Re: [PATCH v2 12/31] arm64: Atomic operations
From: Olof Johansson <hidden>
Date: 2012-08-15 00:21:32
Also in:
linux-arm-kernel, lkml
Hi, On Tue, Aug 14, 2012 at 06:52:13PM +0100, Catalin Marinas wrote:
quoted hunk ↗ jump to hunk
This patch introduces the atomic, mutex and futex operations. Many atomic operations use the load-acquire and store-release operations which imply barriers, avoiding the need for explicit DMB. Signed-off-by: Will Deacon <redacted> Signed-off-by: Catalin Marinas <catalin.marinas@arm.com> --- arch/arm64/include/asm/atomic.h | 306 +++++++++++++++++++++++++++++++++++++++ arch/arm64/include/asm/futex.h | 134 +++++++++++++++++ 2 files changed, 440 insertions(+), 0 deletions(-) create mode 100644 arch/arm64/include/asm/atomic.h create mode 100644 arch/arm64/include/asm/futex.hdiff --git a/arch/arm64/include/asm/atomic.h b/arch/arm64/include/asm/atomic.h new file mode 100644 index 0000000..fa60c8b --- /dev/null +++ b/arch/arm64/include/asm/atomic.h@@ -0,0 +1,306 @@ +/* + * Based on arch/arm/include/asm/atomic.h + * + * Copyright (C) 1996 Russell King. + * Copyright (C) 2002 Deep Blue Solutions Ltd. + * Copyright (C) 2012 ARM Ltd. + * + * This program is free software; you can redistribute it and/or modify + * it under the terms of the GNU General Public License version 2 as + * published by the Free Software Foundation. + * + * This program is distributed in the hope that it will be useful, + * but WITHOUT ANY WARRANTY; without even the implied warranty of + * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the + * GNU General Public License for more details. + * + * You should have received a copy of the GNU General Public License + * along with this program. If not, see <http://www.gnu.org/licenses/>. + */ +#ifndef __ASM_ATOMIC_H +#define __ASM_ATOMIC_H + +#include <linux/compiler.h> +#include <linux/types.h> + +#include <asm/barrier.h> +#include <asm/cmpxchg.h> + +#define ATOMIC_INIT(i) { (i) } + +#ifdef __KERNEL__ + +/* + * On ARM, ordinary assignment (str instruction) doesn't clear the local + * strex/ldrex monitor on some implementations. The reason we can use it for + * atomic_set() is the clrex or dummy strex done on every exception return. + */ +#define atomic_read(v) (*(volatile int *)&(v)->counter) +#define atomic_set(v,i) (((v)->counter) = (i)) + +/* + * AArch64 UP and SMP safe atomic ops. We use load exclusive and + * store exclusive to ensure that these are atomic. We may loop + * to ensure that the update happens. + */ +static inline void atomic_add(int i, atomic_t *v) +{ + unsigned long tmp; + int result; + + asm volatile("// atomic_add\n" +"1: ldxr %w0, [%3]\n" +" add %w0, %w0, %w4\n" +" stxr %w1, %w0, [%3]\n" +" cbnz %w1,1b"
Nit: space before 1b [...]
quoted hunk ↗ jump to hunk
diff --git a/arch/arm64/include/asm/futex.h b/arch/arm64/include/asm/futex.h new file mode 100644 index 0000000..0745e82 --- /dev/null +++ b/arch/arm64/include/asm/futex.h@@ -0,0 +1,134 @@ +/* + * Copyright (C) 2012 ARM Ltd. + * + * This program is free software; you can redistribute it and/or modify + * it under the terms of the GNU General Public License version 2 as + * published by the Free Software Foundation. + * + * This program is distributed in the hope that it will be useful, + * but WITHOUT ANY WARRANTY; without even the implied warranty of + * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the + * GNU General Public License for more details. + * + * You should have received a copy of the GNU General Public License + * along with this program. If not, see <http://www.gnu.org/licenses/>. + */ +#ifndef __ASM_FUTEX_H +#define __ASM_FUTEX_H + +#ifdef __KERNEL__ + +#include <linux/futex.h> +#include <linux/uaccess.h> +#include <asm/errno.h> + +#define __futex_atomic_op(insn, ret, oldval, uaddr, tmp, oparg) \ + asm volatile( \ +"1: ldaxr %w1, %2\n" \ + insn "\n" \ +"2: stlxr %w3, %w0, %2\n" \ +" cbnz %w3, 1b\n" \ +"3: .pushsection __ex_table,\"a\"\n" \ +" .align 3\n" \ +" .quad 1b, 4f, 2b, 4f\n" \ +" .popsection\n" \ +" .pushsection .fixup,\"ax\"\n" \
Moving the exception table below the body of the code makes the flow easier to read, please do that. Also, don't you need a barrier here?
+"4: mov %w0, %w5\n" \
+" b 3b\n" \
+" .popsection" \
+ : "=&r" (ret), "=&r" (oldval), "+Q" (*uaddr), "=&r" (tmp) \
+ : "r" (oparg), "Ir" (-EFAULT) \
+ : "cc")
+
+static inline int
+futex_atomic_op_inuser (int encoded_op, u32 __user *uaddr)
+{
+ int op = (encoded_op >> 28) & 7;
+ int cmp = (encoded_op >> 24) & 15;
+ int oparg = (encoded_op << 8) >> 20;
+ int cmparg = (encoded_op << 20) >> 20;
+ int oldval = 0, ret, tmp;
+
+ if (encoded_op & (FUTEX_OP_OPARG_SHIFT << 28))
+ oparg = 1 << oparg;
+
+ if (!access_ok(VERIFY_WRITE, uaddr, sizeof(u32)))
+ return -EFAULT;
+
+ pagefault_disable(); /* implies preempt_disable() */
+
+ switch (op) {
+ case FUTEX_OP_SET:
+ __futex_atomic_op("mov %w0, %w4",
+ ret, oldval, uaddr, tmp, oparg);
+ break;
+ case FUTEX_OP_ADD:
+ __futex_atomic_op("add %w0, %w1, %w4",
+ ret, oldval, uaddr, tmp, oparg);
+ break;
+ case FUTEX_OP_OR:
+ __futex_atomic_op("orr %w0, %w1, %w4",
+ ret, oldval, uaddr, tmp, oparg);
+ break;
+ case FUTEX_OP_ANDN:
+ __futex_atomic_op("and %w0, %w1, %w4",
+ ret, oldval, uaddr, tmp, ~oparg);
+ break;
+ case FUTEX_OP_XOR:
+ __futex_atomic_op("eor %w0, %w1, %w4",
+ ret, oldval, uaddr, tmp, oparg);
+ break;
+ default:
+ ret = -ENOSYS;
+ }
+
+ pagefault_enable(); /* subsumes preempt_enable() */
+
+ if (!ret) {
+ switch (cmp) {
+ case FUTEX_OP_CMP_EQ: ret = (oldval == cmparg); break;
+ case FUTEX_OP_CMP_NE: ret = (oldval != cmparg); break;
+ case FUTEX_OP_CMP_LT: ret = (oldval < cmparg); break;
+ case FUTEX_OP_CMP_GE: ret = (oldval >= cmparg); break;
+ case FUTEX_OP_CMP_LE: ret = (oldval <= cmparg); break;
+ case FUTEX_OP_CMP_GT: ret = (oldval > cmparg); break;
+ default: ret = -ENOSYS;
+ }
+ }
+ return ret;
+}
+
+static inline int
+futex_atomic_cmpxchg_inatomic(u32 *uval, u32 __user *uaddr,
+ u32 oldval, u32 newval)
+{
+ int ret = 0;
+ u32 val, tmp;
+
+ if (!access_ok(VERIFY_WRITE, uaddr, sizeof(u32)))
+ return -EFAULT;
+
+ asm volatile("// futex_atomic_cmpxchg_inatomic\n"
+"1: ldaxr %w1, %2\n"
+" sub %w3, %w1, %w4\n"
+" cbnz %w3, 3f\n"
+"2: stlxr %w3, %w5, %2\n"
+" cbnz %w3, 1b\n"
+"3: .pushsection __ex_table,\"a\"\n"
+" .align 3\n"
+" .quad 1b, 4f, 2b, 4f\n"
+" .popsection\n"
+" .pushsection .fixup,\"ax\"\n"Same here w.r.t. exception table location and barrier.
+"4: mov %w0, %w6\n" +" b 3b\n" +" .popsection" + : "+r" (ret), "=&r" (val), "+Q" (*uaddr), "=&r" (tmp) + : "r" (oldval), "r" (newval), "Ir" (-EFAULT) + : "cc", "memory"); + + *uval = val; + return ret; +} + +#endif /* __KERNEL__ */ +#endif /* __ASM_FUTEX_H */
-Olof