tjh.dev / kernel
Linux kernel mirror (for testing) git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git
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Merge branch 'locking-urgent-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip

Pull locking fixes from Ingo Molnar:
"Two lockless_dereference() related fixes"

* 'locking-urgent-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
locking/barriers: Suppress sparse warnings in lockless_dereference()
Revert "drm/fb-helper: Reduce READ_ONCE(master) to lockless_dereference"

Linus Torvalds bd3fd451 f28535c1

+4 -4
+1 -1
drivers/gpu/drm/drm_fb_helper.c
··· 464 464 465 465 /* Sometimes user space wants everything disabled, so don't steal the 466 466 * display if there's a master. */ 467 - if (lockless_dereference(dev->master)) 467 + if (READ_ONCE(dev->master)) 468 468 return false; 469 469 470 470 drm_for_each_crtc(crtc, dev) {
+3 -3
include/linux/compiler.h
··· 527 527 * object's lifetime is managed by something other than RCU. That 528 528 * "something other" might be reference counting or simple immortality. 529 529 * 530 - * The seemingly unused void * variable is to validate @p is indeed a pointer 531 - * type. All pointer types silently cast to void *. 530 + * The seemingly unused size_t variable is to validate @p is indeed a pointer 531 + * type by making sure it can be dereferenced. 532 532 */ 533 533 #define lockless_dereference(p) \ 534 534 ({ \ 535 535 typeof(p) _________p1 = READ_ONCE(p); \ 536 - __maybe_unused const void * const _________p2 = _________p1; \ 536 + size_t __maybe_unused __size_of_ptr = sizeof(*(p)); \ 537 537 smp_read_barrier_depends(); /* Dependency order vs. p above. */ \ 538 538 (_________p1); \ 539 539 })