linux-kernel - Re: [PATCH] x86/irq: Cure live lock in irq_force_complete

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Message-ID: <20160311223357.GA2544@intel.com>
Date:	Fri, 11 Mar 2016 14:33:57 -0800
From:	"Luck, Tony" <tony.luck@...el.com>
To:	Thomas Gleixner <tglx@...utronix.de>
Cc:	LKML <linux-kernel@...r.kernel.org>,
	Harry Junior <harryjr@...look.fr>, x86@...nel.org,
	Peter Zijlstra <peterz@...radead.org>,
	Joe Lawrence <joe.lawrence@...atus.com>,
	Borislav Petkov <bp@...en8.de>
Subject: Re: [PATCH] x86/irq: Cure live lock in irq_force_complete_move()

With this patch applied my system survives me doing
several rounds of:

# echo 0 | tee /sys/devices/system/cpu/cpu*/online
# echo 1 | tee /sys/devices/system/cpu/cpu*/online

whereas without the patch the first of those went to

[152455.129604] NMI watchdog: Watchdog detected hard LOCKUP on cpu 96
[152455.136943] Kernel panic - not syncing: Hard LOCKUP

I'm not sure we care to optimize the cpu offline path, but I'll note here
that taking all (but one) cpus offline took 52 seconds (for a hundred
and mumble logical cpus).  Bringing them all back is just 4 seconds.

Tested-by: Tony Luck <tony.luck@...el.com>