linux-kernel - Re: [patch] rt: fix ipi kfree(), introduce IPI

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Message-Id: <1234430564.23438.205.camel@twins>
Date:	Thu, 12 Feb 2009 10:22:44 +0100
From:	Peter Zijlstra <peterz@...radead.org>
To:	Ingo Molnar <mingo@...e.hu>
Cc:	Frederic Weisbecker <fweisbec@...il.com>,
	Thomas Gleixner <tglx@...x.de>,
	LKML <linux-kernel@...r.kernel.org>,
	rt-users <linux-rt-users@...r.kernel.org>,
	Steven Rostedt <rostedt@...dmis.org>,
	Carsten Emde <ce@...g.ch>, Clark Williams <williams@...hat.com>
Subject: Re: [patch] rt: fix ipi kfree(), introduce IPI_SOFTIRQ

On Thu, 2009-02-12 at 09:19 +0100, Ingo Molnar wrote:
> * Ingo Molnar <mingo@...e.hu> wrote:
> 
> > hm, that's a complex one - we do kfree() from IPI context, [...]
> 
> The patch below might do the trick - it offloads this to a softirq.
> Not tested yet.

The simple fix is something like:

---
 kernel/smp.c |    8 ++++++++
 1 files changed, 8 insertions(+), 0 deletions(-)

diff --git a/kernel/smp.c b/kernel/smp.c
index bbedbb7..9b974c1 100644
--- a/kernel/smp.c
+++ b/kernel/smp.c
@@ -252,7 +252,11 @@ int smp_call_function_single(int cpu, void (*func) (void *info), void *info,
 			 * will make sure the callee is done with the
 			 * data before a new caller will use it.
 			 */
+#ifndef CONFIG_PREEMPT_RT
 			data = kmalloc(sizeof(*data), GFP_ATOMIC);
+#else
+			data = NULL;
+#endif
 			if (data)
 				data->flags = CSD_FLAG_ALLOC;
 			else {
@@ -347,7 +351,11 @@ void smp_call_function_many(const struct cpumask *mask,
 		return;
 	}
 
+#ifndef CONFIG_PREEMPT_RT
 	data = kmalloc(sizeof(*data) + cpumask_size(), GFP_ATOMIC);
+#else
+	data = NULL;
+#endif
 	if (unlikely(!data)) {
 		/* Slow path. */
 		for_each_online_cpu(cpu) {

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