On Fri, 2013-05-24 at 10:23 -0400, Dave Jones wrote:
> .config: http://paste.fedoraproject.org/14281/94052971/raw/
>
> trace shows the problem process was 'cc1', so I was likely building a kernel
> at the time. There was also a trinity run going on in the background.
>
> cmdline: nothing special..
>
> BOOT_IMAGE=/vmlinuz-3.10.0-rc2+
> root=UUID=bee21cd9-1852-4d1d-9e9d-2e44332b8df1 ro rd.md=0 rd.lvm=0 rd.dm=0
> vconsole.keymap=us rd.luks=0 vconsole.font=latarcyrheb-sun16 consoleblank=0
> console=ttyUSB0,115200 console=tty0 pause_on_oops=30 audit=0
>
OK, I'm able to reproduce this. Looks like the same issue happens from
other ways from userspace into the kernel (the next way was tracing
system calls).
Forget the other patch. Here's a new patch that is more specific to
tracing and context tracking.
Can you try this one out, please.
-- Steve
diff --git a/include/linux/preempt.h b/include/linux/preempt.h
index 87a03c7..f5d4723 100644
--- a/include/linux/preempt.h
+++ b/include/linux/preempt.h
@@ -33,9 +33,25 @@ do { \
preempt_schedule(); \
} while (0)
+#ifdef CONFIG_CONTEXT_TRACKING
+
+void preempt_schedule_context(void);
+
+#define preempt_check_resched_context() \
+do { \
+ if (unlikely(test_thread_flag(TIF_NEED_RESCHED))) \
+ preempt_schedule_context(); \
+} while (0)
+#else
+
+#define preempt_check_resched_context() preempt_check_resched()
+
+#endif /* CONFIG_CONTEXT_TRACKING */
+
#else /* !CONFIG_PREEMPT */
#define preempt_check_resched() do { } while (0)
+#define preempt_check_resched_context() do { } while (0)
#endif /* CONFIG_PREEMPT */
@@ -88,7 +104,7 @@ do { \
do { \
preempt_enable_no_resched_notrace(); \
barrier(); \
- preempt_check_resched(); \
+ preempt_check_resched_context(); \
} while (0)
#else /* !CONFIG_PREEMPT_COUNT */
diff --git a/kernel/context_tracking.c b/kernel/context_tracking.c
index 65349f0..ac3a312 100644
--- a/kernel/context_tracking.c
+++ b/kernel/context_tracking.c
@@ -71,6 +71,46 @@ void user_enter(void)
local_irq_restore(flags);
}
+/**
+ * preempt_schedule_context - preempt_schedule called by tracing
+ *
+ * The tracing infrastructure uses preempt_enable_notrace to prevent
+ * recursion and tracing preempt enabling caused by the tracing
+ * infrastructure itself. But as tracing can happen in areas coming
+ * from userspace or just about to enter userspace, a preempt enable
+ * can occur before user_exit() is called. This will cause the scheduler
+ * to be called when the system is still in usermode.
+ *
+ * To prevent this, the preempt_enable_notrace will use this function
+ * instead of preempt_schedule() to exit user context if needed before
+ * calling the scheduler.
+ */
+void __sched notrace preempt_schedule_context(void)
+{
+ struct thread_info *ti = current_thread_info();
+ enum ctx_state prev_ctx;
+
+ if (likely(ti->preempt_count || irqs_disabled()))
+ return;
+
+ /*
+ * Need to disable preemption in case user_exit() is traced
+ * and the tracer calls preempt_enable_notrace() causing
+ * an infinite recursion.
+ */
+ preempt_disable_notrace();
+ prev_ctx = this_cpu_read(context_tracking.state);
+ user_exit();
+ preempt_enable_no_resched_notrace();
+
+ preempt_schedule();
+
+ preempt_disable_notrace();
+ if (prev_ctx == IN_USER)
+ user_enter();
+ preempt_enable_notrace();
+}
+EXPORT_SYMBOL(preempt_schedule_context);
/**
* user_exit - Inform the context tracking that the CPU is
--
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