Ensure that upon scheduling preempt_count == 2; although currently an
additional PREEMPT_ACTIVE is still possible.
Signed-off-by: Peter Zijlstra (Intel) <pet...@infradead.org>
---
arch/x86/include/asm/preempt.h | 3 ++-
include/asm-generic/preempt.h | 2 +-
kernel/sched/core.c | 14 ++++++++++----
3 files changed, 13 insertions(+), 6 deletions(-)
--- a/arch/x86/include/asm/preempt.h
+++ b/arch/x86/include/asm/preempt.h
@@ -31,7 +31,8 @@ static __always_inline void preempt_coun
* must be macros to avoid header recursion hell
*/
#define init_task_preempt_count(p) do { \
- task_thread_info(p)->saved_preempt_count = PREEMPT_DISABLED; \
+ task_thread_info(p)->saved_preempt_count = \
+ 2*PREEMPT_DISABLE_OFFSET + PREEMPT_NEED_RESCHED; \
} while (0)
#define init_idle_preempt_count(p, cpu) do { \
--- a/include/asm-generic/preempt.h
+++ b/include/asm-generic/preempt.h
@@ -24,7 +24,7 @@ static __always_inline void preempt_coun
* must be macros to avoid header recursion hell
*/
#define init_task_preempt_count(p) do { \
- task_thread_info(p)->preempt_count = PREEMPT_DISABLED; \
+ task_thread_info(p)->preempt_count = 2*PREEMPT_DISABLED; \
} while (0)
#define init_idle_preempt_count(p, cpu) do { \
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -2588,11 +2588,17 @@ asmlinkage __visible void schedule_tail(
{
struct rq *rq;
- /* finish_task_switch() drops rq->lock and enables preemtion */
- preempt_disable();
- rq = finish_task_switch(prev);
+ /*
+ * Still have preempt_count() == 2, from:
+ *
+ * schedule()
+ * preempt_disable(); // 1
+ * __schedule()
+ * raw_spin_lock_irq(&rq->lock) // 2
+ */
+ rq = finish_task_switch(prev); /* drops rq->lock, preempt_count() == 1
*/
balance_callback(rq);
- preempt_enable();
+ preempt_enable(); /* preempt_count() == 0 */
if (current->set_child_tid)
put_user(task_pid_vnr(current), current->set_child_tid);
--
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