[Devel] [PATCH rh7 8/8] x86/mm, kasan: Silence KASAN warnings in get_wchan()

[Andrey Ryabinin]

get_wchan() is racy by design, it may access volatile stack
of running task, thus it may access redzone in a stack frame
and cause KASAN to warn about this.

Use READ_ONCE_NOCHECK() to silence these warnings.

Reported-by: Sasha Levin <sasha.levin at oracle.com>
Signed-off-by: Andrey Ryabinin <aryabinin at virtuozzo.com>
Cc: Alexander Potapenko <glider at google.com>
Cc: Andrew Morton <akpm at linux-foundation.org>
Cc: Andrey Konovalov <andreyknvl at google.com>
Cc: Andy Lutomirski <luto at amacapital.net>
Cc: Borislav Petkov <bp at alien8.de>
Cc: Denys Vlasenko <dvlasenk at redhat.com>
Cc: Dmitry Vyukov <dvyukov at google.com>
Cc: Kostya Serebryany <kcc at google.com>
Cc: Linus Torvalds <torvalds at linux-foundation.org>
Cc: Paul E. McKenney <paulmck at linux.vnet.ibm.com>
Cc: Peter Zijlstra <peterz at infradead.org>
Cc: Thomas Gleixner <tglx at linutronix.de>
Cc: Wolfram Gloger <wmglo at dent.med.uni-muenchen.de>
Cc: kasan-dev <kasan-dev at googlegroups.com>
Link: http://lkml.kernel.org/r/1445243838-17763-3-git-send-email-aryabinin@virtuozzo.com
Signed-off-by: Ingo Molnar <mingo at kernel.org>
(cherry picked from commit f7d27c35ddff7c100d7a98db499ac0040149ac05)
Signed-off-by: Andrey Ryabinin <aryabinin at virtuozzo.com>
---
 arch/x86/kernel/process.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/arch/x86/kernel/process.c b/arch/x86/kernel/process.c
index ee3666a..3b1e6b1 100644
--- a/arch/x86/kernel/process.c
+++ b/arch/x86/kernel/process.c
@@ -514,14 +514,14 @@ unsigned long get_wchan(struct task_struct *p)
 	if (sp < bottom || sp > top)
 		return 0;
 
-	fp = READ_ONCE(*(unsigned long *)sp);
+	fp = READ_ONCE_NOCHECK(*(unsigned long *)sp);
 	do {
 		if (fp < bottom || fp > top)
 			return 0;
-		ip = READ_ONCE(*(unsigned long *)(fp + sizeof(unsigned long)));
+		ip = READ_ONCE_NOCHECK(*(unsigned long *)(fp + sizeof(unsigned long)));
 		if (!in_sched_functions(ip))
 			return ip;
-		fp = READ_ONCE(*(unsigned long *)fp);
+		fp = READ_ONCE_NOCHECK(*(unsigned long *)fp);
 	} while (count++ < 16 && p->state != TASK_RUNNING);
 	return 0;
 }
-- 
2.4.10