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kern_module_hook.c
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kern_module_hook.c
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/* $NetBSD: kern_module_hook.c,v 1.4 2019/12/13 08:02:53 skrll Exp $ */
/*-
* Copyright (c) 2019 The NetBSD Foundation, Inc.
* All rights reserved.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions
* are met:
* 1. Redistributions of source code must retain the above copyright
* notice, this list of conditions and the following disclaimer.
* 2. Redistributions in binary form must reproduce the above copyright
* notice, this list of conditions and the following disclaimer in the
* documentation and/or other materials provided with the distribution.
*
* THIS SOFTWARE IS PROVIDED BY THE NETBSD FOUNDATION, INC. AND CONTRIBUTORS
* ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED
* TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
* PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE FOUNDATION OR CONTRIBUTORS
* BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
* CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
* SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
* INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
* CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
* ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
* POSSIBILITY OF SUCH DAMAGE.
*/
/*
* Kernel module support.
*/
#include <sys/cdefs.h>
__KERNEL_RCSID(0, "$NetBSD: kern_module_hook.c,v 1.4 2019/12/13 08:02:53 skrll Exp $");
#include <sys/param.h>
#include <sys/atomic.h>
#include <sys/condvar.h>
#include <sys/module_hook.h>
#include <sys/mutex.h>
#include <sys/pserialize.h>
#include <uvm/uvm_extern.h>
/* Locking/synchronization stuff for module hooks */
static struct {
kmutex_t mtx;
kcondvar_t cv;
pserialize_t psz;
} module_hook __cacheline_aligned;
/*
* We use pserialize_perform() to issue a memory barrier on the current
* CPU and on all other CPUs so that all prior memory operations on the
* current CPU globally happen before all subsequent memory operations
* on the current CPU, as perceived by any other CPU.
*
* pserialize_perform() might be rather heavy-weight here, but it only
* happens during module loading, and it allows MODULE_HOOK_CALL() to
* work without any other memory barriers.
*/
void
module_hook_set(bool *hooked, struct localcount *lc)
{
KASSERT(kernconfig_is_held());
KASSERT(!*hooked);
localcount_init(lc);
/* Wait until setup has been witnessed by all CPUs. */
pserialize_perform(module_hook.psz);
/* Let others use it */
atomic_store_relaxed(hooked, true);
}
void
module_hook_unset(bool *hooked, struct localcount *lc)
{
KASSERT(kernconfig_is_held());
KASSERT(*hooked);
/* Get exclusive with pserialize and localcount. */
mutex_enter(&module_hook.mtx);
/* Prevent new calls to module_hook_tryenter(). */
atomic_store_relaxed(hooked, false);
/* Wait for existing calls to module_hook_tryenter(). */
pserialize_perform(module_hook.psz);
/* Wait for module_hook_exit. */
localcount_drain(lc, &module_hook.cv, &module_hook.mtx);
/* All done! */
mutex_exit(&module_hook.mtx);
localcount_fini(lc);
}
bool
module_hook_tryenter(bool *hooked, struct localcount *lc)
{
bool call_hook;
int s;
s = pserialize_read_enter();
call_hook = atomic_load_relaxed(hooked);
if (call_hook)
localcount_acquire(lc);
pserialize_read_exit(s);
return call_hook;
}
void
module_hook_exit(struct localcount *lc)
{
localcount_release(lc, &module_hook.cv, &module_hook.mtx);
}
void
module_hook_init(void)
{
mutex_init(&module_hook.mtx, MUTEX_DEFAULT, IPL_NONE);
cv_init(&module_hook.cv, "mod_hook");
module_hook.psz = pserialize_create();
}