70a7dd5d5b
Issues were noted by Bruce Evans and are present on all architectures. On i386, a counter fetch should use atomic read of 64bit value, otherwise carry from the increment on other CPU could be lost for the given fetch, making error of 2^32. If 64bit read (cmpxchg8b) is not available on the machine, it cannot be SMP and it is enough to disable preemption around read to avoid the split read. On x86 the counter increment is not atomic on purpose, which makes it possible for the store of the incremented result to override just zeroed per-cpu slot. The effect would be a counter going off by arbitrary value after zeroing. Perform the counter zeroing on the same processor which does the increments, making the operations mutually exclusive. On i386, same as for the fetching, if the cmpxchg8b is not available, machine is not SMP and we disable preemption for zeroing. PowerPC64 is treated the same as amd64. For other architectures, the changes made to allow the compilation to succeed, without fixing the issues with zeroing or fetching. It should be possible to handle them by using the 64bit loads and stores atomic WRT preemption (assuming the architectures also converted from using critical sections to proper asm). If architecture does not provide the facility, using global (spin) mutex would be non-optimal but working solution. Noted by: bde Sponsored by: The FreeBSD Foundation
108 lines
2.7 KiB
C
108 lines
2.7 KiB
C
/*-
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* Copyright (c) 2012 Gleb Smirnoff <glebius@FreeBSD.org>
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* All rights reserved.
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*
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* Redistribution and use in source and binary forms, with or without
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* modification, are permitted provided that the following conditions
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* are met:
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* 1. Redistributions of source code must retain the above copyright
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* notice, this list of conditions and the following disclaimer.
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* 2. Redistributions in binary form must reproduce the above copyright
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* notice, this list of conditions and the following disclaimer in the
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* documentation and/or other materials provided with the distribution.
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*
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* THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
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* ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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* IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
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* ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
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* FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
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* DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
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* OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
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* HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
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* LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
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* OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
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* SUCH DAMAGE.
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*/
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#include <sys/cdefs.h>
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__FBSDID("$FreeBSD$");
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#include <sys/param.h>
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#include <sys/systm.h>
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#include <sys/kernel.h>
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#include <sys/lock.h>
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#include <sys/mutex.h>
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#include <sys/proc.h>
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#include <sys/sched.h>
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#include <sys/smp.h>
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#include <sys/sysctl.h>
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#include <vm/uma.h>
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#define IN_SUBR_COUNTER_C
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#include <sys/counter.h>
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static uma_zone_t uint64_pcpu_zone;
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void
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counter_u64_zero(counter_u64_t c)
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{
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counter_u64_zero_inline(c);
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}
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uint64_t
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counter_u64_fetch(counter_u64_t c)
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{
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return (counter_u64_fetch_inline(c));
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}
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counter_u64_t
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counter_u64_alloc(int flags)
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{
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counter_u64_t r;
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r = uma_zalloc(uint64_pcpu_zone, flags);
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if (r != NULL)
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counter_u64_zero(r);
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return (r);
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}
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void
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counter_u64_free(counter_u64_t c)
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{
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uma_zfree(uint64_pcpu_zone, c);
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}
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int
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sysctl_handle_counter_u64(SYSCTL_HANDLER_ARGS)
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{
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uint64_t out;
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int error;
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out = counter_u64_fetch(*(counter_u64_t *)arg1);
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error = SYSCTL_OUT(req, &out, sizeof(uint64_t));
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if (error || !req->newptr)
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return (error);
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/*
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* Any write attempt to a counter zeroes it.
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*/
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counter_u64_zero(*(counter_u64_t *)arg1);
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return (0);
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}
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static void
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counter_startup(void)
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{
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uint64_pcpu_zone = uma_zcreate("uint64 pcpu", sizeof(uint64_t),
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NULL, NULL, NULL, NULL, UMA_ALIGN_PTR, UMA_ZONE_PCPU);
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}
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SYSINIT(counter, SI_SUB_CPU, SI_ORDER_FOURTH, counter_startup, NULL);
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