[PATCH] Warn when smp_call_function() is called with interrupts disabled

From: Keith Owens <kaos@sgi.com>

Almost every architecture has a comment above smp_call_function()

 * You must not call this function with disabled interrupts or from a
 * hardware interrupt handler or from a bottom half handler.

I have not seen any problems with calling smp_call_function() from a bottom
half handler, but calling it with interrupts disabled can definitely
deadlock.  This bug is hard to reproduce and even harder to debug.

CPU A                               CPU B
Disable interrupts
                                    smp_call_function()
                                    Take call_lock
                                    Send IPIs
                                    Wait for all cpus to acknowledge IPI
                                    CPU A has not responded, spin waiting
                                    for cpu A to respond, holding call_lock
smp_call_function()
Spin waiting for call_lock
Deadlock                            Deadlock

Change all smp_call_function() to WARN_ON(irqs_disabled()).  It should be
BUG_ON() but some buggy code like SCSI sg will break with BUG_ON, so just
warn for now.  Change it to BUG_ON after the buggy code has been fixed.

arch/alpha/kernel/smp.c

@@ -820,6 +820,9 @@ smp_call_function_on_cpu (void (*func) (void *info), void *info, int retry,
 	unsigned long timeout;
 	int num_cpus_to_call;
 	
+	/* Can deadlock when called with interrupts disabled */
+	WARN_ON(irqs_disabled());
+
 	data.func = func;
 	data.info = info;
 	data.wait = wait;

arch/i386/kernel/smp.c

@@ -519,6 +519,9 @@ int smp_call_function (void (*func) (void *info), void *info, int nonatomic,
 	if (!cpus)
 		return 0;
 
+	/* Can deadlock when called with interrupts disabled */
+	WARN_ON(irqs_disabled());
+
 	data.func = func;
 	data.info = info;
 	atomic_set(&data.started, 0);

arch/i386/mach-voyager/voyager_smp.c

@@ -1106,6 +1106,9 @@ smp_call_function (void (*func) (void *info), void *info, int retry,
 	if (!mask)
 		return 0;
 
+	/* Can deadlock when called with interrupts disabled */
+	WARN_ON(irqs_disabled());
+
 	data.func = func;
 	data.info = info;
 	data.started = mask;

arch/ia64/kernel/smp.c

@@ -308,6 +308,9 @@ smp_call_function (void (*func) (void *info), void *info, int nonatomic, int wai
 	if (!cpus)
 		return 0;
 
+	/* Can deadlock when called with interrupts disabled */
+	WARN_ON(irqs_disabled());
+
 	data.func = func;
 	data.info = info;
 	atomic_set(&data.started, 0);

arch/mips/kernel/smp.c

@@ -151,6 +151,9 @@ int smp_call_function (void (*func) (void *info), void *info, int retry,
 	if (!cpus)
 		return 0;
 
+	/* Can deadlock when called with interrupts disabled */
+	WARN_ON(irqs_disabled());
+
 	data.func = func;
 	data.info = info;
 	atomic_set(&data.started, 0);

arch/parisc/kernel/smp.c

@@ -328,6 +328,9 @@ smp_call_function (void (*func) (void *info), void *info, int retry, int wait)
 	unsigned long timeout;
 	static spinlock_t lock = SPIN_LOCK_UNLOCKED;
 
+	/* Can deadlock when called with interrupts disabled */
+	WARN_ON(irqs_disabled());
+	
 	data.func = func;
 	data.info = info;
 	data.wait = wait;

arch/ppc/kernel/smp.c

@@ -211,6 +211,8 @@ int smp_call_function(void (*func) (void *info), void *info, int nonatomic,
            bitmask. --RR */
 	if (num_online_cpus() <= 1)
 		return 0;
+	/* Can deadlock when called with interrupts disabled */
+	WARN_ON(irqs_disabled());
 	return __smp_call_function(func, info, wait, MSG_ALL_BUT_SELF);
 }
 

arch/ppc64/kernel/smp.c

@@ -692,6 +692,9 @@ int smp_call_function (void (*func) (void *info), void *info, int nonatomic,
 	int ret = -1, cpus;
 	unsigned long timeout;
 
+	/* Can deadlock when called with interrupts disabled */
+	WARN_ON(irqs_disabled());
+
 	data.func = func;
 	data.info = info;
 	atomic_set(&data.started, 0);

arch/s390/kernel/smp.c

@@ -127,6 +127,9 @@ int smp_call_function (void (*func) (void *info), void *info, int nonatomic,
 	if (cpus <= 0)
 		return 0;
 
+	/* Can deadlock when called with interrupts disabled */
+	WARN_ON(irqs_disabled());
+
 	data.func = func;
 	data.info = info;
 	atomic_set(&data.started, 0);

arch/sh/kernel/smp.c

@@ -181,6 +181,9 @@ int smp_call_function(void (*func)(void *info), void *info, int retry, int wait)
 	if (nr_cpus < 2)
 		return 0;
 
+	/* Can deadlock when called with interrupts disabled */
+	WARN_ON(irqs_disabled());
+
 	spin_lock(&smp_fn_call.lock);
 
 	atomic_set(&smp_fn_call.finished, 0);

arch/sparc64/kernel/smp.c

@@ -598,6 +598,9 @@ int smp_call_function(void (*func)(void *info), void *info,
 	if (!cpus)
 		return 0;
 
+	/* Can deadlock when called with interrupts disabled */
+	WARN_ON(irqs_disabled());
+
 	data.func = func;
 	data.info = info;
 	atomic_set(&data.finished, 0);

arch/um/kernel/smp.c

@@ -266,6 +266,9 @@ int smp_call_function(void (*_func)(void *info), void *_info, int nonatomic,
 	if (!cpus)
 		return 0;
 
+	/* Can deadlock when called with interrupts disabled */
+	WARN_ON(irqs_disabled());
+
 	spin_lock_bh(&call_lock);
 	atomic_set(&scf_started, 0);
 	atomic_set(&scf_finished, 0);

arch/x86_64/kernel/smp.c

@@ -404,6 +404,9 @@ int smp_call_function (void (*func) (void *info), void *info, int nonatomic,
 	if (!cpus)
 		return 0;
 
+	/* Can deadlock when called with interrupts disabled */
+	WARN_ON(irqs_disabled());
+
 	data.func = func;
 	data.info = info;
 	atomic_set(&data.started, 0);