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Date: Tue, 25 Nov 2014 13:38:29 +0100 From: Christian Borntraeger <borntraeger@...ibm.com> To: linux-kernel@...r.kernel.org Cc: "linux-arch@...r.kernel.org, linux-mips@...ux-mips.org, linux-x86_64@...r.kernel.org, linux-s390"@vger.kernel.org, Paolo Bonzini <pbonzini@...hat.com>, paulmck@...ux.vnet.ibm.com, mingo@...nel.org, torvalds@...ux-foundation.org, Catalin Marinas <catalin.marinas@....com>, Will Deacon <will.deacon@....com>, Alexei Starovoitov <alexei.starovoitov@...il.com>, David Howells <dhowells@...hat.com>, Russell King <linux@....linux.org.uk>, Christian Borntraeger <borntraeger@...ibm.com> Subject: [PATCHv2 02/10] kernel: Provide READ_ONCE and ASSIGN_ONCE ACCESS_ONCE does not work reliably on non-scalar types. For example gcc 4.6 and 4.7 might remove the volatile tag for such accesses during the SRA (scalar replacement of aggregates) step https://gcc.gnu.org/bugzilla/show_bug.cgi?id=58145) Let's provide READ_ONCE/ASSIGN_ONCE that will do all accesses via scalar types. Signed-off-by: Christian Borntraeger <borntraeger@...ibm.com> --- include/linux/compiler.h | 34 ++++++++++++++++++++++++++++++++++ 1 file changed, 34 insertions(+) diff --git a/include/linux/compiler.h b/include/linux/compiler.h index d5ad7b1..0ff01f2 100644 --- a/include/linux/compiler.h +++ b/include/linux/compiler.h @@ -186,6 +186,40 @@ void ftrace_likely_update(struct ftrace_branch_data *f, int val, int expect); # define __UNIQUE_ID(prefix) __PASTE(__PASTE(__UNIQUE_ID_, prefix), __LINE__) #endif +#include <linux/types.h> + +static __always_inline void __assign_once_size(volatile void *p, void *res, int size) +{ + switch (size) { + case 1: *(volatile u8 *)p = *(u8 *)res; break; + case 2: *(volatile u16 *)p = *(u16 *)res; break; + case 4: *(volatile u32 *)p = *(u32 *)res; break; +#ifdef CONFIG_64BIT + case 8: *(volatile u64 *)p = *(u64 *)res; break; +#endif + } +} + +#define ASSIGN_ONCE(val, p) \ + ({ typeof(p) __val; __val = val; __assign_once_size(&p, &__val, sizeof(__val)); __val; }) + + +static __always_inline void __read_once_size(volatile void *p, void *res, int size) +{ + switch (size) { + case 1: *(u8 *)res = *(volatile u8 *)p; break; + case 2: *(u16 *)res = *(volatile u16 *)p; break; + case 4: *(u32 *)res = *(volatile u32 *)p; break; +#ifdef CONFIG_64BIT + case 8: *(u64 *)res = *(volatile u64 *)p; break; +#endif + } +} + +#define READ_ONCE(p) \ + ({ typeof(p) __val; __read_once_size(&p, &__val, sizeof(__val)); __val; }) + + #endif /* __KERNEL__ */ #endif /* __ASSEMBLY__ */ -- 1.9.3 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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