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/* $OpenBSD: sys_futex.c,v 1.22 2023/08/14 07:42:34 miod Exp $ */
/*
* Copyright (c) 2016-2017 Martin Pieuchot
*
* Permission to use, copy, modify, and distribute this software for any
* purpose with or without fee is hereby granted, provided that the above
* copyright notice and this permission notice appear in all copies.
*
* THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
* WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
* MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
* ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
* WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
* ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
* OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
*/
#include <sys/param.h>
#include <sys/systm.h>
#include <sys/proc.h>
#include <sys/mount.h>
#include <sys/syscallargs.h>
#include <sys/pool.h>
#include <sys/time.h>
#include <sys/rwlock.h>
#include <sys/futex.h>
#ifdef KTRACE
#include <sys/ktrace.h>
#endif
#include <uvm/uvm.h>
/*
* Kernel representation of a futex.
*/
struct futex {
LIST_ENTRY(futex) ft_list; /* list of all futexes */
TAILQ_HEAD(, proc) ft_threads; /* sleeping queue */
struct uvm_object *ft_obj; /* UVM object */
struct vm_amap *ft_amap; /* UVM amap */
voff_t ft_off; /* UVM offset */
unsigned int ft_refcnt; /* # of references */
};
/* Syscall helpers. */
int futex_wait(uint32_t *, uint32_t, const struct timespec *, int);
int futex_wake(uint32_t *, uint32_t, int);
int futex_requeue(uint32_t *, uint32_t, uint32_t *, uint32_t, int);
/* Flags for futex_get(). */
#define FT_CREATE 0x1 /* Create a futex if it doesn't exist. */
#define FT_PRIVATE 0x2 /* Futex is process-private. */
struct futex *futex_get(uint32_t *, int);
void futex_put(struct futex *);
/*
* The global futex lock serializes futex(2) calls so that no wakeup
* event is lost, and protects all futex lists and futex states.
*/
struct rwlock ftlock = RWLOCK_INITIALIZER("futex");
static struct futex_list ftlist_shared =
LIST_HEAD_INITIALIZER(ftlist_shared);
struct pool ftpool;
void
futex_init(void)
{
pool_init(&ftpool, sizeof(struct futex), 0, IPL_NONE,
PR_WAITOK | PR_RWLOCK, "futexpl", NULL);
}
int
sys_futex(struct proc *p, void *v, register_t *retval)
{
struct sys_futex_args /* {
syscallarg(uint32_t *) f;
syscallarg(int) op;
syscallarg(inr) val;
syscallarg(const struct timespec *) timeout;
syscallarg(uint32_t *) g;
} */ *uap = v;
uint32_t *uaddr = SCARG(uap, f);
int op = SCARG(uap, op);
uint32_t val = SCARG(uap, val);
const struct timespec *timeout = SCARG(uap, timeout);
void *g = SCARG(uap, g);
int flags = 0;
int error = 0;
if (op & FUTEX_PRIVATE_FLAG)
flags |= FT_PRIVATE;
rw_enter_write(&ftlock);
switch (op) {
case FUTEX_WAIT:
case FUTEX_WAIT_PRIVATE:
error = futex_wait(uaddr, val, timeout, flags);
break;
case FUTEX_WAKE:
case FUTEX_WAKE_PRIVATE:
*retval = futex_wake(uaddr, val, flags);
break;
case FUTEX_REQUEUE:
case FUTEX_REQUEUE_PRIVATE:
*retval = futex_requeue(uaddr, val, g, (u_long)timeout, flags);
break;
default:
error = ENOSYS;
break;
}
rw_exit_write(&ftlock);
return error;
}
/*
* Return an existing futex matching userspace address ``uaddr''.
*
* If such futex does not exist and FT_CREATE is given, create it.
*/
struct futex *
futex_get(uint32_t *uaddr, int flags)
{
struct proc *p = curproc;
vm_map_t map = &p->p_vmspace->vm_map;
vm_map_entry_t entry;
struct uvm_object *obj = NULL;
struct vm_amap *amap = NULL;
voff_t off = (vaddr_t)uaddr;
struct futex *f;
struct futex_list *ftlist = &p->p_p->ps_ftlist;
rw_assert_wrlock(&ftlock);
if (!(flags & FT_PRIVATE)) {
vm_map_lock_read(map);
if (uvm_map_lookup_entry(map, (vaddr_t)uaddr, &entry) &&
entry->inheritance == MAP_INHERIT_SHARE) {
if (UVM_ET_ISOBJ(entry)) {
ftlist = &ftlist_shared;
obj = entry->object.uvm_obj;
off = entry->offset +
((vaddr_t)uaddr - entry->start);
} else if (entry->aref.ar_amap) {
ftlist = &ftlist_shared;
amap = entry->aref.ar_amap;
off = ptoa(entry->aref.ar_pageoff) +
((vaddr_t)uaddr - entry->start);
}
}
vm_map_unlock_read(map);
}
LIST_FOREACH(f, ftlist, ft_list) {
if (f->ft_obj == obj && f->ft_amap == amap &&
f->ft_off == off) {
f->ft_refcnt++;
break;
}
}
if ((f == NULL) && (flags & FT_CREATE)) {
/*
* We rely on the rwlock to ensure that no other thread
* create the same futex.
*/
f = pool_get(&ftpool, PR_WAITOK);
TAILQ_INIT(&f->ft_threads);
f->ft_obj = obj;
f->ft_amap = amap;
f->ft_off = off;
f->ft_refcnt = 1;
LIST_INSERT_HEAD(ftlist, f, ft_list);
}
return f;
}
/*
* Release a given futex.
*/
void
futex_put(struct futex *f)
{
rw_assert_wrlock(&ftlock);
KASSERT(f->ft_refcnt > 0);
--f->ft_refcnt;
if (f->ft_refcnt == 0) {
KASSERT(TAILQ_EMPTY(&f->ft_threads));
LIST_REMOVE(f, ft_list);
pool_put(&ftpool, f);
}
}
/*
* Put the current thread on the sleep queue of the futex at address
* ``uaddr''. Let it sleep for the specified ``timeout'' time, or
* indefinitely if the argument is NULL.
*/
int
futex_wait(uint32_t *uaddr, uint32_t val, const struct timespec *timeout,
int flags)
{
struct proc *p = curproc;
struct futex *f;
uint64_t nsecs = INFSLP;
uint32_t cval;
int error;
/*
* After reading the value a race is still possible but
* we deal with it by serializing all futex syscalls.
*/
rw_assert_wrlock(&ftlock);
/*
* Read user space futex value
*/
if ((error = copyin32(uaddr, &cval)))
return error;
/* If the value changed, stop here. */
if (cval != val)
return EAGAIN;
if (timeout != NULL) {
struct timespec ts;
if ((error = copyin(timeout, &ts, sizeof(ts))))
return error;
#ifdef KTRACE
if (KTRPOINT(p, KTR_STRUCT))
ktrreltimespec(p, &ts);
#endif
if (ts.tv_sec < 0 || !timespecisvalid(&ts))
return EINVAL;
nsecs = MAX(1, MIN(TIMESPEC_TO_NSEC(&ts), MAXTSLP));
}
f = futex_get(uaddr, flags | FT_CREATE);
TAILQ_INSERT_TAIL(&f->ft_threads, p, p_fut_link);
p->p_futex = f;
error = rwsleep_nsec(p, &ftlock, PWAIT|PCATCH, "fsleep", nsecs);
if (error == ERESTART)
error = ECANCELED;
else if (error == EWOULDBLOCK) {
/* A race occurred between a wakeup and a timeout. */
if (p->p_futex == NULL)
error = 0;
else
error = ETIMEDOUT;
}
/* Remove ourself if we haven't been awaken. */
if ((f = p->p_futex) != NULL) {
p->p_futex = NULL;
TAILQ_REMOVE(&f->ft_threads, p, p_fut_link);
futex_put(f);
}
return error;
}
/*
* Wakeup at most ``n'' sibling threads sleeping on a futex at address
* ``uaddr'' and requeue at most ``m'' sibling threads on a futex at
* address ``uaddr2''.
*/
int
futex_requeue(uint32_t *uaddr, uint32_t n, uint32_t *uaddr2, uint32_t m,
int flags)
{
struct futex *f, *g;
struct proc *p;
uint32_t count = 0;
rw_assert_wrlock(&ftlock);
f = futex_get(uaddr, flags);
if (f == NULL)
return 0;
while ((p = TAILQ_FIRST(&f->ft_threads)) != NULL && (count < (n + m))) {
p->p_futex = NULL;
TAILQ_REMOVE(&f->ft_threads, p, p_fut_link);
futex_put(f);
if (count < n) {
wakeup_one(p);
} else if (uaddr2 != NULL) {
g = futex_get(uaddr2, FT_CREATE);
TAILQ_INSERT_TAIL(&g->ft_threads, p, p_fut_link);
p->p_futex = g;
}
count++;
}
futex_put(f);
return count;
}
/*
* Wakeup at most ``n'' sibling threads sleeping on a futex at address
* ``uaddr''.
*/
int
futex_wake(uint32_t *uaddr, uint32_t n, int flags)
{
return futex_requeue(uaddr, n, NULL, 0, flags);
}
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