From 7c756e6e19e71f0327760d8955f7077118ebb2b1 Mon Sep 17 00:00:00 2001 From: Tejun Heo Date: Wed, 24 Jun 2009 15:13:50 +0900 Subject: percpu: implement optional weak percpu definitions Some archs (alpha and s390) need to use weak definitions for percpu variables in modules so that the compiler generates external references for them. This patch implements weak percpu definitions which arch can enable by defining ARCH_NEEDS_WEAK_PER_CPU in arch percpu header file. This weak definition adds the following two restrictions on percpu variable definitions. 1. percpu symbols must be unique whether static or not 2. percpu variables can't be defined inside a function To ensure that these restrictions are observed in generic code, config option DEBUG_FORCE_WEAK_PER_CPU enables weak percpu definitions for all cases. This patch is inspired by Ivan Kokshaysky's alpha percpu patch. [ Impact: stricter rules for percpu variables, one more debug config option ] Signed-off-by: Tejun Heo Cc: Ingo Molnar Cc: David Howells Cc: Ivan Kokshaysky --- include/linux/percpu-defs.h | 65 ++++++++++++++++++++++++++++++++++++++------- 1 file changed, 56 insertions(+), 9 deletions(-) (limited to 'include/linux/percpu-defs.h') diff --git a/include/linux/percpu-defs.h b/include/linux/percpu-defs.h index 8f921d74f49f..cf32838ad0fa 100644 --- a/include/linux/percpu-defs.h +++ b/include/linux/percpu-defs.h @@ -10,21 +10,68 @@ /* * Base implementations of per-CPU variable declarations and definitions, where * the section in which the variable is to be placed is provided by the - * 'section' argument. This may be used to affect the parameters governing the + * 'sec' argument. This may be used to affect the parameters governing the * variable's storage. * * NOTE! The sections for the DECLARE and for the DEFINE must match, lest * linkage errors occur due the compiler generating the wrong code to access * that section. */ -#define DECLARE_PER_CPU_SECTION(type, name, section) \ - extern \ - __attribute__((__section__(PER_CPU_BASE_SECTION section))) \ - PER_CPU_ATTRIBUTES __typeof__(type) per_cpu__##name - -#define DEFINE_PER_CPU_SECTION(type, name, section) \ - __attribute__((__section__(PER_CPU_BASE_SECTION section))) \ - PER_CPU_ATTRIBUTES __typeof__(type) per_cpu__##name +#define __PCPU_ATTRS(sec) \ + __attribute__((section(PER_CPU_BASE_SECTION sec))) \ + PER_CPU_ATTRIBUTES + +#define __PCPU_DUMMY_ATTRS \ + __attribute__((section(".discard"), unused)) + +/* + * s390 and alpha modules require percpu variables to be defined as + * weak to force the compiler to generate GOT based external + * references for them. This is necessary because percpu sections + * will be located outside of the usually addressable area. + * + * This definition puts the following two extra restrictions when + * defining percpu variables. + * + * 1. The symbol must be globally unique, even the static ones. + * 2. Static percpu variables cannot be defined inside a function. + * + * Archs which need weak percpu definitions should define + * ARCH_NEEDS_WEAK_PER_CPU in asm/percpu.h when necessary. + * + * To ensure that the generic code observes the above two + * restrictions, if CONFIG_DEBUG_FORCE_WEAK_PER_CPU is set weak + * definition is used for all cases. + */ +#if defined(ARCH_NEEDS_WEAK_PER_CPU) || defined(CONFIG_DEBUG_FORCE_WEAK_PER_CPU) +/* + * __pcpu_scope_* dummy variable is used to enforce scope. It + * receives the static modifier when it's used in front of + * DEFINE_PER_CPU() and will trigger build failure if + * DECLARE_PER_CPU() is used for the same variable. + * + * __pcpu_unique_* dummy variable is used to enforce symbol uniqueness + * such that hidden weak symbol collision, which will cause unrelated + * variables to share the same address, can be detected during build. + */ +#define DECLARE_PER_CPU_SECTION(type, name, sec) \ + extern __PCPU_DUMMY_ATTRS char __pcpu_scope_##name; \ + extern __PCPU_ATTRS(sec) __weak __typeof__(type) per_cpu__##name + +#define DEFINE_PER_CPU_SECTION(type, name, sec) \ + __PCPU_DUMMY_ATTRS char __pcpu_scope_##name; \ + __PCPU_DUMMY_ATTRS char __pcpu_unique_##name; \ + __PCPU_ATTRS(sec) __weak __typeof__(type) per_cpu__##name +#else +/* + * Normal declaration and definition macros. + */ +#define DECLARE_PER_CPU_SECTION(type, name, sec) \ + extern __PCPU_ATTRS(sec) __typeof__(type) per_cpu__##name + +#define DEFINE_PER_CPU_SECTION(type, name, sec) \ + __PCPU_ATTRS(sec) __typeof__(type) per_cpu__##name +#endif /* * Variant on the per-CPU variable declaration/definition theme used for -- cgit v1.2.3 From 1a8dd307cc0a2119be4e578c517795464e6dabba Mon Sep 17 00:00:00 2001 From: Tejun Heo Date: Mon, 29 Jun 2009 17:45:39 +0900 Subject: percpu: use __weak only in the definition of weak percpu variables __weak is necessary only for definition and might even not work in declaration. Drop it from declaration. This change was suggested by Ivan Kokshaysky. Signed-off-by: Tejun Heo Acked-by: Ivan Kokshaysky --- include/linux/percpu-defs.h | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) (limited to 'include/linux/percpu-defs.h') diff --git a/include/linux/percpu-defs.h b/include/linux/percpu-defs.h index cf32838ad0fa..9b7a53cc16eb 100644 --- a/include/linux/percpu-defs.h +++ b/include/linux/percpu-defs.h @@ -56,7 +56,7 @@ */ #define DECLARE_PER_CPU_SECTION(type, name, sec) \ extern __PCPU_DUMMY_ATTRS char __pcpu_scope_##name; \ - extern __PCPU_ATTRS(sec) __weak __typeof__(type) per_cpu__##name + extern __PCPU_ATTRS(sec) __typeof__(type) per_cpu__##name #define DEFINE_PER_CPU_SECTION(type, name, sec) \ __PCPU_DUMMY_ATTRS char __pcpu_scope_##name; \ -- cgit v1.2.3 From 3e352aa8ee2bd48f1a19c7742810b3a4a7ba605e Mon Sep 17 00:00:00 2001 From: Tejun Heo Date: Mon, 3 Aug 2009 14:10:11 +0900 Subject: x86, percpu: Fix DECLARE/DEFINE_PER_CPU_PAGE_ALIGNED() DECLARE/DEFINE_PER_CPU_PAGE_ALIGNED() put percpu variables in .page_aligned section without adding any alignment restrictions. Currently, this doesn't cause any problem because all users of the macros have explicit page alignment and page-sized but it's much safer to enforce page alignment from the macros. After all, it's what they claim to do. Add __aligned(PAGE_SIZE) to DECLARE/DEFINE_PER_CPU_PAGE_ALIGNED() and drop explicit alignment from it users. Signed-off-by: Tejun Heo Cc: Ingo Molnar Signed-off-by: H. Peter Anvin --- arch/x86/kernel/cpu/common.c | 3 +-- include/linux/percpu-defs.h | 8 +++++--- 2 files changed, 6 insertions(+), 5 deletions(-) (limited to 'include/linux/percpu-defs.h') diff --git a/arch/x86/kernel/cpu/common.c b/arch/x86/kernel/cpu/common.c index f1961c07af9a..12493c5485e5 100644 --- a/arch/x86/kernel/cpu/common.c +++ b/arch/x86/kernel/cpu/common.c @@ -1008,8 +1008,7 @@ static const unsigned int exception_stack_sizes[N_EXCEPTION_STACKS] = { }; static DEFINE_PER_CPU_PAGE_ALIGNED(char, exception_stacks - [(N_EXCEPTION_STACKS - 1) * EXCEPTION_STKSZ + DEBUG_STKSZ]) - __aligned(PAGE_SIZE); + [(N_EXCEPTION_STACKS - 1) * EXCEPTION_STKSZ + DEBUG_STKSZ]); /* May not be marked __init: used by software suspend */ void syscall_init(void) diff --git a/include/linux/percpu-defs.h b/include/linux/percpu-defs.h index 68438e18fff4..afd5f8b7061f 100644 --- a/include/linux/percpu-defs.h +++ b/include/linux/percpu-defs.h @@ -69,11 +69,13 @@ /* * Declaration/definition used for per-CPU variables that must be page aligned. */ -#define DECLARE_PER_CPU_PAGE_ALIGNED(type, name) \ - DECLARE_PER_CPU_SECTION(type, name, ".page_aligned") +#define DECLARE_PER_CPU_PAGE_ALIGNED(type, name) \ + DECLARE_PER_CPU_SECTION(type, name, ".page_aligned") \ + __aligned(PAGE_SIZE) #define DEFINE_PER_CPU_PAGE_ALIGNED(type, name) \ - DEFINE_PER_CPU_SECTION(type, name, ".page_aligned") + DEFINE_PER_CPU_SECTION(type, name, ".page_aligned") \ + __aligned(PAGE_SIZE) /* * Intermodule exports for per-CPU variables. -- cgit v1.2.3 From 53f824520b6d84ca5b4a8fd71addc91dbf64357e Mon Sep 17 00:00:00 2001 From: Jeremy Fitzhardinge Date: Thu, 3 Sep 2009 14:31:44 -0700 Subject: x86/i386: Put aligned stack-canary in percpu shared_aligned section Pack aligned things together into a special section to minimize padding holes. Suggested-by: Eric Dumazet Signed-off-by: Jeremy Fitzhardinge Cc: Tejun Heo LKML-Reference: <4AA035C0.9070202@goop.org> [ queued up in tip:x86/asm because it depends on this commit: x86/i386: Make sure stack-protector segment base is cache aligned ] Signed-off-by: Ingo Molnar --- arch/x86/include/asm/processor.h | 2 +- arch/x86/kernel/cpu/common.c | 2 +- include/asm-generic/percpu.h | 3 +++ include/linux/percpu-defs.h | 8 ++++++++ 4 files changed, 13 insertions(+), 2 deletions(-) (limited to 'include/linux/percpu-defs.h') diff --git a/arch/x86/include/asm/processor.h b/arch/x86/include/asm/processor.h index e597ecc8753c..ac7e79654f3a 100644 --- a/arch/x86/include/asm/processor.h +++ b/arch/x86/include/asm/processor.h @@ -413,7 +413,7 @@ struct stack_canary { char __pad[20]; /* canary at %gs:20 */ unsigned long canary; }; -DECLARE_PER_CPU(struct stack_canary, stack_canary) ____cacheline_aligned; +DECLARE_PER_CPU_ALIGNED(struct stack_canary, stack_canary); #endif #endif /* X86_64 */ diff --git a/arch/x86/kernel/cpu/common.c b/arch/x86/kernel/cpu/common.c index 7d84bc4c1188..f23e236391a3 100644 --- a/arch/x86/kernel/cpu/common.c +++ b/arch/x86/kernel/cpu/common.c @@ -1043,7 +1043,7 @@ DEFINE_PER_CPU(struct orig_ist, orig_ist); #else /* CONFIG_X86_64 */ #ifdef CONFIG_CC_STACKPROTECTOR -DEFINE_PER_CPU(struct stack_canary, stack_canary) ____cacheline_aligned; +DEFINE_PER_CPU_ALIGNED(struct stack_canary, stack_canary); #endif /* Make sure %fs and %gs are initialized properly in idle threads */ diff --git a/include/asm-generic/percpu.h b/include/asm-generic/percpu.h index aa00800adacc..90079c373f1c 100644 --- a/include/asm-generic/percpu.h +++ b/include/asm-generic/percpu.h @@ -81,14 +81,17 @@ extern void setup_per_cpu_areas(void); #ifdef MODULE #define PER_CPU_SHARED_ALIGNED_SECTION "" +#define PER_CPU_ALIGNED_SECTION "" #else #define PER_CPU_SHARED_ALIGNED_SECTION ".shared_aligned" +#define PER_CPU_ALIGNED_SECTION ".shared_aligned" #endif #define PER_CPU_FIRST_SECTION ".first" #else #define PER_CPU_SHARED_ALIGNED_SECTION "" +#define PER_CPU_ALIGNED_SECTION ".shared_aligned" #define PER_CPU_FIRST_SECTION "" #endif diff --git a/include/linux/percpu-defs.h b/include/linux/percpu-defs.h index 68438e18fff4..3058cf9dd3d4 100644 --- a/include/linux/percpu-defs.h +++ b/include/linux/percpu-defs.h @@ -66,6 +66,14 @@ DEFINE_PER_CPU_SECTION(type, name, PER_CPU_SHARED_ALIGNED_SECTION) \ ____cacheline_aligned_in_smp +#define DECLARE_PER_CPU_ALIGNED(type, name) \ + DECLARE_PER_CPU_SECTION(type, name, PER_CPU_ALIGNED_SECTION) \ + ____cacheline_aligned + +#define DEFINE_PER_CPU_ALIGNED(type, name) \ + DEFINE_PER_CPU_SECTION(type, name, PER_CPU_ALIGNED_SECTION) \ + ____cacheline_aligned + /* * Declaration/definition used for per-CPU variables that must be page aligned. */ -- cgit v1.2.3