linux-kernel - x86_64: can boxen lose IPIs during IPI storm?

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Message-ID: <1345640356.26849.59.camel@marge.simpson.net>
Date:	Wed, 22 Aug 2012 14:59:16 +0200
From:	Mike Galbraith <efault@....de>
To:	LKML <linux-kernel@...r.kernel.org>
Cc:	Ingo Molnar <mingo@...e.hu>
Subject: x86_64: can boxen lose IPIs during IPI storm?

Greetings,

Not so hypothetical situation: CPUs are having a major SCSI induced IPI
fest, printk via serial port is happening while the storm is raging.
Can it happen that while IRQs are disabled, multiple IPIs arrive, thus
losing one or more?  Seems like that possibility _has_ to be excluded by
hardware for SMP to actually work (and it generally does;) but...

I ask because of a dump I saw, where CPU3 waits for CPU1 forever after
having IPId all CPUs, with all except CPU1 having responded.  CPU1,
seemingly unaware of any such IPI, was then used to trigger that very
dump, ie was not busted/stuck, which looked rather like a lost IPI.

-Mike

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