...nel.org>, Calvin Owens <calvinowens@...com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH][RFC] printk: make pr_cont buffer per-cpu

On Thu 2016-08-25 23:27:40, Petr Mladek wrote:
> On Wed 2016-08-24 23:27:29, Sergey Senozhatsky wrote:
> > On (08/24/16 10:19), Petr Mladek wrote:
> > > > On (08/23/16 13:47), Petr Mladek wrote:
> > > > [..]
> > > > > >  	if (!(lflags & LOG_NEWLINE)) {
> > > > > > +		if (!this_cpu_read(cont_printing)) {
> > > > > > +			if (system_state == SYSTEM_RUNNING) {
> > > > > > +				this_cpu_write(cont_printing, true);
> > > > > > +				preempt_disable();
> > > > > > +			}
> > > > > > +		}
> > > > > 
> > > > > I am afraid that this is not acceptable. It means that printk() will have
> > > > > an unexpected side effect. The missing "\n" at the end of a printed
> > > > > string would disable preemption. See below for more.
> > > > 
> > > > missing '\n' must WARN about "sched while atomic" eventually, so it
> > > > shouldn't go unnoticed or stay hidden.
> > > 
> > > Well, it will still force people to rebuilt a test kernel because they
> > > forget to use '\n" and the test kernel is unusable.
> > 
> > you are right. misusage of printk() will now force user to go and fix
> > it. the kernel most likely will be rebuilt anyway - there is a missing
> > \n after all.
 
> Of course, it would be great to fix it transparently. But if there must
> be a burden, I would prefer to keep it on the "corner" case users
> rather than to push it on everyday users.

Not to say that a messed log is much less painful than a locked system.

Best Regards,
Petr