ARM: 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: Russell King <linux@armlinux.org.uk>
Link: https://lore.kernel.org/r/20211129130653.2037928-6-mark.rutland@arm.com

diff --git a/arch/arm/kernel/signal.c b/arch/arm/kernel/signal.c
index a41e27a..c532a60 100644 (file)
--- a/arch/arm/kernel/signal.c
+++ b/arch/arm/kernel/signal.c
@@ -631,7 +631,7 @@ do_work_pending(struct pt_regs *regs, unsigned int thread_flags, int syscall)
                        }
                }
                local_irq_disable();
-               thread_flags = current_thread_info()->flags;
+               thread_flags = read_thread_flags();
        } while (thread_flags & _TIF_WORK_MASK);
        return 0;
 }

diff --git a/arch/arm/mm/alignment.c b/arch/arm/mm/alignment.c
index ea81e89..adbb381 100644 (file)
--- a/arch/arm/mm/alignment.c
+++ b/arch/arm/mm/alignment.c
@@ -990,7 +990,7 @@ do_alignment(unsigned long addr, unsigned int fsr, struct pt_regs *regs)
                 * there is no work pending for this thread.
                 */
                raw_local_irq_disable();
-               if (!(current_thread_info()->flags & _TIF_WORK_MASK))
+               if (!(read_thread_flags() & _TIF_WORK_MASK))
                        set_cr(cr_no_alignment);
        }