powerpc: Snapshot thread flags

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@arm.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Acked-by: Paul E. McKenney <paulmck@kernel.org>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: Michael Ellerman <mpe@ellerman.id.au>
Cc: Paul Mackerras <paulus@samba.org>
Link: https://lore.kernel.org/r/20211129130653.2037928-11-mark.rutland@arm.com

diff --git a/arch/powerpc/kernel/interrupt.c b/arch/powerpc/kernel/interrupt.c
index df048e331cbfe40c11af107aeafb02ea86707e16..563ebfcd16e2407af0dae298a7d29bc8dee3a3cb 100644 (file)
--- a/arch/powerpc/kernel/interrupt.c
+++ b/arch/powerpc/kernel/interrupt.c
@@ -181,7 +181,7 @@ 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);
@@ -343,7 +343,7 @@ 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) {
@@ -359,7 +359,7 @@ again:
                        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)) {
@@ -437,7 +437,7 @@ 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)))) {
@@ -532,8 +532,7 @@ 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);
@@ -554,7 +553,7 @@ 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 7c7093c17c45e2014fc2094746cd76d248097a30..c43f77e2ac310af835627bb978161849a7c6671a 100644 (file)
--- 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);