From: Peter Zijlstra <peterz@infradead.org>
To: Christoph Hellwig <hch@infradead.org>
Cc: Andrew Morton <akpm@linux-foundation.org>,
Ingo Molnar <mingo@kernel.org>,
Thomas Gleixner <tglx@linutronix.de>,
Tony Luck <tony.luck@intel.com>, Robert Richter <rric@kernel.org>,
Bjorn Helgaas <bhelgaas@google.com>,
Aaro Koskinen <aaro.koskinen@iki.fi>,
David Daney <david.daney@cavium.com>,
linux-kernel@vger.kernel.org
Subject: Re: smp_call_function_single with wait=0 considered harmful
Date: Fri, 28 Feb 2014 13:26:24 +0100 [thread overview]
Message-ID: <20140228122624.GF9987@twins.programming.kicks-ass.net> (raw)
In-Reply-To: <20131204164627.GA27677@infradead.org>
On Wed, Dec 04, 2013 at 08:46:27AM -0800, Christoph Hellwig wrote:
> While doing my recent work on the generic smp function calls I noticed
> that smp_call_function_single without the wait flag can't work, as
> it allocates struct call_single_data on stack, and without the wait
> flag will happily return before the IPI has been executed.
It doesn't actually; it uses a per-cpu one in the !wait case.
The subsequent csd_lock() ensures it will wait for any prior user to
complete, so only if you're doing multiple smp_call_function_single()
invocations back-to-back will they queue up.
> This affects the following callers:
<snip>
> kernel/stop_machine.c:stop_two_cpus()
That site should work with .wait=1 just fine, but given the above, the
.wait=0 doesn't appear problematic at all.
next prev parent reply other threads:[~2014-02-28 12:26 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2013-12-04 16:46 smp_call_function_single with wait=0 considered harmful Christoph Hellwig
2013-12-05 21:43 ` Bjorn Helgaas
2013-12-06 10:56 ` Christoph Hellwig
2014-02-28 12:26 ` Peter Zijlstra [this message]
2014-02-28 12:39 ` Peter Zijlstra
2014-02-28 17:06 ` Rik van Riel
2014-02-28 17:34 ` Prarit Bhargava
2014-03-11 12:36 ` [tip:sched/core] stop_machine: Fix^2 race between stop_two_cpus() and stop_cpus() tip-bot for Peter Zijlstra
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