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From: Suresh Siddha on 17 May 2010 15:10
Currently send_remote_softirq() API's don't allow single call_single_data
struct(like per cpu call_single_data) to be used with multiple
send_remote_softirq() calls in parallel (as each of the send_remote_softirq()
call reinitializes the call_single_data overwriting the inflight usage.

Add a new init_remote_softirq_csd() which will init the call_single_data.
Second send_remote_softirq() from the same cpu will now wait on the csd_lock()
if the prior send_remote_softirq() is not complete.

Signed-off-by: Suresh Siddha <suresh.b.siddha(a)intel.com>
Cc: David S. Miller <davem(a)davemloft.net>
Cc: Jens Axboe <jens.axboe(a)oracle.com>
---
include/linux/interrupt.h | 8 ++++++--
kernel/softirq.c | 41 +++++++++++++++++++++++++++--------------
2 files changed, 33 insertions(+), 16 deletions(-)

Index: tip/kernel/softirq.c
===================================================================
--- tip.orig/kernel/softirq.c
+++ tip/kernel/softirq.c
@@ -578,24 +578,23 @@ static void remote_softirq_receive(void
local_irq_restore(flags);
}

-static int __try_remote_softirq(struct call_single_data *cp, int cpu, int softirq)
+static int __try_remote_softirq(struct call_single_data *cp, int cpu)
{
if (cpu_online(cpu)) {
- cp->func = remote_softirq_receive;
- cp->info = cp;
- cp->flags = 0;
- cp->priv = softirq;
-
__smp_call_function_single(cpu, cp, 0);
return 0;
}
return 1;
}
#else /* CONFIG_USE_GENERIC_SMP_HELPERS */
-static int __try_remote_softirq(struct call_single_data *cp, int cpu, int softirq)
+static int __try_remote_softirq(struct call_single_data *cp, int cpu)
{
return 1;
}
+static void remote_softirq_receive(void *data)
+{
+ return;
+}
#endif

/**
@@ -611,12 +610,12 @@ static int __try_remote_softirq(struct c
* Interrupts must be disabled.
*/
void __send_remote_softirq(struct call_single_data *cp, int cpu, int this_cpu,
- int softirq, int fallback)
+ int fallback)
{
if (cpu == this_cpu)
- __local_trigger(cp, softirq);
- else if (__try_remote_softirq(cp, cpu, softirq) && fallback)
- __local_trigger(cp, softirq);
+ __local_trigger(cp, cp->priv);
+ else if (__try_remote_softirq(cp, cpu) && fallback)
+ __local_trigger(cp, cp->priv);
}
EXPORT_SYMBOL(__send_remote_softirq);

@@ -629,19 +628,33 @@ EXPORT_SYMBOL(__send_remote_softirq);
* Like __send_remote_softirq except that disabling interrupts and
* computing the current cpu is done for the caller.
*/
-void send_remote_softirq(struct call_single_data *cp, int cpu, int softirq,
- int fallback)
+void send_remote_softirq(struct call_single_data *cp, int cpu, int fallback)
{
unsigned long flags;
int this_cpu;

local_irq_save(flags);
this_cpu = smp_processor_id();
- __send_remote_softirq(cp, cpu, this_cpu, softirq, fallback);
+ __send_remote_softirq(cp, cpu, this_cpu, fallback);
local_irq_restore(flags);
}
EXPORT_SYMBOL(send_remote_softirq);

+/***
+ * init_remote_softirq_csd - initialize the smp_call_function_single()'s
+ * call single data that will be later used by send_remote_softirq()
+ * @cp: private SMP call function data area to be initialized
+ * @softirq: the softirq to be used for the work
+ */
+void init_remote_softirq_csd(struct call_single_data *cp, int softirq)
+{
+ cp->func = remote_softirq_receive;
+ cp->info = cp;
+ cp->flags = 0;
+ cp->priv = softirq;
+}
+EXPORT_SYMBOL(init_remote_softirq_csd);
+
static int __cpuinit remote_softirq_cpu_notify(struct notifier_block *self,
unsigned long action, void *hcpu)
{
Index: tip/include/linux/interrupt.h
===================================================================
--- tip.orig/include/linux/interrupt.h
+++ tip/include/linux/interrupt.h
@@ -420,13 +420,17 @@ DECLARE_PER_CPU(struct list_head [NR_SOF
* work will be queued to the local cpu.
*/
extern void send_remote_softirq(struct call_single_data *cp, int cpu,
- int softirq, int fallback);
+ int fallback);

/* Like send_remote_softirq(), but the caller must disable local cpu interrupts
* and compute the current cpu, passed in as 'this_cpu'.
*/
extern void __send_remote_softirq(struct call_single_data *cp, int cpu,
- int this_cpu, int softirq, int fallback);
+ int this_cpu, int fallback);
+
+/* Initialize the call_single_data to be later used with send_remote_softirq().
+ */
+extern void init_remote_softirq_csd(struct call_single_data *cp, int softirq);

/* Tasklets --- multithreaded analogue of BHs.



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