From: Drew Moseley <dmoseley@mvista.com>
To: linux-kernel@vger.kernel.org
Subject: Unnecessary warnings in smp_send_stop on i386 arch.
Date: Tue, 16 May 2006 19:43:05 -0700
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Hi,

I noticed a scenario where an i386 kernel would print warning messages
about smp_send_stop() being called with interrupts off. ?This can happen
both from panic() and from machine_restart in arch/i386/kernel/reboot.c
if called from an interrupt handler. ?To reproduce I added a sysrq handler
that simply called panic().

I noticed that the same behavior did not occur on the x86_64 architecture.
In investigating the differences between the architectures, I found the
patch with commit ID e6e7c2a9222016f41613d2389d230b03a36c9f20 during the
2.6.12-rc2 timeframe which addressed this issue for the x86_64 architecture.

I modified the i386/kernel/smp.c file to be functionally equivalent to the
x86_64/kernel/smp.c file to address this issue.

Comments?

Drew


Signed-off-by: Drew Moseley <dmoseley@mvista.com>
Description:
? ? Make arch/i386/kernel/smp.c functionally equivalent to 
arch/x86_64/kernel/smp.c
? ? This allows for the case of calling smp_send_stop when interrupts are 
disabled
? ? in a few isolated cases.

Index: linux-2.6.10/arch/i386/kernel/smp.c
===================================================================
--- linux-2.6.10.orig/arch/i386/kernel/smp.c
+++ linux-2.6.10/arch/i386/kernel/smp.c
@@ -560,30 +560,14 @@ void dump_send_ipi(void)
? * this function sends a 'generic call function' IPI to all other CPUs
? * in the system.
? */
-
-int smp_call_function (void (*func) (void *info), void *info, int nonatomic,
-???????????????????????int wait)
-/*
- * [SUMMARY] Run a function on all other CPUs.
- * <func> The function to run. This must be fast and non-blocking.
- * <info> An arbitrary pointer to pass to the function.
- * <nonatomic> currently unused.
- * <wait> If true, wait (atomically) until function has completed on other 
CPUs.
- * [RETURNS] 0 on success, else a negative status code. Does not return until
- * remote CPUs are nearly ready to execute <<func>> or are or have executed.
- *
- * You must not call this function with disabled interrupts or from a
- * hardware interrupt handler or from a bottom half handler.
- */
+static void __smp_call_function (void (*func) (void *info), void *info,
+???????????????????????????????int nonatomic, int wait)
?{
????????struct call_data_struct data;
????????int cpus = num_online_cpus()-1;
?
????????if (!cpus)
-???????????????return 0;
-
-???????/* Can deadlock when called with interrupts disabled */
-???????WARN_ON(irqs_disabled());
+???????????????return;
?
????????data.func = func;
????????data.info = info;
@@ -592,7 +576,6 @@ int smp_call_function (void (*func) (voi
????????if (wait)
????????????????atomic_set(&data.finished, 0);
?
-???????spin_lock(&call_lock);
????????call_data = &data;
????????mb();
????????
@@ -603,11 +586,32 @@ int smp_call_function (void (*func) (voi
????????while (atomic_read(&data.started) != cpus)
????????????????cpu_relax();
?
-???????if (wait)
-???????????????while (atomic_read(&data.finished) != cpus)
-???????????????????????cpu_relax();
-???????spin_unlock(&call_lock);
+???????if (!wait)
+???????????????return;
+
+???????while (atomic_read(&data.finished) != cpus)
+???????????????cpu_relax();
+}
?
+/*
+ * [SUMMARY] Run a function on all other CPUs.
+ * <func> The function to run. This must be fast and non-blocking.
+ * <info> An arbitrary pointer to pass to the function.
+ * <nonatomic> currently unused.
+ * <wait> If true, wait (atomically) until function has completed on other 
CPUs.
+ * [RETURNS] 0 on success, else a negative status code. Does not return until
+ * remote CPUs are nearly ready to execute <<func>> or are or have executed.
+ *
+ * You must not call this function with disabled interrupts or from a
+ * hardware interrupt handler or from a bottom half handler.
+ * Actually there are a few legal cases, like panic.
+ */
+int smp_call_function (void (*func) (void *info), void *info, int nonatomic,
+???????????????????????int wait)
+{
+???????spin_lock(&call_lock);
+???????__smp_call_function(func,info,nonatomic,wait);
+???????spin_unlock(&call_lock);
????????return 0;
?}
?
@@ -630,7 +634,15 @@ void stop_this_cpu (void * dummy)
?
?void smp_send_stop(void)
?{
-???????smp_call_function(stop_this_cpu, NULL, 1, 0);
+???????int nolock = 0;
+???????/* Don't deadlock on the call lock in panic */
+???????if (!spin_trylock(&call_lock)) {
+???????????????/* ignore locking because we have paniced anyways */
+???????????????nolock = 1;
+???????}
+???????__smp_call_function(stop_this_cpu, NULL, 0, 0);
+???????if (!nolock)
+???????????????spin_unlock(&call_lock);
?
????????local_irq_disable();
????????disable_local_APIC();
-
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