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@gmail.com>
[mpe: Confirmed other architectures do similar]
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>

diff --git a/arch/powerpc/kernel/process.c b/arch/powerpc/kernel/process.c
index a0c74bbf345426bc9918860a203b8ab3427a3390..166145b18728b598a0f7091ef495d8fe437cdb72 100644 (file)
--- a/arch/powerpc/kernel/process.c
+++ b/arch/powerpc/kernel/process.c
@@ -1898,7 +1898,8 @@ 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];