On Thu, 2016-08-18 at 14:02 -0700, Paul E. McKenney wrote: > Hello, Eric, > > Does Johannes's recent change to lockless_dereference() help with > the sparse issue? > > Thanx, Paul >
Hi Paul Yes indeed, this helps. Thanks ! > ----- Forwarded message from Ingo Molnar <[email protected]> ----- > > Date: Thu, 18 Aug 2016 22:34:21 +0200 > From: Ingo Molnar <[email protected]> > To: Linus Torvalds <[email protected]> > Cc: [email protected], Peter Zijlstra <[email protected]>, > Thomas Gleixner <[email protected]>, Andrew Morton > <[email protected]>, "Paul E. McKenney" <[email protected]> > Subject: [GIT PULL] locking fixes > > Linus, > > Please pull the latest locking-urgent-for-linus git tree from: > > git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip.git > locking-urgent-for-linus > > # HEAD: 112dc0c8069e5554e0ad29c58228f1e6ca49e13d locking/barriers: > Suppress sparse warnings in lockless_dereference() > > Two lockless_dereference() related fixes. > > Thanks, > > Ingo > > ------------------> > Johannes Berg (2): > Revert "drm/fb-helper: Reduce READ_ONCE(master) to lockless_dereference" > locking/barriers: Suppress sparse warnings in lockless_dereference() > > > drivers/gpu/drm/drm_fb_helper.c | 2 +- > include/linux/compiler.h | 6 +++--- > 2 files changed, 4 insertions(+), 4 deletions(-) > > diff --git a/drivers/gpu/drm/drm_fb_helper.c b/drivers/gpu/drm/drm_fb_helper.c > index ce54e985d91b..0a06f9120b5a 100644 > --- a/drivers/gpu/drm/drm_fb_helper.c > +++ b/drivers/gpu/drm/drm_fb_helper.c > @@ -464,7 +464,7 @@ static bool drm_fb_helper_is_bound(struct drm_fb_helper > *fb_helper) > > /* Sometimes user space wants everything disabled, so don't steal the > * display if there's a master. */ > - if (lockless_dereference(dev->master)) > + if (READ_ONCE(dev->master)) > return false; > > drm_for_each_crtc(crtc, dev) { > diff --git a/include/linux/compiler.h b/include/linux/compiler.h > index 1bb954842725..436aa4e42221 100644 > --- a/include/linux/compiler.h > +++ b/include/linux/compiler.h > @@ -527,13 +527,13 @@ static __always_inline void __write_once_size(volatile > void *p, void *res, int s > * object's lifetime is managed by something other than RCU. That > * "something other" might be reference counting or simple immortality. > * > - * The seemingly unused void * variable is to validate @p is indeed a pointer > - * type. All pointer types silently cast to void *. > + * The seemingly unused size_t variable is to validate @p is indeed a pointer > + * type by making sure it can be dereferenced. > */ > #define lockless_dereference(p) \ > ({ \ > typeof(p) _________p1 = READ_ONCE(p); \ > - __maybe_unused const void * const _________p2 = _________p1; \ > + size_t __maybe_unused __size_of_ptr = sizeof(*(p)); \ > smp_read_barrier_depends(); /* Dependency order vs. p above. */ \ > (_________p1); \ > }) > > > ----- End forwarded message ----- >
