[Xen-devel] [PATCH v2 1/2] sched: add cond_resched_irq()

["Luis R. Rodriguez" <mcgrof@xxxxxxxxxxxxxxxx>]

From: "Luis R. Rodriguez" <mcgrof@xxxxxxxx>

Under special circumstances we may want to force
voluntary preemption even for CONFIG_PREEMPT=n
with interrupts disabled. This adds helpers to
let us do that.

Cc: Borislav Petkov <bp@xxxxxxx>
Cc: David Vrabel <david.vrabel@xxxxxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Cc: Ingo Molnar <mingo@xxxxxxxxxx>
Cc: "H. Peter Anvin" <hpa@xxxxxxxxx>
Cc: x86@xxxxxxxxxx
Cc: Andy Lutomirski <luto@xxxxxxxxxxxxxx>
Cc: Steven Rostedt <rostedt@xxxxxxxxxxx>
Cc: Masami Hiramatsu <masami.hiramatsu.pt@xxxxxxxxxxx>
Cc: Jan Beulich <JBeulich@xxxxxxxx>
Cc: linux-kernel@xxxxxxxxxxxxxxx
Signed-off-by: Luis R. Rodriguez <mcgrof@xxxxxxxx>
---
 include/linux/sched.h |  7 +++++++
 kernel/sched/core.c   | 10 ++++++++++
 2 files changed, 17 insertions(+)

diff --git a/include/linux/sched.h b/include/linux/sched.h
index 5e344bb..92da927 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -2759,6 +2759,13 @@ static inline int signal_pending_state(long state, 
struct task_struct *p)
  */
 extern int _cond_resched(void);
 
+/*
+ * Voluntarily preempting the kernel even for CONFIG_PREEMPT=n kernels
+ * on very special circumstances. This is to be used with interrupts
+ * disabled.
+ */
+extern int cond_resched_irq(void);
+
 #define cond_resched() ({                      \
        __might_sleep(__FILE__, __LINE__, 0);   \
        _cond_resched();                        \
diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 89e7283..573edb1 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -4239,6 +4239,16 @@ int __sched _cond_resched(void)
 }
 EXPORT_SYMBOL(_cond_resched);
 
+int __sched cond_resched_irq(void)
+{
+       if (should_resched()) {
+               preempt_schedule_irq();
+               return 1;
+       }
+       return 0;
+}
+EXPORT_SYMBOL_GPL(cond_resched_irq);
+
 /*
  * __cond_resched_lock() - if a reschedule is pending, drop the given lock,
  * call schedule, and on return reacquire the lock.
-- 
2.1.1


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