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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
This commit is contained in:
Mark Rutland 2021-11-29 13:06:44 +00:00 committed by Thomas Gleixner
parent dca99fb643
commit 6ce895128b
3 changed files with 5 additions and 5 deletions
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2
include/linux/entry-kvm.h
View File

@ -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);
}

4
kernel/entry/common.c
View File

@ -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();

4
kernel/entry/kvm.c
View File

@ -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;