context_tracking: Restore correct previous context state on exception exit
On exception exit, we restore the previous context tracking state based on
the regs of the interrupted frame. Iff that frame is in user mode as
stated by user_mode() helper, we restore the context tracking user mode.
However there is a tiny chunck of low level arch code after we pass through
user_enter() and until the CPU eventually resumes userspace.
If an exception happens in this tiny area, exception_enter() correctly
exits the context tracking user mode but exception_exit() won't restore
it because of the value returned by user_mode(regs).
As a result we may return to userspace with the wrong context tracking
state.
To fix this, change exception_enter() to return the context tracking state
prior to its call and pass this saved state to exception_exit(). This restores
the real context tracking state of the interrupted frame.
(May be this patch was suggested to me, I don't recall exactly. If so,
sorry for the missing credit).
Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Li Zhong <zhong@linux.vnet.ibm.com>
Cc: Kevin Hilman <khilman@linaro.org>
Cc: Mats Liljegren <mats.liljegren@enea.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Namhyung Kim <namhyung.kim@lge.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
diff --git a/include/linux/context_tracking.h b/include/linux/context_tracking.h
index 5a69273..365f4a6 100644
--- a/include/linux/context_tracking.h
+++ b/include/linux/context_tracking.h
@@ -5,7 +5,6 @@
#include <linux/percpu.h>
#include <asm/ptrace.h>
-#ifdef CONFIG_CONTEXT_TRACKING
struct context_tracking {
/*
* When active is false, probes are unset in order
@@ -14,12 +13,13 @@
* may be further optimized using static keys.
*/
bool active;
- enum {
+ enum ctx_state {
IN_KERNEL = 0,
IN_USER,
} state;
};
+#ifdef CONFIG_CONTEXT_TRACKING
DECLARE_PER_CPU(struct context_tracking, context_tracking);
static inline bool context_tracking_in_user(void)
@@ -35,14 +35,19 @@
extern void user_enter(void);
extern void user_exit(void);
-static inline void exception_enter(struct pt_regs *regs)
+static inline enum ctx_state exception_enter(void)
{
+ enum ctx_state prev_ctx;
+
+ prev_ctx = this_cpu_read(context_tracking.state);
user_exit();
+
+ return prev_ctx;
}
-static inline void exception_exit(struct pt_regs *regs)
+static inline void exception_exit(enum ctx_state prev_ctx)
{
- if (user_mode(regs))
+ if (prev_ctx == IN_USER)
user_enter();
}
@@ -52,8 +57,8 @@
static inline bool context_tracking_in_user(void) { return false; }
static inline void user_enter(void) { }
static inline void user_exit(void) { }
-static inline void exception_enter(struct pt_regs *regs) { }
-static inline void exception_exit(struct pt_regs *regs) { }
+static inline enum ctx_state exception_enter(void) { return 0; }
+static inline void exception_exit(enum ctx_state prev_ctx) { }
static inline void context_tracking_task_switch(struct task_struct *prev,
struct task_struct *next) { }
#endif /* !CONFIG_CONTEXT_TRACKING */