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Date: Tue, 4 Dec 2018 19:10:40 +0900
From: Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com>
To: Feng Tang <feng.tang@intel.com>
Cc: bp@suse.de, feng.tang@intel.com, keescook@chromium.org,
        mm-commits@vger.kernel.org, pmladek@suse.com,
        sergey.senozhatsky@gmail.com, stable@vger.kernel.org,
        tglx@linutronix.de, akpm@linux-foundation.org,
        peterz@infradead.org, rostedt@goodmis.org
Subject: Re: + panic-avoid-the-extra-noise-dmesg.patch added to -mm tree
Message-ID: <20181204100745.GA530@jagdpanzerIV>
References: <20181204071531.z62N9NwXC%akpm@linux-foundation.org>
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On (12/03/18 23:15), akpm@linux-foundation.org wrote:
[..]
> Feng Tang wrote:
>
[..]
> 
> For people working in console mode, the screen will first show the panic
> call stack, but immediately overridded by these noisy extra messages, which
> makes debugging much more difficult, as the original context gets lost on
> screen.
> 
> Also these noisy messages will confuse some users, as I have seen many bug
> reporters posted the noisy message into bugzilla, instead of the real panic
> call stack and context.
> 
> Removing the "local_irq_enable" will avoid the noisy message.
> 
> The justification for the removing is: when code runs to this point, it
> means user has chosed to not reboot, or do any special handling by using
> the panic notifier method, no much point in re-enabling the interrupt.

[..]


> @@ -322,7 +322,6 @@ void panic(const char *fmt, ...)
>  	}
>  #endif
>  	pr_emerg("---[ end Kernel panic - not syncing: %s ]---\n", buf);
> -	local_irq_enable();
>  	for (i = 0; ; i += PANIC_TIMER_STEP) {
>  		touch_softlockup_watchdog();
>  		if (i >= i_next) {

Hmm, looking at 2.4 kernel:

---  panic() ---
...
        sti();
        for(;;) {
#if defined(CONFIG_X86) && defined(CONFIG_VT)
                extern void panic_blink(void);
                panic_blink();
#endif
                CHECK_EMERGENCY_SYNC
        }
----------------

CHECK_EMERGENCY_SYNC is

#define CHECK_EMERGENCY_SYNC                    \
        if (emergency_sync_scheduled)           \
                do_emergency_sync();

And emergency_sync_scheduled is set by sysrq.


I wonder if this is still the case - sysrq over serial, for instance,
we want local irqs for that.

	-ss