From 331b6d8c7afc2e5b900b9dcd850c265e1ba8d8e7 Mon Sep 17 00:00:00 2001 From: Peter Zijlstra Date: Sun, 22 May 2016 12:48:27 +0200 Subject: locking/barriers: Validate lockless_dereference() is used on a pointer type Use the type to validate the argument @p is indeed a pointer type. Signed-off-by: Peter Zijlstra (Intel) Cc: Alexey Dobriyan Cc: Andrew Morton Cc: Linus Torvalds Cc: Paul E. McKenney Cc: Paul McKenney Cc: Peter Zijlstra Cc: Thomas Gleixner Link: http://lkml.kernel.org/r/20160522104827.GP3193@twins.programming.kicks-ass.net Signed-off-by: Ingo Molnar --- include/linux/compiler.h | 4 ++++ 1 file changed, 4 insertions(+) (limited to 'include/linux/compiler.h') diff --git a/include/linux/compiler.h b/include/linux/compiler.h index 793c0829e3a3..06f27fd9d760 100644 --- a/include/linux/compiler.h +++ b/include/linux/compiler.h @@ -545,10 +545,14 @@ static __always_inline void __write_once_size(volatile void *p, void *res, int s * Similar to rcu_dereference(), but for situations where the pointed-to * 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 *. */ #define lockless_dereference(p) \ ({ \ typeof(p) _________p1 = READ_ONCE(p); \ + __maybe_unused const void * const _________p2 = _________p1; \ smp_read_barrier_depends(); /* Dependency order vs. p above. */ \ (_________p1); \ }) -- cgit v1.2.3 From 1f03e8d2919270bd6ef64f39a45ce8df8a9f012a Mon Sep 17 00:00:00 2001 From: Peter Zijlstra Date: Mon, 4 Apr 2016 10:57:12 +0200 Subject: locking/barriers: Replace smp_cond_acquire() with smp_cond_load_acquire() This new form allows using hardware assisted waiting. Some hardware (ARM64 and x86) allow monitoring an address for changes, so by providing a pointer we can use this to replace the cpu_relax() with hardware optimized methods in the future. Requested-by: Will Deacon Suggested-by: Linus Torvalds Signed-off-by: Peter Zijlstra (Intel) Cc: Andrew Morton Cc: Paul E. McKenney Cc: Peter Zijlstra Cc: Thomas Gleixner Signed-off-by: Ingo Molnar --- include/linux/compiler.h | 25 +++++++++++++++++++------ 1 file changed, 19 insertions(+), 6 deletions(-) (limited to 'include/linux/compiler.h') diff --git a/include/linux/compiler.h b/include/linux/compiler.h index 06f27fd9d760..2bcaedc0f032 100644 --- a/include/linux/compiler.h +++ b/include/linux/compiler.h @@ -305,21 +305,34 @@ static __always_inline void __write_once_size(volatile void *p, void *res, int s }) /** - * smp_cond_acquire() - Spin wait for cond with ACQUIRE ordering + * smp_cond_load_acquire() - (Spin) wait for cond with ACQUIRE ordering + * @ptr: pointer to the variable to wait on * @cond: boolean expression to wait for * * Equivalent to using smp_load_acquire() on the condition variable but employs * the control dependency of the wait to reduce the barrier on many platforms. * + * Due to C lacking lambda expressions we load the value of *ptr into a + * pre-named variable @VAL to be used in @cond. + * * The control dependency provides a LOAD->STORE order, the additional RMB * provides LOAD->LOAD order, together they provide LOAD->{LOAD,STORE} order, * aka. ACQUIRE. */ -#define smp_cond_acquire(cond) do { \ - while (!(cond)) \ - cpu_relax(); \ - smp_rmb(); /* ctrl + rmb := acquire */ \ -} while (0) +#ifndef smp_cond_load_acquire +#define smp_cond_load_acquire(ptr, cond_expr) ({ \ + typeof(ptr) __PTR = (ptr); \ + typeof(*ptr) VAL; \ + for (;;) { \ + VAL = READ_ONCE(*__PTR); \ + if (cond_expr) \ + break; \ + cpu_relax(); \ + } \ + smp_rmb(); /* ctrl + rmb := acquire */ \ + VAL; \ +}) +#endif #endif /* __KERNEL__ */ -- cgit v1.2.3 From 33ac279677dcc2441cb93d8cb9cf7a74df62814d Mon Sep 17 00:00:00 2001 From: Peter Zijlstra Date: Tue, 24 May 2016 13:17:12 +0200 Subject: locking/barriers: Introduce smp_acquire__after_ctrl_dep() Introduce smp_acquire__after_ctrl_dep(), this construct is not uncommon, but the lack of this barrier is. Use it to better express smp_rmb() uses in WRITE_ONCE(), the IPC semaphore code and the qspinlock code. Signed-off-by: Peter Zijlstra (Intel) Cc: Andrew Morton Cc: Linus Torvalds Cc: Paul E. McKenney Cc: Peter Zijlstra Cc: Thomas Gleixner Cc: linux-kernel@vger.kernel.org Signed-off-by: Ingo Molnar --- include/linux/compiler.h | 17 ++++++++++++----- 1 file changed, 12 insertions(+), 5 deletions(-) (limited to 'include/linux/compiler.h') diff --git a/include/linux/compiler.h b/include/linux/compiler.h index 2bcaedc0f032..59a7004fc7dd 100644 --- a/include/linux/compiler.h +++ b/include/linux/compiler.h @@ -304,6 +304,17 @@ static __always_inline void __write_once_size(volatile void *p, void *res, int s __u.__val; \ }) +/** + * smp_acquire__after_ctrl_dep() - Provide ACQUIRE ordering after a control dependency + * + * A control dependency provides a LOAD->STORE order, the additional RMB + * provides LOAD->LOAD order, together they provide LOAD->{LOAD,STORE} order, + * aka. (load)-ACQUIRE. + * + * Architectures that do not do load speculation can have this be barrier(). + */ +#define smp_acquire__after_ctrl_dep() smp_rmb() + /** * smp_cond_load_acquire() - (Spin) wait for cond with ACQUIRE ordering * @ptr: pointer to the variable to wait on @@ -314,10 +325,6 @@ static __always_inline void __write_once_size(volatile void *p, void *res, int s * * Due to C lacking lambda expressions we load the value of *ptr into a * pre-named variable @VAL to be used in @cond. - * - * The control dependency provides a LOAD->STORE order, the additional RMB - * provides LOAD->LOAD order, together they provide LOAD->{LOAD,STORE} order, - * aka. ACQUIRE. */ #ifndef smp_cond_load_acquire #define smp_cond_load_acquire(ptr, cond_expr) ({ \ @@ -329,7 +336,7 @@ static __always_inline void __write_once_size(volatile void *p, void *res, int s break; \ cpu_relax(); \ } \ - smp_rmb(); /* ctrl + rmb := acquire */ \ + smp_acquire__after_ctrl_dep(); \ VAL; \ }) #endif -- cgit v1.2.3 From 7cb45c0fe9858f92cc264f6bf9d2f6a0e7d3b249 Mon Sep 17 00:00:00 2001 From: Peter Zijlstra Date: Wed, 1 Jun 2016 19:23:54 +0200 Subject: locking/barriers: Move smp_cond_load_acquire() to asm-generic/barrier.h Since all asm/barrier.h should/must include asm-generic/barrier.h the latter is a good place for generic infrastructure like this. This also allows archs to override the new smp_acquire__after_ctrl_dep(). Signed-off-by: Peter Zijlstra (Intel) Cc: Andrew Morton Cc: Linus Torvalds Cc: Paul E. McKenney Cc: Peter Zijlstra Cc: Thomas Gleixner Signed-off-by: Ingo Molnar --- include/linux/compiler.h | 37 ------------------------------------- 1 file changed, 37 deletions(-) (limited to 'include/linux/compiler.h') diff --git a/include/linux/compiler.h b/include/linux/compiler.h index 59a7004fc7dd..2e853b679a5d 100644 --- a/include/linux/compiler.h +++ b/include/linux/compiler.h @@ -304,43 +304,6 @@ static __always_inline void __write_once_size(volatile void *p, void *res, int s __u.__val; \ }) -/** - * smp_acquire__after_ctrl_dep() - Provide ACQUIRE ordering after a control dependency - * - * A control dependency provides a LOAD->STORE order, the additional RMB - * provides LOAD->LOAD order, together they provide LOAD->{LOAD,STORE} order, - * aka. (load)-ACQUIRE. - * - * Architectures that do not do load speculation can have this be barrier(). - */ -#define smp_acquire__after_ctrl_dep() smp_rmb() - -/** - * smp_cond_load_acquire() - (Spin) wait for cond with ACQUIRE ordering - * @ptr: pointer to the variable to wait on - * @cond: boolean expression to wait for - * - * Equivalent to using smp_load_acquire() on the condition variable but employs - * the control dependency of the wait to reduce the barrier on many platforms. - * - * Due to C lacking lambda expressions we load the value of *ptr into a - * pre-named variable @VAL to be used in @cond. - */ -#ifndef smp_cond_load_acquire -#define smp_cond_load_acquire(ptr, cond_expr) ({ \ - typeof(ptr) __PTR = (ptr); \ - typeof(*ptr) VAL; \ - for (;;) { \ - VAL = READ_ONCE(*__PTR); \ - if (cond_expr) \ - break; \ - cpu_relax(); \ - } \ - smp_acquire__after_ctrl_dep(); \ - VAL; \ -}) -#endif - #endif /* __KERNEL__ */ #endif /* __ASSEMBLY__ */ -- cgit v1.2.3