linux-kernel - [PATCH 1/1] powerpc: get_wchan(): solve possible race scenario due to parallel wakeup

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Date:	Tue, 19 Apr 2016 15:48:21 +0530
From:	Kautuk Consul <kautuk.consul.1980@...il.com>
To:	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	Paul Mackerras <paulus@...ba.org>,
	Michael Ellerman <mpe@...erman.id.au>,
	Anton Blanchard <anton@...ba.org>,
	Cyril Bur <cyrilbur@...il.com>,
	Michael Neuling <mikey@...ling.org>,
	Anshuman Khandual <khandual@...ux.vnet.ibm.com>
Cc:	linuxppc-dev@...ts.ozlabs.org, linux-kernel@...r.kernel.org,
	Kautuk Consul <kautuk.consul.1980@...il.com>
Subject: [PATCH 1/1] powerpc: get_wchan(): solve possible race scenario due to parallel wakeup

Add a check for p->state == TASK_RUNNING so that any wake-ups on
task_struct p in the interim lead to 0 being returned by get_wchan().

Signed-off-by: Kautuk Consul <kautuk.consul.1980@...il.com>
---
 arch/powerpc/kernel/process.c |    3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/arch/powerpc/kernel/process.c b/arch/powerpc/kernel/process.c
index b8500b4..f233352 100644
--- a/arch/powerpc/kernel/process.c
+++ b/arch/powerpc/kernel/process.c
@@ -1785,7 +1785,8 @@ unsigned long get_wchan(struct task_struct *p)
 
 	do {
 		sp = *(unsigned long *)sp;
-		if (!validate_sp(sp, p, STACK_FRAME_OVERHEAD))
+		if (!validate_sp(sp, p, STACK_FRAME_OVERHEAD) ||
+		    p->state == TASK_RUNNING)
 			return 0;
 		if (count > 0) {
 			ip = ((unsigned long *)sp)[STACK_FRAME_LR_SAVE];
-- 
1.7.9.5