| Message ID | 1507573730-8083-13-git-send-email-mark.rutland@arm.com |
|---|---|
| State | New |
| Headers | show |
| Series | Preparatory work to kill off ACCESS_ONCE() | expand |
On Mon, Oct 09, 2017 at 07:28:49PM +0100, Mark Rutland wrote: > For several reasons, it is desirable to use {READ,WRITE}_ONCE() in > preference to ACCESS_ONCE(), and new code is expected to use one of the > former. So far, there's been no reason to change most existing uses of > ACCESS_ONCE(), as these aren't currently harmful. > > However, for some features it is necessary to instrument reads and > writes separately, which is not possible with ACCESS_ONCE(). This > distinction is critical to correct operation. > > It's possible to transform the bulk of kernel code using the Coccinelle > script below. However, this doesn't handle comments, leaving references > to ACCESS_ONCE() instances which have been removed. As a preparatory > step, this patch converts the workqueue code and comments to use > {READ,WRITE}_ONCE() consistently. ... > Signed-off-by: Mark Rutland <mark.rutland@arm.com> > Cc: Lai Jiangshan <jiangshanlai@gmail.com> > Cc: Tejun Heo <tj@kernel.org> Acked-by: Tejun Heo <tj@kernel.org> If you want me to route it through the workqueue tree, please let me know. Thanks. -- tejun
On Tue, Oct 10, 2017 at 07:06:29AM -0700, Tejun Heo wrote: > On Mon, Oct 09, 2017 at 07:28:49PM +0100, Mark Rutland wrote: > > For several reasons, it is desirable to use {READ,WRITE}_ONCE() in > > preference to ACCESS_ONCE(), and new code is expected to use one of the > > former. So far, there's been no reason to change most existing uses of > > ACCESS_ONCE(), as these aren't currently harmful. > > > > However, for some features it is necessary to instrument reads and > > writes separately, which is not possible with ACCESS_ONCE(). This > > distinction is critical to correct operation. > > > > It's possible to transform the bulk of kernel code using the Coccinelle > > script below. However, this doesn't handle comments, leaving references > > to ACCESS_ONCE() instances which have been removed. As a preparatory > > step, this patch converts the workqueue code and comments to use > > {READ,WRITE}_ONCE() consistently. > ... > > Signed-off-by: Mark Rutland <mark.rutland@arm.com> > > Cc: Lai Jiangshan <jiangshanlai@gmail.com> > > Cc: Tejun Heo <tj@kernel.org> > > Acked-by: Tejun Heo <tj@kernel.org> Thanks! > If you want me to route it through the workqueue tree, please let me > know. I'm not sure what the plan is for merging just yet, but I will let you know as soon as that's figured out. Thanks, Mark.
diff --git a/kernel/workqueue.c b/kernel/workqueue.c index 64d0edf..39831b2 100644 --- a/kernel/workqueue.c +++ b/kernel/workqueue.c @@ -4647,7 +4647,7 @@ static void rebind_workers(struct worker_pool *pool) * concurrency management. Note that when or whether * @worker clears REBOUND doesn't affect correctness. * - * ACCESS_ONCE() is necessary because @worker->flags may be + * WRITE_ONCE() is necessary because @worker->flags may be * tested without holding any lock in * wq_worker_waking_up(). Without it, NOT_RUNNING test may * fail incorrectly leading to premature concurrency @@ -4656,7 +4656,7 @@ static void rebind_workers(struct worker_pool *pool) WARN_ON_ONCE(!(worker_flags & WORKER_UNBOUND)); worker_flags |= WORKER_REBOUND; worker_flags &= ~WORKER_UNBOUND; - ACCESS_ONCE(worker->flags) = worker_flags; + WRITE_ONCE(worker->flags, worker_flags); } spin_unlock_irq(&pool->lock);
For several reasons, it is desirable to use {READ,WRITE}_ONCE() in preference to ACCESS_ONCE(), and new code is expected to use one of the former. So far, there's been no reason to change most existing uses of ACCESS_ONCE(), as these aren't currently harmful. However, for some features it is necessary to instrument reads and writes separately, which is not possible with ACCESS_ONCE(). This distinction is critical to correct operation. It's possible to transform the bulk of kernel code using the Coccinelle script below. However, this doesn't handle comments, leaving references to ACCESS_ONCE() instances which have been removed. As a preparatory step, this patch converts the workqueue code and comments to use {READ,WRITE}_ONCE() consistently. ---- virtual patch @ depends on patch @ expression E1, E2; @@ - ACCESS_ONCE(E1) = E2 + WRITE_ONCE(E1, E2) @ depends on patch @ expression E; @@ - ACCESS_ONCE(E) + READ_ONCE(E) ---- Signed-off-by: Mark Rutland <mark.rutland@arm.com> Cc: Lai Jiangshan <jiangshanlai@gmail.com> Cc: Tejun Heo <tj@kernel.org> --- kernel/workqueue.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) -- 1.9.1