context_tracking: Restore previous state in schedule_user

It appears that some SCHEDULE_USER (asm for schedule_user) callers in arch/x86/kernel/entry_64.S are called from RCU kernel context, and schedule_user will return in RCU user context. This causes RCU warnings and possible failures. This is intended to be a minimal fix suitable for 3.18. Reported-and-tested-by: Dave Jones <davej@redhat.com> Cc: Oleg Nesterov <oleg@redhat.com> Cc: Frédéric Weisbecker <fweisbec@gmail.com> Acked-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Signed-off-by: Andy Lutomirski <luto@amacapital.net> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

context_tracking: Restore previous state in schedule_user
It appears that some SCHEDULE_USER (asm for schedule_user) callers in arch/x86/kernel/entry_64.S are called from RCU kernel context, and schedule_user will return in RCU user context. This causes RCU warnings and possible failures. This is intended to be a minimal fix suitable for 3.18. Reported-and-tested-by: Dave Jones <davej@redhat.com> Cc: Oleg Nesterov <oleg@redhat.com> Cc: Frédéric Weisbecker <fweisbec@gmail.com> Acked-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Signed-off-by: Andy Lutomirski <luto@amacapital.net> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Andy Lutomirski · Linus Torvalds · Eric Lee · Eric Lee · Eric Lee · Eric Lee
1 parent ebcd241a63
Showing 1 changed file with 6 additions and 2 deletions Side-by-side Diff
kernel/sched/core.c
@@ -2874,10 +2874,14 @@
 	 * or we have been woken up remotely but the IPI has not yet arrived,
 	 * we haven't yet exited the RCU idle mode. Do it here manually until
 	 * we find a better solution.
+	 *
+	 * NB: There are buggy callers of this function.  Ideally we
+	 * should warn if prev_state != IN_USER, but that will trigger
+	 * too frequently to make sense yet.
 	 */
-	user_exit();
+	enum ctx_state prev_state = exception_enter();
 	schedule();
-	user_enter();
+	exception_exit(prev_state);
 }
 #endif
...	...	@@ -2874,10 +2874,14 @@
2874	2874	* or we have been woken up remotely but the IPI has not yet arrived,
2875	2875	* we haven't yet exited the RCU idle mode. Do it here manually until
2876	2876	* we find a better solution.
	2877	+ *
	2878	+ * NB: There are buggy callers of this function. Ideally we
	2879	+ * should warn if prev_state != IN_USER, but that will trigger
	2880	+ * too frequently to make sense yet.
2877	2881	*/
2878		- user_exit();
	2882	+ enum ctx_state prev_state = exception_enter();
2879	2883	schedule();
2880		- user_enter();
	2884	+ exception_exit(prev_state);
2881	2885	}
2882	2886	#endif
2883	2887