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SubjectRe: Fw: [GIT PULL] locking fixes
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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 <mingo@kernel.org> -----
>
> Date: Thu, 18 Aug 2016 22:34:21 +0200
> From: Ingo Molnar <mingo@kernel.org>
> To: Linus Torvalds <torvalds@linux-foundation.org>
> Cc: linux-kernel@vger.kernel.org, Peter Zijlstra <a.p.zijlstra@chello.nl>,
> Thomas Gleixner <tglx@linutronix.de>, Andrew Morton
> <akpm@linux-foundation.org>, "Paul E. McKenney" <paulmck@us.ibm.com>
> 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 -----
>


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