linux-kernel - Re: [PATCH 2/2] printk: make sure to print log on console.

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Message-ID: <20180601093738.GC1841@jagdpanzerIV>
Date:   Fri, 1 Jun 2018 18:37:38 +0900
From:   Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>
To:     Petr Mladek <pmladek@...e.com>
Cc:     Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>,
        Maninder Singh <maninder1.s@...sung.com>,
        sergey.senozhatsky@...il.com, rostedt@...dmis.org,
        linux-kernel@...r.kernel.org, a.sahrawat@...sung.com,
        pankaj.m@...sung.com, v.narang@...sung.com
Subject: Re: [PATCH 2/2] printk: make sure to print log on console.

On (06/01/18 11:09), Petr Mladek wrote:
> > [...]
> > 
> > > So I'd say that most likely the following scenarios can suffer:
> > > 
> > > - NMI comes in, sets loglevel to X, printk-s some data, restores the
> > >   loglevel back to Y
> > > - IRQ comes in [like sysrq, etc] comes in and does the same thing
> > > - software exception comes in and does the same thing [e.g. bust_spinlocks()
> > >   at arch/s390/mm/fault.c]
> 
> I forgot to say that it was a great point and analyze.

Thanks :)

> > My view is:
> > 
> > The race with another printk() (console_lock owner) is much more
> > likely than a race between two CPUs manipulating console_loglevel.
> > 
> > The proposed patch seems to be in the right direction. It is supposed
> > to fix the most likely scenario. We could block it and request full
> > solution but I wonder if it is worth it.
> > 
> > I am personally fine with this partial solution for now. We could
> > always make it better if people meet the other scenarios.
> 
> I am still fine with the partial solution. Well, I will think
> more about it before approving any patch.

Same here. I don't mind the patch and can agree with this partial
solution [may be we are missing more cases?]. Probably will need
a little bit more time.

	-ss