Unnecessary warnings in smp_send_stop on i386 arch.

[Drew Moseley <dmoseley@mvista.com>]

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();