From: "tip-bot2 for Will Deacon" <tip-bot2@linutronix.de>
To: linux-tip-commits@vger.kernel.org
Cc: Linus Torvalds <torvalds@linux-foundation.org>,
Will Deacon <will@kernel.org>,
Thomas Gleixner <tglx@linutronix.de>,
"Peter Zijlstra (Intel)" <peterz@infradead.org>,
Mark Rutland <mark.rutland@arm.com>,
Michael Ellerman <mpe@ellerman.id.au>,
Arnd Bergmann <arnd@arndb.de>,
Christian Borntraeger <borntraeger@de.ibm.com>,
x86 <x86@kernel.org>, LKML <linux-kernel@vger.kernel.org>
Subject: [tip: locking/kcsan] READ_ONCE: Simplify implementations of {READ,WRITE}_ONCE()
Date: Tue, 12 May 2020 14:36:56 -0000 [thread overview]
Message-ID: <158929421666.390.17077631786357018148.tip-bot2@tip-bot2> (raw)
In-Reply-To: <20200511204150.27858-11-will@kernel.org>
The following commit has been merged into the locking/kcsan branch of tip:
Commit-ID: bbfa112b46bdbbdfc2f5bfb9c2dcbef780ff6417
Gitweb: https://git.kernel.org/tip/bbfa112b46bdbbdfc2f5bfb9c2dcbef780ff6417
Author: Will Deacon <will@kernel.org>
AuthorDate: Mon, 11 May 2020 21:41:42 +01:00
Committer: Thomas Gleixner <tglx@linutronix.de>
CommitterDate: Tue, 12 May 2020 11:04:13 +02:00
READ_ONCE: Simplify implementations of {READ,WRITE}_ONCE()
The implementations of {READ,WRITE}_ONCE() suffer from a significant
amount of indirection and complexity due to a historic GCC bug:
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=58145
which was originally worked around by 230fa253df63 ("kernel: Provide
READ_ONCE and ASSIGN_ONCE").
Since GCC 4.8 is fairly vintage at this point and we emit a warning if
we detect it during the build, return {READ,WRITE}_ONCE() to their former
glory with an implementation that is easier to understand and, crucially,
more amenable to optimisation. A side effect of this simplification is
that WRITE_ONCE() no longer returns a value, but nobody seems to be
relying on that and the new behaviour is aligned with smp_store_release().
Suggested-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Will Deacon <will@kernel.org>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Acked-by: Mark Rutland <mark.rutland@arm.com>
Cc: Michael Ellerman <mpe@ellerman.id.au>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Christian Borntraeger <borntraeger@de.ibm.com>
Link: https://lkml.kernel.org/r/20200511204150.27858-11-will@kernel.org
---
include/linux/compiler.h | 141 ++++++++++++++------------------------
1 file changed, 55 insertions(+), 86 deletions(-)
diff --git a/include/linux/compiler.h b/include/linux/compiler.h
index 9bd0f76..1b4e64d 100644
--- a/include/linux/compiler.h
+++ b/include/linux/compiler.h
@@ -177,28 +177,57 @@ void ftrace_likely_update(struct ftrace_likely_data *f, int val,
# define __UNIQUE_ID(prefix) __PASTE(__PASTE(__UNIQUE_ID_, prefix), __LINE__)
#endif
-#include <uapi/linux/types.h>
+/*
+ * Prevent the compiler from merging or refetching reads or writes. The
+ * compiler is also forbidden from reordering successive instances of
+ * READ_ONCE and WRITE_ONCE, but only when the compiler is aware of some
+ * particular ordering. One way to make the compiler aware of ordering is to
+ * put the two invocations of READ_ONCE or WRITE_ONCE in different C
+ * statements.
+ *
+ * These two macros will also work on aggregate data types like structs or
+ * unions.
+ *
+ * Their two major use cases are: (1) Mediating communication between
+ * process-level code and irq/NMI handlers, all running on the same CPU,
+ * and (2) Ensuring that the compiler does not fold, spindle, or otherwise
+ * mutilate accesses that either do not require ordering or that interact
+ * with an explicit memory barrier or atomic instruction that provides the
+ * required ordering.
+ */
+#include <asm/barrier.h>
+#include <linux/kasan-checks.h>
#include <linux/kcsan-checks.h>
-#define __READ_ONCE_SIZE \
+#define __READ_ONCE(x) (*(volatile typeof(x) *)&(x))
+
+#define READ_ONCE(x) \
({ \
- 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; \
- case 8: *(__u64 *)res = *(volatile __u64 *)p; break; \
- default: \
- barrier(); \
- __builtin_memcpy((void *)res, (const void *)p, size); \
- barrier(); \
- } \
+ typeof(x) *__xp = &(x); \
+ kcsan_check_atomic_read(__xp, sizeof(*__xp)); \
+ __kcsan_disable_current(); \
+ ({ \
+ typeof(x) __x = __READ_ONCE(*__xp); \
+ __kcsan_enable_current(); \
+ smp_read_barrier_depends(); \
+ __x; \
+ }); \
})
+#define WRITE_ONCE(x, val) \
+do { \
+ typeof(x) *__xp = &(x); \
+ kcsan_check_atomic_write(__xp, sizeof(*__xp)); \
+ __kcsan_disable_current(); \
+ *(volatile typeof(x) *)__xp = (val); \
+ __kcsan_enable_current(); \
+} while (0)
+
#ifdef CONFIG_KASAN
/*
- * We can't declare function 'inline' because __no_sanitize_address confilcts
+ * We can't declare function 'inline' because __no_sanitize_address conflicts
* with inlining. Attempt to inline it may cause a build failure.
- * https://gcc.gnu.org/bugzilla/show_bug.cgi?id=67368
+ * https://gcc.gnu.org/bugzilla/show_bug.cgi?id=67368
* '__maybe_unused' allows us to avoid defined-but-not-used warnings.
*/
# define __no_kasan_or_inline __no_sanitize_address notrace __maybe_unused
@@ -225,78 +254,26 @@ void ftrace_likely_update(struct ftrace_likely_data *f, int val,
#define __no_sanitize_or_inline __always_inline
#endif
-static __no_kcsan_or_inline
-void __read_once_size(const volatile void *p, void *res, int size)
-{
- kcsan_check_atomic_read(p, size);
- __READ_ONCE_SIZE;
-}
-
static __no_sanitize_or_inline
-void __read_once_size_nocheck(const volatile void *p, void *res, int size)
+unsigned long __read_once_word_nocheck(const void *addr)
{
- __READ_ONCE_SIZE;
-}
-
-static __no_kcsan_or_inline
-void __write_once_size(volatile void *p, void *res, int size)
-{
- kcsan_check_atomic_write(p, 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;
- case 8: *(volatile __u64 *)p = *(__u64 *)res; break;
- default:
- barrier();
- __builtin_memcpy((void *)p, (const void *)res, size);
- barrier();
- }
+ return __READ_ONCE(*(unsigned long *)addr);
}
/*
- * Prevent the compiler from merging or refetching reads or writes. The
- * compiler is also forbidden from reordering successive instances of
- * READ_ONCE and WRITE_ONCE, but only when the compiler is aware of some
- * particular ordering. One way to make the compiler aware of ordering is to
- * put the two invocations of READ_ONCE or WRITE_ONCE in different C
- * statements.
- *
- * These two macros will also work on aggregate data types like structs or
- * unions. If the size of the accessed data type exceeds the word size of
- * the machine (e.g., 32 bits or 64 bits) READ_ONCE() and WRITE_ONCE() will
- * fall back to memcpy(). There's at least two memcpy()s: one for the
- * __builtin_memcpy() and then one for the macro doing the copy of variable
- * - '__u' allocated on the stack.
- *
- * Their two major use cases are: (1) Mediating communication between
- * process-level code and irq/NMI handlers, all running on the same CPU,
- * and (2) Ensuring that the compiler does not fold, spindle, or otherwise
- * mutilate accesses that either do not require ordering or that interact
- * with an explicit memory barrier or atomic instruction that provides the
- * required ordering.
+ * Use READ_ONCE_NOCHECK() instead of READ_ONCE() if you need to load a
+ * word from memory atomically but without telling KASAN/KCSAN. This is
+ * usually used by unwinding code when walking the stack of a running process.
*/
-#include <asm/barrier.h>
-#include <linux/kasan-checks.h>
-
-#define __READ_ONCE(x, check) \
+#define READ_ONCE_NOCHECK(x) \
({ \
- union { typeof(x) __val; char __c[1]; } __u; \
- if (check) \
- __read_once_size(&(x), __u.__c, sizeof(x)); \
- else \
- __read_once_size_nocheck(&(x), __u.__c, sizeof(x)); \
- smp_read_barrier_depends(); /* Enforce dependency ordering from x */ \
- __u.__val; \
+ unsigned long __x; \
+ compiletime_assert(sizeof(x) == sizeof(__x), \
+ "Unsupported access size for READ_ONCE_NOCHECK()."); \
+ __x = __read_once_word_nocheck(&(x)); \
+ smp_read_barrier_depends(); \
+ __x; \
})
-#define READ_ONCE(x) __READ_ONCE(x, 1)
-
-/*
- * Use READ_ONCE_NOCHECK() instead of READ_ONCE() if you need
- * to hide memory access from KASAN.
- */
-#define READ_ONCE_NOCHECK(x) __READ_ONCE(x, 0)
static __no_kasan_or_inline
unsigned long read_word_at_a_time(const void *addr)
@@ -305,14 +282,6 @@ unsigned long read_word_at_a_time(const void *addr)
return *(unsigned long *)addr;
}
-#define WRITE_ONCE(x, val) \
-({ \
- union { typeof(x) __val; char __c[1]; } __u = \
- { .__val = (__force typeof(x)) (val) }; \
- __write_once_size(&(x), __u.__c, sizeof(x)); \
- __u.__val; \
-})
-
/**
* data_race - mark an expression as containing intentional data races
*
next prev parent reply other threads:[~2020-05-12 14:37 UTC|newest]
Thread overview: 127+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-05-11 20:41 [PATCH v5 00/18] Rework READ_ONCE() to improve codegen Will Deacon
2020-05-11 20:41 ` [PATCH v5 01/18] sparc32: mm: Fix argument checking in __srmmu_get_nocache() Will Deacon
2020-05-12 14:37 ` [tip: locking/kcsan] " tip-bot2 for Will Deacon
2020-05-11 20:41 ` [PATCH v5 02/18] sparc32: mm: Restructure sparc32 MMU page-table layout Will Deacon
2020-05-12 14:37 ` [tip: locking/kcsan] " tip-bot2 for Will Deacon
2020-05-11 20:41 ` [PATCH v5 03/18] sparc32: mm: Change pgtable_t type to pte_t * instead of struct page * Will Deacon
2020-05-12 14:36 ` [tip: locking/kcsan] " tip-bot2 for Will Deacon
2020-05-11 20:41 ` [PATCH v5 04/18] sparc32: mm: Reduce allocation size for PMD and PTE tables Will Deacon
2020-05-12 14:36 ` [tip: locking/kcsan] " tip-bot2 for Will Deacon
2020-05-17 0:00 ` [PATCH v5 04/18] " Guenter Roeck
2020-05-17 0:07 ` Guenter Roeck
2020-05-18 8:37 ` Will Deacon
2020-05-18 9:18 ` Mike Rapoport
2020-05-18 9:48 ` Guenter Roeck
2020-05-18 14:23 ` Mike Rapoport
2020-05-18 16:08 ` Guenter Roeck
2020-05-18 18:11 ` Ira Weiny
2020-05-18 18:14 ` Ira Weiny
2020-05-18 18:09 ` Guenter Roeck
2020-05-18 18:21 ` Ira Weiny
2020-05-18 19:15 ` Mike Rapoport
2020-05-19 16:40 ` Guenter Roeck
2020-05-20 17:03 ` Mike Rapoport
2020-05-20 19:03 ` Guenter Roeck
2020-05-20 19:51 ` Mike Rapoport
2020-05-21 23:02 ` Guenter Roeck
2020-05-24 12:32 ` Mike Rapoport
2020-05-24 14:01 ` Guenter Roeck
2020-05-26 13:26 ` Will Deacon
2020-05-26 14:01 ` Will Deacon
2020-05-26 15:21 ` Mike Rapoport
2020-05-26 16:18 ` Guenter Roeck
2020-05-26 16:29 ` Mike Rapoport
2020-05-26 17:15 ` Guenter Roeck
2020-05-11 20:41 ` [PATCH v5 05/18] compiler/gcc: Raise minimum GCC version for kernel builds to 4.8 Will Deacon
2020-05-12 14:36 ` [tip: locking/kcsan] " tip-bot2 for Will Deacon
2020-05-11 20:41 ` [PATCH v5 06/18] netfilter: Avoid assigning 'const' pointer to non-const pointer Will Deacon
2020-05-12 14:36 ` [tip: locking/kcsan] " tip-bot2 for Will Deacon
2020-05-11 20:41 ` [PATCH v5 07/18] net: tls: " Will Deacon
2020-05-12 14:36 ` [tip: locking/kcsan] " tip-bot2 for Will Deacon
2020-05-11 20:41 ` [PATCH v5 08/18] fault_inject: Don't rely on "return value" from WRITE_ONCE() Will Deacon
2020-05-12 14:36 ` [tip: locking/kcsan] " tip-bot2 for Will Deacon
2020-05-11 20:41 ` [PATCH v5 09/18] arm64: csum: Disable KASAN for do_csum() Will Deacon
2020-05-12 14:36 ` [tip: locking/kcsan] " tip-bot2 for Will Deacon
2020-05-11 20:41 ` [PATCH v5 10/18] READ_ONCE: Simplify implementations of {READ,WRITE}_ONCE() Will Deacon
2020-05-12 14:36 ` tip-bot2 for Will Deacon [this message]
2020-05-11 20:41 ` [PATCH v5 11/18] READ_ONCE: Enforce atomicity for {READ,WRITE}_ONCE() memory accesses Will Deacon
2020-05-12 14:36 ` [tip: locking/kcsan] " tip-bot2 for Will Deacon
2020-05-11 20:41 ` [PATCH v5 12/18] READ_ONCE: Drop pointer qualifiers when reading from scalar types Will Deacon
2020-05-12 14:36 ` [tip: locking/kcsan] " tip-bot2 for Will Deacon
2020-05-11 20:41 ` [PATCH v5 13/18] locking/barriers: Use '__unqual_scalar_typeof' for load-acquire macros Will Deacon
2020-05-12 14:36 ` [tip: locking/kcsan] " tip-bot2 for Will Deacon
2020-05-11 20:41 ` [PATCH v5 14/18] arm64: barrier: Use '__unqual_scalar_typeof' for acquire/release macros Will Deacon
2020-05-12 14:36 ` [tip: locking/kcsan] " tip-bot2 for Will Deacon
2020-05-11 20:41 ` [PATCH v5 15/18] gcov: Remove old GCC 3.4 support Will Deacon
2020-05-12 14:36 ` [tip: locking/kcsan] " tip-bot2 for Will Deacon
2020-05-11 20:41 ` [PATCH v5 16/18] kcsan: Rework data_race() so that it can be used by READ_ONCE() Will Deacon
2020-05-12 14:36 ` [tip: locking/kcsan] " tip-bot2 for Will Deacon
2020-05-11 20:41 ` [PATCH v5 17/18] READ_ONCE: Use data_race() to avoid KCSAN instrumentation Will Deacon
2020-05-12 8:23 ` Peter Zijlstra
2020-05-12 9:49 ` Will Deacon
2020-05-12 14:36 ` [tip: locking/kcsan] " tip-bot2 for Will Deacon
2020-05-20 22:17 ` Borislav Petkov
2020-05-20 22:30 ` Marco Elver
2020-05-21 7:25 ` Borislav Petkov
2020-05-21 9:37 ` Marco Elver
2020-05-21 3:30 ` Nathan Chancellor
2020-05-22 16:08 ` [tip: locking/kcsan] compiler.h: Avoid nested statement expression in data_race() tip-bot2 for Marco Elver
2020-05-11 20:41 ` [PATCH v5 18/18] linux/compiler.h: Remove redundant '#else' Will Deacon
2020-05-12 14:36 ` [tip: locking/kcsan] " tip-bot2 for Will Deacon
2020-05-12 8:18 ` [PATCH v5 00/18] Rework READ_ONCE() to improve codegen Peter Zijlstra
2020-05-12 17:53 ` Marco Elver
2020-05-12 18:55 ` Marco Elver
2020-05-12 19:07 ` Peter Zijlstra
2020-05-12 20:31 ` Marco Elver
2020-05-13 11:10 ` Peter Zijlstra
2020-05-13 11:14 ` Peter Zijlstra
2020-05-13 11:48 ` Marco Elver
2020-05-13 12:32 ` Peter Zijlstra
2020-05-13 12:40 ` Will Deacon
2020-05-13 13:15 ` Marco Elver
2020-05-13 13:24 ` Peter Zijlstra
2020-05-13 13:58 ` Marco Elver
2020-05-14 11:21 ` Peter Zijlstra
2020-05-14 11:24 ` Peter Zijlstra
2020-05-14 11:35 ` Peter Zijlstra
2020-05-14 12:01 ` Will Deacon
2020-05-14 12:27 ` Peter Zijlstra
2020-05-14 13:07 ` Marco Elver
2020-05-14 13:14 ` Peter Zijlstra
2020-05-14 12:20 ` Peter Zijlstra
2020-05-14 14:13 ` Peter Zijlstra
2020-05-14 14:20 ` Marco Elver
2020-05-15 9:20 ` Peter Zijlstra
2020-05-13 16:50 ` Will Deacon
2020-05-13 17:32 ` Marco Elver
2020-05-13 17:47 ` Will Deacon
2020-05-13 18:54 ` Marco Elver
2020-05-13 21:25 ` Will Deacon
2020-05-14 7:31 ` Marco Elver
2020-05-14 11:05 ` Will Deacon
2020-05-14 13:35 ` Marco Elver
2020-05-14 13:47 ` Peter Zijlstra
2020-05-14 13:50 ` Peter Zijlstra
2020-05-14 13:56 ` Peter Zijlstra
2020-05-14 14:24 ` Peter Zijlstra
2020-05-14 15:09 ` Thomas Gleixner
2020-05-14 15:29 ` Marco Elver
2020-05-14 19:37 ` Thomas Gleixner
2020-05-15 13:55 ` David Laight
2020-05-15 14:04 ` Marco Elver
2020-05-15 14:07 ` Peter Zijlstra
2020-05-14 15:38 ` Paul E. McKenney
2020-05-22 16:08 ` [tip: locking/kcsan] kcsan: Restrict supported compilers tip-bot2 for Marco Elver
2020-06-03 18:52 ` [PATCH v5 00/18] Rework READ_ONCE() to improve codegen Borislav Petkov
2020-06-03 19:23 ` Marco Elver
2020-06-03 22:05 ` Borislav Petkov
2020-06-08 17:32 ` Martin Liška
2020-06-08 19:56 ` Marco Elver
2020-06-09 11:55 ` Martin Liška
2020-06-09 12:36 ` Martin Liška
2020-06-09 13:45 ` Marco Elver
2020-05-22 16:08 ` [tip: locking/kcsan] kcsan: Remove 'noinline' from __no_kcsan_or_inline tip-bot2 for Marco Elver
2020-05-13 13:21 ` [PATCH v5 00/18] Rework READ_ONCE() to improve codegen David Laight
2020-05-13 16:32 ` Thomas Gleixner
2020-05-12 21:14 ` Will Deacon
2020-05-12 22:00 ` Marco Elver
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