/*
* Start or restart a timeout. Installs the callout structure on the
* callwheel. Callers may legally pass any value, even if 0 or negative,
* but since the sc->curticks index may have already been processed a
* minimum timeout of 1 tick will be enforced.
*
* This function will block if the callout is currently queued to a different
* cpu or the callback is currently running in another thread.
*/
void
callout_reset(struct callout *c, int to_ticks, void (*ftn)(void *), void *arg)
{
softclock_pcpu_t sc;
globaldata_t gd;
#ifdef INVARIANTS
if ((c->c_flags & CALLOUT_DID_INIT) == 0) {
callout_init(c);
kprintf(
"callout_reset(%p) from %p: callout was not initialized\n",
c, ((int **)&c)[-1]);
print_backtrace(-1);
}
#endif
gd = mycpu;
sc = &softclock_pcpu_ary[gd->gd_cpuid];
crit_enter_gd(gd);
/*
* Our cpu must gain ownership of the callout and cancel anything
* still running, which is complex. The easiest way to do it is to
* issue a callout_stop().
*
* Clearing bits on flags is a way to guarantee they are not set,
* as the cmpset atomic op will fail otherwise. PENDING and ARMED
* must not be set, if we find them set we loop up and call
* stop_sync() again.
*
*/
for (;;) {
int flags;
int nflags;
callout_stop_sync(c);
flags = c->c_flags & ~(CALLOUT_PENDING | CALLOUT_ARMED);
nflags = (flags & ~(CALLOUT_CPU_MASK |
CALLOUT_EXECUTED)) |
CALLOUT_CPU_TO_FLAGS(gd->gd_cpuid) |
CALLOUT_ARMED |
CALLOUT_PENDING |
CALLOUT_ACTIVE;
if (atomic_cmpset_int(&c->c_flags, flags, nflags))
break;
}
if (to_ticks <= 0)
to_ticks = 1;
c->c_arg = arg;
c->c_func = ftn;
c->c_time = sc->curticks + to_ticks;
TAILQ_INSERT_TAIL(&sc->callwheel[c->c_time & cwheelmask],
c, c_links.tqe);
crit_exit_gd(gd);
}
/*
* Start or restart a timeout. Install the callout structure in the
* callwheel. Callers may legally pass any value, even if 0 or negative,
* but since the sc->curticks index may have already been processed a
* minimum timeout of 1 tick will be enforced.
*
* The callout is installed on and will be processed on the current cpu's
* callout wheel.
*
* WARNING! This function may be called from any cpu but the caller must
* serialize callout_stop() and callout_reset() calls on the passed
* structure regardless of cpu.
*/
void
callout_reset(struct callout *c, int to_ticks, void (*ftn)(void *),
void *arg)
{
softclock_pcpu_t sc;
globaldata_t gd;
#ifdef INVARIANTS
if ((c->c_flags & CALLOUT_DID_INIT) == 0) {
callout_init(c);
kprintf(
"callout_reset(%p) from %p: callout was not initialized\n",
c, ((int **)&c)[-1]);
print_backtrace(-1);
}
#endif
gd = mycpu;
sc = &softclock_pcpu_ary[gd->gd_cpuid];
crit_enter_gd(gd);
if (c->c_flags & CALLOUT_ACTIVE)
callout_stop(c);
if (to_ticks <= 0)
to_ticks = 1;
c->c_arg = arg;
c->c_flags |= (CALLOUT_ACTIVE | CALLOUT_PENDING);
c->c_func = ftn;
c->c_time = sc->curticks + to_ticks;
#ifdef SMP
c->c_gd = gd;
#endif
TAILQ_INSERT_TAIL(&sc->callwheel[c->c_time & callwheelmask],
c, c_links.tqe);
crit_exit_gd(gd);
}
/*
* Stop a running timer. WARNING! If called on a cpu other then the one
* the callout was started on this function will liveloop on its IPI to
* the target cpu to process the request. It is possible for the callout
* to execute in that case.
*
* WARNING! This function may be called from any cpu but the caller must
* serialize callout_stop() and callout_reset() calls on the passed
* structure regardless of cpu.
*
* WARNING! This routine may be called from an IPI
*
* WARNING! This function can return while it's c_func is still running
* in the callout thread, a secondary check may be needed.
* Use callout_stop_sync() to wait for any callout function to
* complete before returning, being sure that no deadlock is
* possible if you do.
*/
int
callout_stop(struct callout *c)
{
globaldata_t gd = mycpu;
globaldata_t tgd;
softclock_pcpu_t sc;
#ifdef INVARIANTS
if ((c->c_flags & CALLOUT_DID_INIT) == 0) {
callout_init(c);
kprintf(
"callout_stop(%p) from %p: callout was not initialized\n",
c, ((int **)&c)[-1]);
print_backtrace(-1);
}
#endif
crit_enter_gd(gd);
/*
* Don't attempt to delete a callout that's not on the queue. The
* callout may not have a cpu assigned to it. Callers do not have
* to be on the issuing cpu but must still serialize access to the
* callout structure.
*
* We are not cpu-localized here and cannot safely modify the
* flags field in the callout structure. Note that most of the
* time CALLOUT_ACTIVE will be 0 if CALLOUT_PENDING is also 0.
*
* If we race another cpu's dispatch of this callout it is possible
* for CALLOUT_ACTIVE to be set with CALLOUT_PENDING unset. This
* will cause us to fall through and synchronize with the other
* cpu.
*/
if ((c->c_flags & CALLOUT_PENDING) == 0) {
if ((c->c_flags & CALLOUT_ACTIVE) == 0) {
crit_exit_gd(gd);
return (0);
}
if (c->c_gd == NULL || c->c_gd == gd) {
c->c_flags &= ~CALLOUT_ACTIVE;
crit_exit_gd(gd);
return (0);
}
}
if ((tgd = c->c_gd) != gd) {
/*
* If the callout is owned by a different CPU we have to
* execute the function synchronously on the target cpu.
*/
int seq;
cpu_ccfence(); /* don't let tgd alias c_gd */
seq = lwkt_send_ipiq(tgd, (void *)callout_stop, c);
lwkt_wait_ipiq(tgd, seq);
} else {
/*
* If the callout is owned by the same CPU we can
* process it directly, but if we are racing our helper
* thread (sc->next), we have to adjust sc->next. The
* race is interlocked by a critical section.
*/
sc = &softclock_pcpu_ary[gd->gd_cpuid];
c->c_flags &= ~(CALLOUT_ACTIVE | CALLOUT_PENDING);
if (sc->next == c)
sc->next = TAILQ_NEXT(c, c_links.tqe);
TAILQ_REMOVE(&sc->callwheel[c->c_time & callwheelmask],
c, c_links.tqe);
c->c_func = NULL;
}
crit_exit_gd(gd);
return (1);
}
/*
* Stop a running timer and ensure that any running callout completes before
* returning. If the timer is running on another cpu this function may block
* to interlock against the callout. If the callout is currently executing
* or blocked in another thread this function may also block to interlock
* against the callout.
*
* The caller must be careful to avoid deadlocks, either by using
* callout_init_lk() (which uses the lockmgr lock cancelation feature),
* by using tokens and dealing with breaks in the serialization, or using
* the lockmgr lock cancelation feature yourself in the callout callback
* function.
*
* callout_stop() returns non-zero if the callout was pending.
*/
static int
_callout_stop(struct callout *c, int issync)
{
globaldata_t gd = mycpu;
globaldata_t tgd;
softclock_pcpu_t sc;
int flags;
int nflags;
int rc;
int cpuid;
#ifdef INVARIANTS
if ((c->c_flags & CALLOUT_DID_INIT) == 0) {
callout_init(c);
kprintf(
"callout_stop(%p) from %p: callout was not initialized\n",
c, ((int **)&c)[-1]);
print_backtrace(-1);
}
#endif
crit_enter_gd(gd);
/*
* Fast path operations:
*
* If ARMED and owned by our cpu, or not ARMED, and other simple
* conditions are met, we can just clear ACTIVE and EXECUTED
* and we are done.
*/
for (;;) {
flags = c->c_flags;
cpu_ccfence();
cpuid = CALLOUT_FLAGS_TO_CPU(flags);
/*
* Can't handle an armed callout in the fast path if it is
* not on the current cpu. We must atomically increment the
* IPI count for the IPI we intend to send and break out of
* the fast path to enter the slow path.
*/
if (flags & CALLOUT_ARMED) {
if (gd->gd_cpuid != cpuid) {
nflags = flags + 1;
if (atomic_cmpset_int(&c->c_flags,
flags, nflags)) {
/* break to slow path */
break;
}
continue; /* retry */
}
} else {
cpuid = gd->gd_cpuid;
KKASSERT((flags & CALLOUT_IPI_MASK) == 0);
KKASSERT((flags & CALLOUT_PENDING) == 0);
}
/*
* Process pending IPIs and retry (only if not called from
* an IPI).
*/
if (flags & CALLOUT_IPI_MASK) {
lwkt_process_ipiq();
continue; /* retry */
}
/*
* Transition to the stopped state, recover the EXECUTED
* status. If pending we cannot clear ARMED until after
* we have removed (c) from the callwheel.
*
* NOTE: The callout might already not be armed but in this
* case it should also not be pending.
*/
nflags = flags & ~(CALLOUT_ACTIVE |
CALLOUT_EXECUTED |
CALLOUT_WAITING |
CALLOUT_PENDING);
/* NOTE: IPI_MASK already tested */
if ((flags & CALLOUT_PENDING) == 0)
nflags &= ~CALLOUT_ARMED;
if (atomic_cmpset_int(&c->c_flags, flags, nflags)) {
/*
* Can only remove from callwheel if currently
* pending.
*/
if (flags & CALLOUT_PENDING) {
sc = &softclock_pcpu_ary[gd->gd_cpuid];
if (sc->next == c)
sc->next = TAILQ_NEXT(c, c_links.tqe);
TAILQ_REMOVE(
&sc->callwheel[c->c_time & cwheelmask],
c,
c_links.tqe);
c->c_func = NULL;
/*
* NOTE: Can't clear ARMED until we have
* physically removed (c) from the
* callwheel.
*
* NOTE: WAITING bit race exists when doing
* unconditional bit clears.
*/
callout_maybe_clear_armed(c);
if (c->c_flags & CALLOUT_WAITING)
flags |= CALLOUT_WAITING;
}
/*
* ARMED has been cleared at this point and (c)
* might now be stale. Only good for wakeup()s.
*/
if (flags & CALLOUT_WAITING)
wakeup(c);
goto skip_slow;
}
/* retry */
}
/*
* Slow path (and not called via an IPI).
*
* When ARMED to a different cpu the stop must be processed on that
* cpu. Issue the IPI and wait for completion. We have already
* incremented the IPI count.
*/
tgd = globaldata_find(cpuid);
lwkt_send_ipiq3(tgd, callout_stop_ipi, c, issync);
for (;;) {
int flags;
int nflags;
flags = c->c_flags;
cpu_ccfence();
if ((flags & CALLOUT_IPI_MASK) == 0) /* fast path */
break;
nflags = flags | CALLOUT_WAITING;
tsleep_interlock(c, 0);
if (atomic_cmpset_int(&c->c_flags, flags, nflags)) {
tsleep(c, PINTERLOCKED, "cstp1", 0);
}
}
skip_slow:
/*
* If (issync) we must also wait for any in-progress callbacks to
* complete, unless the stop is being executed from the callback
* itself. The EXECUTED flag is set prior to the callback
* being made so our existing flags status already has it.
*
* If auto-lock mode is being used, this is where we cancel any
* blocked lock that is potentially preventing the target cpu
* from completing the callback.
*/
while (issync) {
intptr_t *runp;
intptr_t runco;
sc = &softclock_pcpu_ary[cpuid];
if (gd->gd_curthread == &sc->thread) /* stop from cb */
break;
runp = &sc->running;
runco = *runp;
cpu_ccfence();
if ((runco & ~(intptr_t)1) != (intptr_t)c)
break;
if (c->c_flags & CALLOUT_AUTOLOCK)
lockmgr(c->c_lk, LK_CANCEL_BEG);
tsleep_interlock(c, 0);
if (atomic_cmpset_long(runp, runco, runco | 1))
tsleep(c, PINTERLOCKED, "cstp3", 0);
if (c->c_flags & CALLOUT_AUTOLOCK)
lockmgr(c->c_lk, LK_CANCEL_END);
}
crit_exit_gd(gd);
rc = (flags & CALLOUT_EXECUTED) != 0;
return rc;
}
/*
* Setup a callout to run on the specified cpu. Should generally be used
* to run a callout on a specific cpu which does not nominally change.
*/
void
callout_reset_bycpu(struct callout *c, int to_ticks, void (*ftn)(void *),
void *arg, int cpuid)
{
globaldata_t gd;
globaldata_t tgd;
#ifdef INVARIANTS
if ((c->c_flags & CALLOUT_DID_INIT) == 0) {
callout_init(c);
kprintf(
"callout_reset(%p) from %p: callout was not initialized\n",
c, ((int **)&c)[-1]);
print_backtrace(-1);
}
#endif
gd = mycpu;
crit_enter_gd(gd);
tgd = globaldata_find(cpuid);
/*
* Our cpu must temporarily gain ownership of the callout and cancel
* anything still running, which is complex. The easiest way to do
* it is to issue a callout_stop().
*
* Clearing bits on flags (vs nflags) is a way to guarantee they were
* not previously set, by forcing the atomic op to fail. The callout
* must not be pending or armed after the stop_sync, if it is we have
* to loop up and stop_sync() again.
*/
for (;;) {
int flags;
int nflags;
callout_stop_sync(c);
flags = c->c_flags & ~(CALLOUT_PENDING | CALLOUT_ARMED);
nflags = (flags & ~(CALLOUT_CPU_MASK |
CALLOUT_EXECUTED)) |
CALLOUT_CPU_TO_FLAGS(tgd->gd_cpuid) |
CALLOUT_ARMED |
CALLOUT_ACTIVE;
nflags = nflags + 1; /* bump IPI count */
if (atomic_cmpset_int(&c->c_flags, flags, nflags))
break;
cpu_pause();
}
/*
* Even though we are not the cpu that now owns the callout, our
* bumping of the IPI count (and in a situation where the callout is
* not queued to the callwheel) will prevent anyone else from
* depending on or acting on the contents of the callout structure.
*/
if (to_ticks <= 0)
to_ticks = 1;
c->c_arg = arg;
c->c_func = ftn;
c->c_load = to_ticks; /* IPI will add curticks */
lwkt_send_ipiq(tgd, callout_reset_ipi, c);
crit_exit_gd(gd);
}
