linux-kernel - Re: [PATCH -v2] use per cpu data for single cpu ipi calls

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Date:	Thu, 29 Jan 2009 13:31:28 -0500 (EST)
From:	Steven Rostedt <rostedt@...dmis.org>
To:	Peter Zijlstra <peterz@...radead.org>
cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Rusty Russell <rusty@...tcorp.com.au>, npiggin@...e.de,
	Ingo Molnar <mingo@...e.hu>,
	Thomas Gleixner <tglx@...utronix.de>,
	Arjan van de Ven <arjan@...radead.org>,
	jens.axboe@...cle.com
Subject: Re: [PATCH -v2] use per cpu data for single cpu ipi calls


On Thu, 29 Jan 2009, Peter Zijlstra wrote:

> On Thu, 2009-01-29 at 10:08 -0800, Linus Torvalds wrote:
> 
> > And are you really sure it cannot be called from within interrupts? I'm 
> > finding a lot of callers of smp_call_function_single(), and while I 
> > couldn't find any that look like interrupts, I also couldn't find any 
> > indication that it never happens.
> 
> Calls with wait=1 are deadlockable when done from within irqs or irq
> disabled sections because two cpus could cross ipi each other and stay
> waiting.
> 
> That leaves us with the !wait case, which wasn't safe because that
> kmalloc could fail, and the fallback was wait, which yields the same
> deadlock.
> 
> That leaves us with 6 cases,
> 
> root@...top:/usr/src/linux-2.6# git grep "smp_call_function_single(.*0)"
> arch/blackfin/kernel/kgdb.c:    smp_call_function_single(cpu, kgdb_passive_cpu_callback, NULL, 0);
> arch/ia64/kernel/smpboot.c:     if (smp_call_function_single(master, sync_master, NULL, 0) < 0) {
> arch/ia64/kvm/kvm-ia64.c:               smp_call_function_single(ipi_pcpu, vcpu_kick_intr, vcpu, 0);
> arch/x86/kvm/x86.c:             smp_call_function_single(ipi_pcpu, vcpu_kick_intr, vcpu, 0);
> arch/x86/oprofile/nmi_int.c:            smp_call_function_single(cpu, nmi_cpu_start, NULL, 0);
> arch/x86/pci/amd_bus.c:         smp_call_function_single(cpu, enable_pci_io_ecs, NULL, 0);
> 
> The kgdb one looks to be buggy, as it calls smp_call_function_single()
> from under irqs disabled.
> 
> Such users should use __smp_call_single_function() with a pre-allocated
> csd.
> 
> Didn't check the others.

Regardless of this, I like your change better than my original. We should 
do that anyway.

-- Steve

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