until all threads sleeping on a condvar have resumed execution after being
awakened. However, there are cases where that guarantee is very hard to
provide.
thread awakened due to a time out, then cv_waiters was not decremented.
If INT_MAX threads timed out on a cv without an intervening cv_broadcast,
then cv_waiters could overflow. To fix this, have each sleeping thread
decrement cv_waiters when it resumes.
Note that previously cv_waiters was protected by the sleepq chain lock.
However, that lock is not held when threads resume from sleep. In
addition, the interlock is also not always reacquired after resuming
(cv_wait_unlock), nor is it always held by callers of cv_signal() or
cv_broadcast(). Instead, use atomic ops to update cv_waiters. Since
the sleepq chain lock is still held on every increment, it should
still be safe to compare cv_waiters against zero while holding the
lock in the wakeup routines as the only way the race should be lost
would result in extra calls to sleepq_signal() or sleepq_broadcast().
Differential Revision: https://reviews.freebsd.org/D2427
Reviewed by: benno
Reported by: benno (wrap of cv_waiters in the field)
MFC after: 2 weeks
FreeBSD developers need more time to review patches in the surrounding
areas like the TCP stack which are using MPSAFE callouts to restore
distribution of callouts on multiple CPUs.
Bump the __FreeBSD_version instead of reverting it.
Suggested by: kmacy, adrian, glebius and kib
Differential Revision: https://reviews.freebsd.org/D1438
- Close a migration race where callout_reset() failed to set the
CALLOUT_ACTIVE flag.
- Callout callback functions are now allowed to be protected by
spinlocks.
- Switching the callout CPU number cannot always be done on a
per-callout basis. See the updated timeout(9) manual page for more
information.
- The timeout(9) manual page has been updated to reflect how all the
functions inside the callout API are working. The manual page has
been made function oriented to make it easier to deduce how each of
the functions making up the callout API are working without having
to first read the whole manual page. Group all functions into a
handful of sections which should give a quick top-level overview
when the different functions should be used.
- The CALLOUT_SHAREDLOCK flag and its functionality has been removed
to reduce the complexity in the callout code and to avoid problems
about atomically stopping callouts via callout_stop(). If someone
needs it, it can be re-added. From my quick grep there are no
CALLOUT_SHAREDLOCK clients in the kernel.
- A new callout API function named "callout_drain_async()" has been
added. See the updated timeout(9) manual page for a complete
description.
- Update the callout clients in the "kern/" folder to use the callout
API properly, like cv_timedwait(). Previously there was some custom
sleepqueue code in the callout subsystem, which has been removed,
because we now allow callouts to be protected by spinlocks. This
allows us to tear down the callout like done with regular mutexes,
and a "td_slpmutex" has been added to "struct thread" to atomically
teardown the "td_slpcallout". Further the "TDF_TIMOFAIL" and
"SWT_SLEEPQTIMO" states can now be completely removed. Currently
they are marked as available and will be cleaned up in a follow up
commit.
- Bump the __FreeBSD_version to indicate kernel modules need
recompilation.
- There has been several reports that this patch "seems to squash a
serious bug leading to a callout timeout and panic".
Kernel build testing: all architectures were built
MFC after: 2 weeks
Differential Revision: https://reviews.freebsd.org/D1438
Sponsored by: Mellanox Technologies
Reviewed by: jhb, adrian, sbruno and emaste
current lock classes KPI it was really difficult because there was no
way to pass an rmtracker object to the lock/unlock routines. In order
to accomplish the task, modify the aforementioned functions so that
they can return (or pass as argument) an uinptr_t, which is in the rm
case used to hold a pointer to struct rm_priotracker for current
thread. As an added bonus, this fixes rm_sleep() in the rm shared
case, which right now can communicate priotracker structure between
lc_unlock()/lc_lock().
Suggested by: jhb
Reviewed by: jhb
Approved by: re (delphij)
Extend condvar(9) KPI introducing sbt variant of cv_timedwait. This
rely on the previously committed sleepq_set_timeout_sbt().
Sponsored by: Google Summer of Code 2012, iXsystems inc.
Tested by: flo, marius, ian, markj, Fabian Keil
trap checks (eg. printtrap()).
Generally this check is not needed anymore, as there is not a legitimate
case where curthread != NULL, after pcpu 0 area has been properly
initialized.
Reviewed by: bde, jhb
MFC after: 1 week
variable wait routines. DROP_GIANT() already manages that state in the
Giant interlock case.
- Assert that Giant is held when it is passed as a sleep interlock.
msleep/mtx_sleep or the various cv_*wait*() routines. Currently, the
"unlock" behavior of PDROP and cv_wait_unlock() with Giant is not
permitted as it is will be confusing since Giant is fully unrecursed and
unlocked during a thread sleep.
This is handy for subsystems which wish to allow unlocked drivers to
continue to use Giant such as CAM, the new TTY layer, and the new USB
stack. CAM currently uses a hack that I told Scott to use because I
really didn't want to permit this behavior, and the TTY and USB patches
both have various patches to permit this.
MFC after: 2 weeks
routine wakes up proc0 so that proc0 can swap the thread back in.
Historically, this has been done by waking up proc0 directly from
setrunnable() itself via a wakeup(). When waking up a sleeping thread
that was swapped out (the usual case when waking proc0 since only sleeping
threads are eligible to be swapped out), this resulted in a bit of
recursion (e.g. wakeup() -> setrunnable() -> wakeup()).
With sleep queues having separate locks in 6.x and later, this caused a
spin lock LOR (sleepq lock -> sched_lock/thread lock -> sleepq lock).
An attempt was made to fix this in 7.0 by making the proc0 wakeup use
the ithread mechanism for doing the wakeup. However, this required
grabbing proc0's thread lock to perform the wakeup. If proc0 was asleep
elsewhere in the kernel (e.g. waiting for disk I/O), then this degenerated
into the same LOR since the thread lock would be some other sleepq lock.
Fix this by deferring the wakeup of the swapper until after the sleepq
lock held by the upper layer has been locked. The setrunnable() routine
now returns a boolean value to indicate whether or not proc0 needs to be
woken up. The end result is that consumers of the sleepq API such as
*sleep/wakeup, condition variables, sx locks, and lockmgr, have to wakeup
proc0 if they get a non-zero return value from sleepq_abort(),
sleepq_broadcast(), or sleepq_signal().
Discussed with: jeff
Glanced at by: sam
Tested by: Jurgen Weber jurgen - ish com au
MFC after: 2 weeks
sched_sleep(). This removes extra thread_lock() acquisition and
allows the scheduler to decide what to do with the static boost.
- Change the priority arguments to cv_* to match sleepq/msleep/etc.
where 0 means no priority change. Catch -1 in cv_broadcastpri() and
convert it to 0 for now.
- Set a flag when sleeping in a way that is compatible with swapping
since direct priority comparisons are meaningless now.
- Add a sysctl to ule, kern.sched.static_boost, that defaults to on which
controls the boost behavior. Turning it off gives better performance
in some workloads but needs more investigation.
- While we're modifying sleepq, change signal and broadcast to both
return with the lock held as the lock was held on enter.
Reviewed by: jhb, peter
- Adapt sleepqueues to the new thread_lock() mechanism.
- Delay assigning the sleep queue spinlock as the thread lock until after
we've checked for signals. It is illegal for a thread to return in
mi_switch() with any lock assigned to td_lock other than the scheduler
locks.
- Change sleepq_catch_signals() to do the switch if necessary to simplify
the callers.
- Simplify timeout handling now that locking a sleeping thread has the
side-effect of locking the sleepqueue. Some previous races are no
longer possible.
Tested by: kris, current@
Tested on: i386, amd64, ULE, 4BSD, libthr, libkse, PREEMPTION, etc.
Discussed with: kris, attilio, kmacy, jhb, julian, bde (small parts each)
1) adding the thread to the sleepq via sleepq_add() before dropping the
lock, and 2) dropping the sleepq lock around calls to lc_unlock() for
sleepable locks (i.e. locks that use sleepq's in their implementation).
argument from a mutex to a lock_object. Add cv_*wait*() wrapper macros
that accept either a mutex, rwlock, or sx lock as the second argument and
convert it to a lock_object and then call _cv_*wait*(). Basically, the
visible difference is that you can now use rwlocks and sx locks with
condition variables using the same API as with mutexes.
which allows to use it with different kinds of locks. For example it allows
to implement Solaris conditions variables which will be used in ZFS port on
top of sx(9) locks.
Reviewed by: jhb
suspension code. When a thread A is going to sleep, it calls
sleepq_catch_signals() to detect any pending signals or thread
suspension request, if nothing happens, it returns without
holding process lock or scheduler lock, this opens a race
window which allows thread B to come in and do process
suspension work, however since A is still at running state,
thread B can do nothing to A, thread A continues, and puts
itself into actually sleeping state, but B has never seen it,
and it sits there forever until B is woken up by other threads
sometimes later(this can be very long delay or never
happen). Fix this bug by forcing sleepq_catch_signals to
return with scheduler lock held.
Fix sleepq_abort() by passing it an interrupted code, previously,
it worked as wakeup_one(), and the interruption can not be
identified correctly by sleep queue code when the sleeping
thread is resumed.
Let thread_suspend_check() returns EINTR or ERESTART, so sleep
queue no longer has to use SIGSTOP as a hack to build a return
value.
Reviewed by: jhb
MFC after: 1 week
- Implement cv_wait_unlock() method which has semantics compatible
with the sv_wait() method in IRIX. For cv_wait_unlock(), the lock
must be held before entering the function, but is not held when the
function is exited.
- Implement the existing cv_wait() function in terms of cv_wait_unlock().
Submitted by: kan
Feedback from: jhb, trhodes, Christoph Hellwig <hch at infradead dot org>
- Add a new _lock() call to each API that locks the associated chain lock
for a lock_object pointer or wait channel. The _lookup() functions now
require that the chain lock be locked via _lock() when they are called.
- Change sleepq_add(), turnstile_wait() and turnstile_claim() to lookup
the associated queue structure internally via _lookup() rather than
accepting a pointer from the caller. For turnstiles, this means that
the actual lookup of the turnstile in the hash table is only done when
the thread actually blocks rather than being done on each loop iteration
in _mtx_lock_sleep(). For sleep queues, this means that sleepq_lookup()
is no longer used outside of the sleep queue code except to implement an
assertion in cv_destroy().
- Change sleepq_broadcast() and sleepq_signal() to require that the chain
lock is already required. For condition variables, this lets the
cv_broadcast() and cv_signal() functions lock the sleep queue chain lock
while testing the waiters count. This means that the waiters count
internal to condition variables is no longer protected by the interlock
mutex and cv_broadcast() and cv_signal() now no longer require that the
interlock be held when they are called. This lets consumers of condition
variables drop the lock before waking other threads which can result in
fewer context switches.
MFC after: 1 month
have been unified with that of msleep(9), further refine the sleepq
interface and consolidate some duplicated code:
- Move the pre-sleep checks for theaded processes into a
thread_sleep_check() function in kern_thread.c.
- Move all handling of TDF_SINTR to be internal to subr_sleepqueue.c.
Specifically, if a thread is awakened by something other than a signal
while checking for signals before going to sleep, clear TDF_SINTR in
sleepq_catch_signals(). This removes a sched_lock lock/unlock combo in
that edge case during an interruptible sleep. Also, fix
sleepq_check_signals() to properly handle the condition if TDF_SINTR is
clear rather than requiring the callers of the sleepq API to notice
this edge case and call a non-_sig variant of sleepq_wait().
- Clarify the flags arguments to sleepq_add(), sleepq_signal() and
sleepq_broadcast() by creating an explicit submask for sleepq types.
Also, add an explicit SLEEPQ_MSLEEP type rather than a magic number of
0. Also, add a SLEEPQ_INTERRUPTIBLE flag for use with sleepq_add() and
move the setting of TDF_SINTR to sleepq_add() if this flag is set rather
than sleepq_catch_signals(). Note that it is the caller's responsibility
to ensure that sleepq_catch_signals() is called if and only if this flag
is passed to the preceeding sleepq_add(). Note that this also removes a
sched_lock lock/unlock pair from sleepq_catch_signals(). It also ensures
that for an interruptible sleep, TDF_SINTR is always set when
TD_ON_SLEEPQ() is true.
count is protected by the mutex that protects the condition, so the count
does not require any extra locking or atomic operations. It serves as an
optimization to avoid calling into the sleepqueue code at all if there are
no waiters.
Note that the count can get temporarily out of sync when threads sleeping
on a condition variable time out or are aborted. However, it doesn't hurt
to call the sleepqueue code for either a signal or a broadcast when there
are no waiters, and the count is never out of sync in the opposite
direction unless we have more than INT_MAX sleeping threads.
sleep queue interface:
- Sleep queues attempt to merge some of the benefits of both sleep queues
and condition variables. Having sleep qeueus in a hash table avoids
having to allocate a queue head for each wait channel. Thus, struct cv
has shrunk down to just a single char * pointer now. However, the
hash table does not hold threads directly, but queue heads. This means
that once you have located a queue in the hash bucket, you no longer have
to walk the rest of the hash chain looking for threads. Instead, you have
a list of all the threads sleeping on that wait channel.
- Outside of the sleepq code and the sleep/cv code the kernel no longer
differentiates between cv's and sleep/wakeup. For example, calls to
abortsleep() and cv_abort() are replaced with a call to sleepq_abort().
Thus, the TDF_CVWAITQ flag is removed. Also, calls to unsleep() and
cv_waitq_remove() have been replaced with calls to sleepq_remove().
- The sched_sleep() function no longer accepts a priority argument as
sleep's no longer inherently bump the priority. Instead, this is soley
a propery of msleep() which explicitly calls sched_prio() before
blocking.
- The TDF_ONSLEEPQ flag has been dropped as it was never used. The
associated TDF_SET_ONSLEEPQ and TDF_CLR_ON_SLEEPQ macros have also been
dropped and replaced with a single explicit clearing of td_wchan.
TD_SET_ONSLEEPQ() would really have only made sense if it had taken
the wait channel and message as arguments anyway. Now that that only
happens in one place, a macro would be overkill.
SW_INVOL. Assert that one of these is set in mi_switch() and propery
adjust the rusage statistics. This is to simplify the large number of
users of this interface which were previously all required to adjust the
proper counter prior to calling mi_switch(). This also facilitates more
switch and locking optimizations.
- Change all callers of mi_switch() to pass the appropriate paramter and
remove direct references to the process statistics.
thread being waken up. The thread waken up can run at a priority as
high as after tsleep().
- Replace selwakeup()s with selwakeuppri()s and pass appropriate
priorities.
- Add cv_broadcastpri() which raises the priority of the broadcast
threads. Used by selwakeuppri() if collision occurs.
Not objected in: -arch, -current
- Move struct sigacts out of the u-area and malloc() it using the
M_SUBPROC malloc bucket.
- Add a small sigacts_*() API for managing sigacts structures: sigacts_alloc(),
sigacts_free(), sigacts_copy(), sigacts_share(), and sigacts_shared().
- Remove the p_sigignore, p_sigacts, and p_sigcatch macros.
- Add a mutex to struct sigacts that protects all the members of the struct.
- Add sigacts locking.
- Remove Giant from nosys(), kill(), killpg(), and kern_sigaction() now
that sigacts is locked.
- Several in-kernel functions such as psignal(), tdsignal(), trapsignal(),
and thread_stopped() are now MP safe.
Reviewed by: arch@
Approved by: re (rwatson)
td_wmesg field in the thread structure points to the description string of
the condition variable or mutex. If the condvar or the mutex had been
initialized from a loadable module that was unloaded in the meantime,
td_wmesg may now point to invalid memory. Retrieving the process table now
may panic the kernel (or access junk). Setting the td_wmesg field to NULL
after unblocking on the condvar/mutex prevents this panic.
PR: kern/47408
Approved by: jake (mentor)
(show thread {address})
Remove the IDLE kse state and replace it with a change in
the way threads sahre KSEs. Every KSE now has a thread, which is
considered its "owner" however a KSE may also be lent to other
threads in the same group to allow completion of in-kernel work.
n this case the owner remains the same and the KSE will revert to the
owner when the other work has been completed.
All creations of upcalls etc. is now done from
kse_reassign() which in turn is called from mi_switch or
thread_exit(). This means that special code can be removed from
msleep() and cv_wait().
kse_release() does not leave a KSE with no thread any more but
converts the existing thread into teh KSE's owner, and sets it up
for doing an upcall. It is just inhibitted from being scheduled until
there is some reason to do an upcall.
Remove all trace of the kse_idle queue since it is no-longer needed.
"Idle" KSEs are now on the loanable queue.
in specific situations. The owner thread must be blocked, and the
borrower can not proceed back to user space with the borrowed KSE.
The borrower will return the KSE on the next context switch where
teh owner wants it back. This removes a lot of possible
race conditions and deadlocks. It is consceivable that the
borrower should inherit the priority of the owner too.
that's another discussion and would be simple to do.
Also, as part of this, the "preallocatd spare thread" is attached to the
thread doing a syscall rather than the KSE. This removes the need to lock
the scheduler when we want to access it, as it's now "at hand".
DDB now shows a lot mor info for threaded proceses though it may need
some optimisation to squeeze it all back into 80 chars again.
(possible JKH project)
Upcalls are now "bound" threads, but "KSE Lending" now means that
other completing syscalls can be completed using that KSE before the upcall
finally makes it back to the UTS. (getting threads OUT OF THE KERNEL is
one of the highest priorities in the KSE system.) The upcall when it happens
will present all the completed syscalls to the KSE for selection.
be swapped out. Do not put such the thread directly back to the run
queue.
Spotted by: David Xu <davidx@viasoft.com.cn>
While I am here, s/PS_TIMEOUT/TDF_TIMEOUT/.
swapped in, we do not have to ask for the scheduler thread to do
that.
- Assert that a process is not swapped out in runq functions and
swapout().
- Introduce thread_safetoswapout() for readability.
- In swapout_procs(), perform a test that may block (check of a
thread working on its vm map) first. This lets us call swapout()
with the sched_lock held, providing a better atomicity.
except for the fact tha they are presently swapped out. Also add a process
flag to indicate that the process has started the struggle to swap
back in. This will be needed for the case where multiple threads
start the swapin action top a collision. Also add code to stop
a process fropm being swapped out if one of the threads in this
process is actually off running on another CPU.. that might hurt...
Submitted by: Seigo Tanimura <tanimura@r.dl.itc.u-tokyo.ac.jp>
