[PATCH v5 09/10] powerpc: snapshot thread flags

[Mark Rutland]

Some thread flags can be set remotely, and so even when IRQs are
disabled, the flags can change under our feet. Generally this is
unlikely to cause a problem in practice, but it is somewhat unsound, and
KCSAN will legitimately warn that there is a data race.

To avoid such issues, a snapshot of the flags has to be taken prior to
using them. Some places already use READ_ONCE() for that, others do not.

Convert them all to the new flag accessor helpers.

Signed-off-by: Mark Rutland <mark.rutland@xxxxxxx>
Acked-by: Paul E. McKenney <paulmck@xxxxxxxxxx>
Cc: Benjamin Herrenschmidt <benh@xxxxxxxxxxxxxxxxxxx>
Cc: Michael Ellerman <mpe@xxxxxxxxxxxxxx>
Cc: Paul Mackerras <paulus@xxxxxxxxx>
---
 arch/powerpc/kernel/interrupt.c     | 13 ++++++-------
 arch/powerpc/kernel/ptrace/ptrace.c |  3 +--
 2 files changed, 7 insertions(+), 9 deletions(-)

diff --git a/arch/powerpc/kernel/interrupt.c b/arch/powerpc/kernel/interrupt.c
index a73f3f70a657..073762601a7e 100644
--- a/arch/powerpc/kernel/interrupt.c
+++ b/arch/powerpc/kernel/interrupt.c
@@ -138,7 +138,7 @@ notrace long system_call_exception(long r3, long r4, long r5,
 
 	local_irq_enable();
 
-	if (unlikely(current_thread_info()->flags & _TIF_SYSCALL_DOTRACE)) {
+	if (unlikely(read_thread_flags() & _TIF_SYSCALL_DOTRACE)) {
 		if (unlikely(trap_is_unsupported_scv(regs))) {
 			/* Unsupported scv vector */
 			_exception(SIGILL, regs, ILL_ILLOPC, regs->nip);
@@ -300,7 +300,7 @@ interrupt_exit_user_prepare_main(unsigned long ret, struct pt_regs *regs)
 	unsigned long ti_flags;
 
 again:
-	ti_flags = READ_ONCE(current_thread_info()->flags);
+	ti_flags = read_thread_flags();
 	while (unlikely(ti_flags & (_TIF_USER_WORK_MASK & ~_TIF_RESTORE_TM))) {
 		local_irq_enable();
 		if (ti_flags & _TIF_NEED_RESCHED) {
@@ -316,7 +316,7 @@ interrupt_exit_user_prepare_main(unsigned long ret, struct pt_regs *regs)
 			do_notify_resume(regs, ti_flags);
 		}
 		local_irq_disable();
-		ti_flags = READ_ONCE(current_thread_info()->flags);
+		ti_flags = read_thread_flags();
 	}
 
 	if (IS_ENABLED(CONFIG_PPC_BOOK3S_64) && IS_ENABLED(CONFIG_PPC_FPU)) {
@@ -394,7 +394,7 @@ notrace unsigned long syscall_exit_prepare(unsigned long r3,
 	/* Check whether the syscall is issued inside a restartable sequence */
 	rseq_syscall(regs);
 
-	ti_flags = current_thread_info()->flags;
+	ti_flags = read_thread_flags();
 
 	if (unlikely(r3 >= (unsigned long)-MAX_ERRNO) && is_not_scv) {
 		if (likely(!(ti_flags & (_TIF_NOERROR | _TIF_RESTOREALL)))) {
@@ -489,8 +489,7 @@ notrace unsigned long interrupt_exit_kernel_prepare(struct pt_regs *regs)
 	unsigned long flags;
 	unsigned long ret = 0;
 	unsigned long kuap;
-	bool stack_store = current_thread_info()->flags &
-						_TIF_EMULATE_STACK_STORE;
+	bool stack_store = read_thread_flags() & _TIF_EMULATE_STACK_STORE;
 
 	if (regs_is_unrecoverable(regs))
 		unrecoverable_exception(regs);
@@ -511,7 +510,7 @@ notrace unsigned long interrupt_exit_kernel_prepare(struct pt_regs *regs)
 again:
 		if (IS_ENABLED(CONFIG_PREEMPT)) {
 			/* Return to preemptible kernel context */
-			if (unlikely(current_thread_info()->flags & _TIF_NEED_RESCHED)) {
+			if (unlikely(read_thread_flags() & _TIF_NEED_RESCHED)) {
 				if (preempt_count() == 0)
 					preempt_schedule_irq();
 			}
diff --git a/arch/powerpc/kernel/ptrace/ptrace.c b/arch/powerpc/kernel/ptrace/ptrace.c
index 7c7093c17c45..c43f77e2ac31 100644
--- a/arch/powerpc/kernel/ptrace/ptrace.c
+++ b/arch/powerpc/kernel/ptrace/ptrace.c
@@ -260,8 +260,7 @@ long do_syscall_trace_enter(struct pt_regs *regs)
 {
 	u32 flags;
 
-	flags = READ_ONCE(current_thread_info()->flags) &
-		(_TIF_SYSCALL_EMU | _TIF_SYSCALL_TRACE);
+	flags = read_thread_flags() & (_TIF_SYSCALL_EMU | _TIF_SYSCALL_TRACE);
 
 	if (flags) {
 		int rc = tracehook_report_syscall_entry(regs);
-- 
2.11.0