37a9d912b2
The cmpxchg_futex_value_locked API was funny in that it returned either
the original, user-exposed futex value OR an error code such as -EFAULT.
This was confusing at best, and could be a source of livelocks in places
that retry the cmpxchg_futex_value_locked after trying to fix the issue
by running fault_in_user_writeable().
This change makes the cmpxchg_futex_value_locked API more similar to the
get_futex_value_locked one, returning an error code and updating the
original value through a reference argument.
Signed-off-by: Michel Lespinasse <walken@google.com>
Acked-by: Chris Metcalf <cmetcalf@tilera.com> [tile]
Acked-by: Tony Luck <tony.luck@intel.com> [ia64]
Acked-by: Thomas Gleixner <tglx@linutronix.de>
Tested-by: Michal Simek <monstr@monstr.eu> [microblaze]
Acked-by: David Howells <dhowells@redhat.com> [frv]
Cc: Darren Hart <darren@dvhart.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Matt Turner <mattst88@gmail.com>
Cc: Russell King <linux@arm.linux.org.uk>
Cc: Ralf Baechle <ralf@linux-mips.org>
Cc: "James E.J. Bottomley" <jejb@parisc-linux.org>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: Martin Schwidefsky <schwidefsky@de.ibm.com>
Cc: Paul Mundt <lethal@linux-sh.org>
Cc: "David S. Miller" <davem@davemloft.net>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
LKML-Reference: <20110311024851.GC26122@google.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
128 lines
3.1 KiB
C
128 lines
3.1 KiB
C
#ifndef _ASM_ARM_FUTEX_H
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#define _ASM_ARM_FUTEX_H
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#ifdef __KERNEL__
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#ifdef CONFIG_SMP
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#include <asm-generic/futex.h>
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#else /* !SMP, we can work around lack of atomic ops by disabling preemption */
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#include <linux/futex.h>
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#include <linux/preempt.h>
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#include <linux/uaccess.h>
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#include <asm/errno.h>
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#include <asm/domain.h>
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#define __futex_atomic_op(insn, ret, oldval, uaddr, oparg) \
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__asm__ __volatile__( \
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"1: " T(ldr) " %1, [%2]\n" \
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" " insn "\n" \
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"2: " T(str) " %0, [%2]\n" \
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" mov %0, #0\n" \
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"3:\n" \
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" .pushsection __ex_table,\"a\"\n" \
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" .align 3\n" \
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" .long 1b, 4f, 2b, 4f\n" \
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" .popsection\n" \
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" .pushsection .fixup,\"ax\"\n" \
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"4: mov %0, %4\n" \
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" b 3b\n" \
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" .popsection" \
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: "=&r" (ret), "=&r" (oldval) \
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: "r" (uaddr), "r" (oparg), "Ir" (-EFAULT) \
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: "cc", "memory")
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static inline int
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futex_atomic_op_inuser (int encoded_op, int __user *uaddr)
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{
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int op = (encoded_op >> 28) & 7;
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int cmp = (encoded_op >> 24) & 15;
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int oparg = (encoded_op << 8) >> 20;
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int cmparg = (encoded_op << 20) >> 20;
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int oldval = 0, ret;
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if (encoded_op & (FUTEX_OP_OPARG_SHIFT << 28))
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oparg = 1 << oparg;
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if (!access_ok(VERIFY_WRITE, uaddr, sizeof(int)))
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return -EFAULT;
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pagefault_disable(); /* implies preempt_disable() */
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switch (op) {
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case FUTEX_OP_SET:
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__futex_atomic_op("mov %0, %3", ret, oldval, uaddr, oparg);
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break;
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case FUTEX_OP_ADD:
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__futex_atomic_op("add %0, %1, %3", ret, oldval, uaddr, oparg);
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break;
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case FUTEX_OP_OR:
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__futex_atomic_op("orr %0, %1, %3", ret, oldval, uaddr, oparg);
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break;
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case FUTEX_OP_ANDN:
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__futex_atomic_op("and %0, %1, %3", ret, oldval, uaddr, ~oparg);
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break;
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case FUTEX_OP_XOR:
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__futex_atomic_op("eor %0, %1, %3", ret, oldval, uaddr, oparg);
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break;
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default:
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ret = -ENOSYS;
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}
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pagefault_enable(); /* subsumes preempt_enable() */
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if (!ret) {
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switch (cmp) {
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case FUTEX_OP_CMP_EQ: ret = (oldval == cmparg); break;
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case FUTEX_OP_CMP_NE: ret = (oldval != cmparg); break;
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case FUTEX_OP_CMP_LT: ret = (oldval < cmparg); break;
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case FUTEX_OP_CMP_GE: ret = (oldval >= cmparg); break;
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case FUTEX_OP_CMP_LE: ret = (oldval <= cmparg); break;
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case FUTEX_OP_CMP_GT: ret = (oldval > cmparg); break;
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default: ret = -ENOSYS;
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}
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}
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return ret;
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}
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static inline int
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futex_atomic_cmpxchg_inatomic(int *uval, int __user *uaddr,
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int oldval, int newval)
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{
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int ret = 0, val;
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if (!access_ok(VERIFY_WRITE, uaddr, sizeof(int)))
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return -EFAULT;
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/* Note that preemption is disabled by futex_atomic_cmpxchg_inatomic
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* call sites. */
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__asm__ __volatile__("@futex_atomic_cmpxchg_inatomic\n"
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"1: " T(ldr) " %1, [%4]\n"
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" teq %1, %2\n"
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" it eq @ explicit IT needed for the 2b label\n"
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"2: " T(streq) " %3, [%4]\n"
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"3:\n"
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" .pushsection __ex_table,\"a\"\n"
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" .align 3\n"
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" .long 1b, 4f, 2b, 4f\n"
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" .popsection\n"
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" .pushsection .fixup,\"ax\"\n"
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"4: mov %0, %5\n"
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" b 3b\n"
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" .popsection"
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: "+r" (ret), "=&r" (val)
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: "r" (oldval), "r" (newval), "r" (uaddr), "Ir" (-EFAULT)
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: "cc", "memory");
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*uval = val;
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return ret;
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}
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#endif /* !SMP */
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#endif /* __KERNEL__ */
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#endif /* _ASM_ARM_FUTEX_H */
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