Validate we call might_sleep() with TASK_RUNNING, which catches places
where we nest blocking primitives, eg. mutex usage in a wait loop.
Since all blocking is arranged through task_struct::state, nesting
this is going to cause two distinct issues:
- the inner primitive will set TASK_RUNNING and the outer will not
block
- the outer sets !TASK_RUNNING and the inner expects to be called
with TASK_RUNNING and blocks forever (mutex_lock).
Signed-off-by: Peter Zijlstra <pet...@infradead.org>
---
include/linux/sched.h | 46 ++++++++++++++++++++++++++++++++++++++++++++--
kernel/sched/core.c | 13 +++++++++++++
2 files changed, 57 insertions(+), 2 deletions(-)
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -241,6 +241,43 @@ extern char ___assert_task_state[1 - 2*!
((task->state & TASK_UNINTERRUPTIBLE) != 0 && \
(task->flags & PF_FROZEN) == 0)
+#ifdef CONFIG_DEBUG_ATOMIC_SLEEP
+
+#define __set_task_state(tsk, state_value) \
+ do { \
+ (tsk)->task_state_change = _THIS_IP_; \
+ (tsk)->state = (state_value); \
+ } while (0)
+#define set_task_state(tsk, state_value) \
+ do { \
+ (tsk)->task_state_change = _THIS_IP_; \
+ set_mb((tsk)->state, (state_value)); \
+ } while (0)
+
+/*
+ * set_current_state() includes a barrier so that the write of current->state
+ * is correctly serialised wrt the caller's subsequent test of whether to
+ * actually sleep:
+ *
+ * set_current_state(TASK_UNINTERRUPTIBLE);
+ * if (do_i_need_to_sleep())
+ * schedule();
+ *
+ * If the caller does not need such serialisation then use
__set_current_state()
+ */
+#define __set_current_state(state_value) \
+ do { \
+ current->task_state_change = _THIS_IP_; \
+ current->state = (state_value); \
+ } while (0)
+#define set_current_state(state_value) \
+ do { \
+ current->task_state_change = _THIS_IP_; \
+ set_mb(current->state, (state_value)); \
+ } while (0)
+
+#else
+
#define __set_task_state(tsk, state_value) \
do { (tsk)->state = (state_value); } while (0)
#define set_task_state(tsk, state_value) \
@@ -257,11 +294,13 @@ extern char ___assert_task_state[1 - 2*!
*
* If the caller does not need such serialisation then use
__set_current_state()
*/
-#define __set_current_state(state_value) \
+#define __set_current_state(state_value) \
do { current->state = (state_value); } while (0)
-#define set_current_state(state_value) \
+#define set_current_state(state_value) \
set_mb(current->state, (state_value))
+#endif
+
/* Task command name length */
#define TASK_COMM_LEN 16
@@ -1650,6 +1689,9 @@ struct task_struct {
unsigned int sequential_io;
unsigned int sequential_io_avg;
#endif
+#ifdef CONFIG_DEBUG_ATOMIC_SLEEP
+ unsigned long task_state_change;
+#endif
};
/* Future-safe accessor for struct task_struct's cpus_allowed. */
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -7077,6 +7077,19 @@ void __might_sleep(const char *file, int
{
static unsigned long prev_jiffy; /* ratelimiting */
+ /*
+ * Blocking primitives will set (and therefore destroy) current->state,
+ * since we will exit with TASK_RUNNING make sure we enter with it,
+ * otherwise we will destroy state.
+ */
+ if (WARN(current->state != TASK_RUNNING,
+ "do not call blocking ops when !TASK_RUNNING; "
+ "state=%lx set at [<%p>] %pS\n",
+ current->state,
+ (void *)current->task_state_change,
+ (void *)current->task_state_change))
+ __set_current_state(TASK_RUNNING);
+
rcu_sleep_check(); /* WARN_ON_ONCE() by default, no rate limit reqd. */
if ((preempt_count_equals(preempt_offset) && !irqs_disabled() &&
!is_idle_task(current)) ||
--
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