sched: Debug nested sleeps

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 will cause the inner primitive to set TASK_RUNNING and the outer
will thus not block.

Another observed problem is calling a blocking function from
schedule()->sched_submit_work()->blk_schedule_flush_plug() which will
then destroy the task state for the actual __schedule() call that
comes after it.

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: tglx@linutronix.de
Cc: ilya.dryomov@inktank.com
Cc: umgwanakikbuti@gmail.com
Cc: oleg@redhat.com
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Link: http://lkml.kernel.org/r/20140924082242.591637616@infradead.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>

1 files changed, 13 insertions, 0 deletions

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 0456a55fc27f..5b4b96b27cd7 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -7298,6 +7298,19 @@ void __might_sleep(const char *file, int line, int preempt_offset)
 {
         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)) ||