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Date: Mon, 5 Aug 2013 15:46:10 -0700
From: Andrew Morton <akpm@...ux-foundation.org>
To: "Liu, Chuansheng" <chuansheng.liu@...el.com>
Cc: Lai Jiangshan <eag0628@...il.com>,
"mingo@...nel.org" <mingo@...nel.org>,
"peterz@...radead.org" <peterz@...radead.org>,
"jbeulich@...e.com" <jbeulich@...e.com>,
"paulmck@...ux.vnet.ibm.com" <paulmck@...ux.vnet.ibm.com>,
"mina86@...a86.org" <mina86@...a86.org>,
"srivatsa.bhat@...ux.vnet.ibm.com" <srivatsa.bhat@...ux.vnet.ibm.com>,
"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
"Zhang, Jun" <jun.zhang@...el.com>,
"Wu, Fengguang" <fengguang.wu@...el.com>
Subject: Re: [PATCH V2] smp: Give WARN()ing when calling
smp_call_function_many()/single() in serving irq
On Fri, 1 Mar 2013 03:37:11 +0000 "Liu, Chuansheng" <chuansheng.liu@...el.com> wrote:
>
> > spin_lock_bh(&lockB)
> > *Blocking* heredue to
> > CPUC hold it
> > call
> > smp_call_function_many()
> > send IPI
> > interrupt to CPUA
> >
> > wait_csd()
> >
> > *Blocking* here.
> >
> > So it is still deadlock. but your code does not warn it.
> In your case, even you change spin_lock_bh() to spin_lock(), the deadlock is still there. So no relation with _bh() at all,
> Do not need warning for such deadlock case in smp_call_xxx() or for _bh() case.
>
> > so in_softirq() is better than in_serving_softirq() in in_serving_irq(),
> > and results in_serving_irq() is the same as in_interrupt().
> >
> > so please remove in_serving_irq() and use in_interrupt() instead.
> The original patch is using in_interrupt(). https://lkml.org/lkml/2013/2/6/34
>
(ancient thread)
It's not clear (to me) that all these issues are settled. Can we
please take another look at this?
The patch has been in -mm and linux-next for five months with no
issues. But as far as I know, it hasn't detected any kernel bugs, so
perhaps we just don't need it?
From: Chuansheng Liu <chuansheng.liu@...el.com>
Subject: smp: give WARN()ing when calling smp_call_function_many()/single() in serving irq
Currently the functions smp_call_function_many()/single() will give a
WARN()ing only in the case of irqs_disabled(), but that check is not
enough to guarantee execution of the SMP cross-calls.
In many other cases such as softirq handling/interrupt handling, the two
APIs still can not be called, just as the smp_call_function_many()
comments say:
* You must not call this function with disabled interrupts or from a
* hardware interrupt handler or from a bottom half handler. Preemption
* must be disabled when calling this function.
There is a real case for softirq DEADLOCK case:
CPUA CPUB
spin_lock(&spinlock)
Any irq coming, call the irq handler
irq_exit()
spin_lock_irq(&spinlock)
<== Blocking here due to
CPUB hold it
__do_softirq()
run_timer_softirq()
timer_cb()
call smp_call_function_many()
send IPI interrupt to CPUA
wait_csd()
Then both CPUA and CPUB will be deadlocked here.
So we should give a warning in the nmi, hardirq or softirq context as well.
Moreover, adding one new macro in_serving_irq() which indicates we are
processing nmi, hardirq or sofirq.
Signed-off-by: liu chuansheng <chuansheng.liu@...el.com>
Cc: Ingo Molnar <mingo@...e.hu>
Cc: Peter Zijlstra <a.p.zijlstra@...llo.nl>
Tested-by: Fengguang Wu <fengguang.wu@...el.com>
Cc: Lai Jiangshan <eag0628@...il.com>
Signed-off-by: Andrew Morton <akpm@...ux-foundation.org>
---
include/linux/hardirq.h | 5 +++++
kernel/smp.c | 11 +++++++----
2 files changed, 12 insertions(+), 4 deletions(-)
diff -puN include/linux/hardirq.h~smp-give-warning-when-calling-smp_call_function_many-single-in-serving-irq include/linux/hardirq.h
--- a/include/linux/hardirq.h~smp-give-warning-when-calling-smp_call_function_many-single-in-serving-irq
+++ a/include/linux/hardirq.h
@@ -94,6 +94,11 @@
*/
#define in_nmi() (preempt_count() & NMI_MASK)
+/*
+ * Are we in nmi,irq context, or softirq context?
+ */
+#define in_serving_irq() (in_nmi() || in_irq() || in_serving_softirq())
+
#if defined(CONFIG_PREEMPT_COUNT)
# define PREEMPT_CHECK_OFFSET 1
#else
diff -puN kernel/smp.c~smp-give-warning-when-calling-smp_call_function_many-single-in-serving-irq kernel/smp.c
--- a/kernel/smp.c~smp-give-warning-when-calling-smp_call_function_many-single-in-serving-irq
+++ a/kernel/smp.c
@@ -12,6 +12,7 @@
#include <linux/gfp.h>
#include <linux/smp.h>
#include <linux/cpu.h>
+#include <linux/hardirq.h>
#include "smpboot.h"
@@ -243,8 +244,9 @@ int smp_call_function_single(int cpu, sm
* send smp call function interrupt to this cpu and as such deadlocks
* can't happen.
*/
- WARN_ON_ONCE(cpu_online(this_cpu) && irqs_disabled()
- && !oops_in_progress);
+ WARN_ON_ONCE(cpu_online(this_cpu)
+ && (irqs_disabled() || in_serving_irq())
+ && !oops_in_progress);
if (cpu == this_cpu) {
local_irq_save(flags);
@@ -381,8 +383,9 @@ void smp_call_function_many(const struct
* send smp call function interrupt to this cpu and as such deadlocks
* can't happen.
*/
- WARN_ON_ONCE(cpu_online(this_cpu) && irqs_disabled()
- && !oops_in_progress && !early_boot_irqs_disabled);
+ WARN_ON_ONCE(cpu_online(this_cpu)
+ && (irqs_disabled() || in_serving_irq())
+ && !oops_in_progress && !early_boot_irqs_disabled);
/* Try to fastpath. So, what's a CPU they want? Ignoring this one. */
cpu = cpumask_first_and(mask, cpu_online_mask);
_
--
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