entry: 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>
Link: https://lore.kernel.org/r/20211129130653.2037928-3-mark.rutland@arm.com

diff --git a/include/linux/entry-kvm.h b/include/linux/entry-kvm.h
index 0d7865a..07c878d 100644 (file)
--- a/include/linux/entry-kvm.h
+++ b/include/linux/entry-kvm.h
@@ -75,7 +75,7 @@ static inline void xfer_to_guest_mode_prepare(void)
  */
 static inline bool __xfer_to_guest_mode_work_pending(void)
 {
-       unsigned long ti_work = READ_ONCE(current_thread_info()->flags);
+       unsigned long ti_work = read_thread_flags();
 
        return !!(ti_work & XFER_TO_GUEST_MODE_WORK);
 }

diff --git a/kernel/entry/common.c b/kernel/entry/common.c
index d5a61d5..bad7136 100644 (file)
--- a/kernel/entry/common.c
+++ b/kernel/entry/common.c
@@ -187,7 +187,7 @@ static unsigned long exit_to_user_mode_loop(struct pt_regs *regs,
                /* Check if any of the above work has queued a deferred wakeup */
                tick_nohz_user_enter_prepare();
 
-               ti_work = READ_ONCE(current_thread_info()->flags);
+               ti_work = read_thread_flags();
        }
 
        /* Return the latest work state for arch_exit_to_user_mode() */
@@ -196,7 +196,7 @@ static unsigned long exit_to_user_mode_loop(struct pt_regs *regs,
 
 static void exit_to_user_mode_prepare(struct pt_regs *regs)
 {
-       unsigned long ti_work = READ_ONCE(current_thread_info()->flags);
+       unsigned long ti_work = read_thread_flags();
 
        lockdep_assert_irqs_disabled();
 

diff --git a/kernel/entry/kvm.c b/kernel/entry/kvm.c
index 49972ee..96d476e 100644 (file)
--- a/kernel/entry/kvm.c
+++ b/kernel/entry/kvm.c
@@ -26,7 +26,7 @@ static int xfer_to_guest_mode_work(struct kvm_vcpu *vcpu, unsigned long ti_work)
                if (ret)
                        return ret;
 
-               ti_work = READ_ONCE(current_thread_info()->flags);
+               ti_work = read_thread_flags();
        } while (ti_work & XFER_TO_GUEST_MODE_WORK || need_resched());
        return 0;
 }
@@ -43,7 +43,7 @@ int xfer_to_guest_mode_handle_work(struct kvm_vcpu *vcpu)
         * disabled in the inner loop before going into guest mode. No need
         * to disable interrupts here.
         */
-       ti_work = READ_ONCE(current_thread_info()->flags);
+       ti_work = read_thread_flags();
        if (!(ti_work & XFER_TO_GUEST_MODE_WORK))
                return 0;