[RFC 5/6] powerpc/mm: Rework nohash TLB broadcast locking

["Ritesh Harjani (IBM)" <ritesh.list@gmail.com>]

Clang's context analysis reports:
  mmu_context.c:141:2: error: releasing raw_spinlock 'context_lock' that was not held [-Werror,-Wthread-safety-analysis]
  mmu_context.c:147:1: error: raw_spinlock 'context_lock' is not held on every path through here [-Werror,-Wthread-safety-analysis]

  tlb.c:257:4: error: raw_spinlock 'tlbivax_lock' is not held on every path through here [-Werror,-Wthread-safety-analysis]
  tlb.c:259:5: error: releasing raw_spinlock 'tlbivax_lock' that was not held [-Werror,-Wthread-safety-analysis]

This reworks the locking in __flush_tlb_page() a bit to satisfy clang
context analyzer requirement.
Also steal_context_smp() drops the context_lock, so it needs to be
annotated with __must_hold to inform the clang analyzer that this
function holds the context_lock.

Signed-off-by: Ritesh Harjani (IBM) <ritesh.list@gmail.com>
---
 arch/powerpc/mm/nohash/mmu_context.c | 1 +
 arch/powerpc/mm/nohash/tlb.c         | 8 +++++---
 2 files changed, 6 insertions(+), 3 deletions(-)

diff --git a/arch/powerpc/mm/nohash/mmu_context.c b/arch/powerpc/mm/nohash/mmu_context.c
index 28a96a10c907..bdbe1f55f388 100644
--- a/arch/powerpc/mm/nohash/mmu_context.c
+++ b/arch/powerpc/mm/nohash/mmu_context.c
@@ -95,6 +95,7 @@ static DEFINE_RAW_SPINLOCK(context_lock);
  *  -- benh
  */
 static unsigned int steal_context_smp(unsigned int id)
+			__must_hold(&context_lock)
 {
 	struct mm_struct *mm;
 	unsigned int cpu, max, i;
diff --git a/arch/powerpc/mm/nohash/tlb.c b/arch/powerpc/mm/nohash/tlb.c
index 07a2db16c2b1..9297549aef41 100644
--- a/arch/powerpc/mm/nohash/tlb.c
+++ b/arch/powerpc/mm/nohash/tlb.c
@@ -252,11 +252,13 @@ void __flush_tlb_page(struct mm_struct *mm, unsigned long vmaddr,
 		/* If broadcast tlbivax is supported, use it */
 		if (mmu_has_feature(MMU_FTR_USE_TLBIVAX_BCAST)) {
 			int lock = mmu_has_feature(MMU_FTR_LOCK_BCAST_INVAL);
-			if (lock)
+			if (lock) {
 				raw_spin_lock(&tlbivax_lock);
-			_tlbivax_bcast(vmaddr, pid, tsize, ind);
-			if (lock)
+				_tlbivax_bcast(vmaddr, pid, tsize, ind);
 				raw_spin_unlock(&tlbivax_lock);
+			} else {
+				_tlbivax_bcast(vmaddr, pid, tsize, ind);
+			}
 			goto bail;
 		} else {
 			struct tlb_flush_param p = {
-- 
2.39.5