Linux-libre 4.4.1-gnupck-4.4.1-gnu

1 files changed, 18 insertions, 0 deletions

diff --git a/arch/powerpc/kernel/process.c b/arch/powerpc/kernel/process.c
index 646bf4d22..ef2ad2d68 100644
--- a/arch/powerpc/kernel/process.c
+++ b/arch/powerpc/kernel/process.c
@@ -569,6 +569,24 @@ static void tm_reclaim_thread(struct thread_struct *thr,
 	if (!MSR_TM_SUSPENDED(mfmsr()))
 		return;
 
+	/*
+	 * Use the current MSR TM suspended bit to track if we have
+	 * checkpointed state outstanding.
+	 * On signal delivery, we'd normally reclaim the checkpointed
+	 * state to obtain stack pointer (see:get_tm_stackpointer()).
+	 * This will then directly return to userspace without going
+	 * through __switch_to(). However, if the stack frame is bad,
+	 * we need to exit this thread which calls __switch_to() which
+	 * will again attempt to reclaim the already saved tm state.
+	 * Hence we need to check that we've not already reclaimed
+	 * this state.
+	 * We do this using the current MSR, rather tracking it in
+	 * some specific thread_struct bit, as it has the additional
+	 * benifit of checking for a potential TM bad thing exception.
+	 */
+	if (!MSR_TM_SUSPENDED(mfmsr()))
+		return;
+
 	tm_reclaim(thr, thr->regs->msr, cause);
 
 	/* Having done the reclaim, we now have the checkpointed