Messages in this thread Patch in this message | | | Date | Tue, 29 Sep 2015 03:30:58 -0700 | From | tip-bot for Peter Zijlstra <> | Subject | [tip:sched/core] sched/core: Create preempt_count invariant |
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Commit-ID: e26d555f695ac8a3aa38055dd04bd23c1334723b Gitweb: http://git.kernel.org/tip/e26d555f695ac8a3aa38055dd04bd23c1334723b Author: Peter Zijlstra <peterz@infradead.org> AuthorDate: Tue, 29 Sep 2015 11:28:27 +0200 Committer: Ingo Molnar <mingo@kernel.org> CommitDate: Tue, 29 Sep 2015 12:27:40 +0200
sched/core: Create preempt_count invariant
Ensure that upon scheduling preempt_count == 2; although currently an additional PREEMPT_ACTIVE is still possible.
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Mike Galbraith <efault@gmx.de> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: fweisbec@gmail.com Cc: linux-kernel@vger.kernel.org Cc: oleg@redhat.com Cc: rostedt@goodmis.org Cc: umgwanakikbuti@gmail.com Link: http://lkml.kernel.org/r/20150929093519.817299442@infradead.org Signed-off-by: Ingo Molnar <mingo@kernel.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(-)
diff --git a/arch/x86/include/asm/preempt.h b/arch/x86/include/asm/preempt.h index b12f810..183d95c6 100644 --- a/arch/x86/include/asm/preempt.h +++ b/arch/x86/include/asm/preempt.h @@ -31,7 +31,8 @@ static __always_inline void preempt_count_set(int pc) * 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 { \ diff --git a/include/asm-generic/preempt.h b/include/asm-generic/preempt.h index 0bec580..1d6f104 100644 --- a/include/asm-generic/preempt.h +++ b/include/asm-generic/preempt.h @@ -24,7 +24,7 @@ static __always_inline void preempt_count_set(int pc) * 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 { \ diff --git a/kernel/sched/core.c b/kernel/sched/core.c index a91df61..ecd585c 100644 --- a/kernel/sched/core.c +++ b/kernel/sched/core.c @@ -2588,11 +2588,17 @@ asmlinkage __visible void schedule_tail(struct task_struct *prev) { 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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