Currently kernel threads use sigprocmask(SIG_BLOCK) to protect against
signals. This doesn't prevent the signal delivery, this only blocks
signal_wake_up(). Every "killall -33 kthreadd" means a "struct siginfo"
leak.
Change kthreadd_setup() to set all handlers to SIG_IGN instead of blocking
them (make a new helper ignore_signals() for that). If the kernel thread
needs some signal, it should use allow_signal() anyway, and in that case it
should not use CLONE_SIGHAND.
Note that we can't change daemonize() (should die!) in the same way,
because it can be used along with CLONE_SIGHAND. This means that
allow_signal() still should unblock the signal to work correctly with
daemonize()ed threads.
However, disallow_signal() doesn't block the signal any longer but ignores
it.
NOTE: with or without this patch the kernel threads are not protected from
handle_stop_signal(), this seems harmless, but not good.
Signed-off-by: Oleg Nesterov <oleg@tv-sign.ru>
Acked-by: "Eric W. Biederman" <ebiederm@xmission.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
When a kernel thread calls daemonize, instead of reparenting the thread to
init reparent the thread to kthreadd next to the threads created by
kthread_create.
This is really just a stop gap until daemonize goes away, but it does
ensure no kernel threads are under init and they are all in one place that
is easy to find.
Signed-off-by: Eric W. Biederman <ebiederm@xmission.com>
Cc: Oleg Nesterov <oleg@tv-sign.ru>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Currently there is a circular reference between work queue initialization
and kthread initialization. This prevents the kthread infrastructure from
initializing until after work queues have been initialized.
We want the properties of tasks created with kthread_create to be as close
as possible to the init_task and to not be contaminated by user processes.
The later we start our kthreadd that creates these tasks the harder it is
to avoid contamination from user processes and the more of a mess we have
to clean up because the defaults have changed on us.
So this patch modifies the kthread support to not use work queues but to
instead use a simple list of structures, and to have kthreadd start from
init_task immediately after our kernel thread that execs /sbin/init.
By being a true child of init_task we only have to change those process
settings that we want to have different from init_task, such as our process
name, the cpus that are allowed, blocking all signals and setting SIGCHLD
to SIG_IGN so that all of our children are reaped automatically.
By being a true child of init_task we also naturally get our ppid set to 0
and do not wind up as a child of PID == 1. Ensuring that tasks generated
by kthread_create will not slow down the functioning of the wait family of
functions.
[akpm@linux-foundation.org: use interruptible sleeps]
Signed-off-by: Eric W. Biederman <ebiederm@xmission.com>
Cc: Oleg Nesterov <oleg@tv-sign.ru>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
____call_usermodehelper() has no reason for flush_signals(). It is a fresh
forked process which is going to exec a user-space application or exit on
failure.
Signed-off-by: Oleg Nesterov <oleg@tv-sign.ru>
Cc: Rusty Russell <rusty@rustcorp.com.au>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
flush_work(wq, work) doesn't need the first parameter, we can use cwq->wq
(this was possible from the very beginnig, I missed this). So we can unify
flush_work_keventd and flush_work.
Also, rename flush_work() to cancel_work_sync() and fix all callers.
Perhaps this is not the best name, but "flush_work" is really bad.
(akpm: this is why the earlier patches bypassed maintainers)
Signed-off-by: Oleg Nesterov <oleg@tv-sign.ru>
Cc: Jeff Garzik <jeff@garzik.org>
Cc: "David S. Miller" <davem@davemloft.net>
Cc: Jens Axboe <jens.axboe@oracle.com>
Cc: Tejun Heo <htejun@gmail.com>
Cc: Auke Kok <auke-jan.h.kok@intel.com>,
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
We already depend on fact that all sub-threads have ->exit_signal == -1, no
need to set it in zap_other_threads().
Signed-off-by: Oleg Nesterov <oleg@tv-sign.ru>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
worker_thread() can miss freeze_process()->signal_wake_up() if it happens
between try_to_freeze() and prepare_to_wait(). We should check freezing()
before entering schedule().
This race was introduced by me in
[PATCH 1/1] workqueue: don't migrate pending works from the dead CPU
Looks like mm/vmscan.c:kswapd() has the same race.
Signed-off-by: Oleg Nesterov <oleg@tv-sign.ru>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
worker_thread() doesn't need to "Block and flush all signals", this was
already done by its caller, kthread().
Signed-off-by: Oleg Nesterov <oleg@tv-sign.ru>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
We don't have any users, and it is not so trivial to use NOAUTOREL works
correctly. It is better to simplify API.
Delete NOAUTOREL support and rename work_release to work_clear_pending to
avoid a confusion.
Signed-off-by: Oleg Nesterov <oleg@tv-sign.ru>
Acked-by: David Howells <dhowells@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
cancel_rearming_delayed_workqueue(wq, dwork) doesn't need the first
parameter. We don't hang on un-queued dwork any longer, and work->data
doesn't change its type. This means we can always figure out "wq" from
dwork when it is needed.
Remove this parameter, and rename the function to
cancel_rearming_delayed_work(). Re-create an inline "obsolete"
cancel_rearming_delayed_workqueue(wq) which just calls
cancel_rearming_delayed_work().
Signed-off-by: Oleg Nesterov <oleg@tv-sign.ru>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Cleanup. A number of per_cpu_ptr(wq->cpu_wq, cpu) users have to check that
cpu is valid for this wq. Make a simple helper.
Signed-off-by: Oleg Nesterov <oleg@tv-sign.ru>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Currently typeof(delayed_work->work.data) is
"struct workqueue_struct" when the timer is pending
"struct cpu_workqueue_struct" whe the work is queued
This makes impossible to use flush_fork(delayed_work->work) in addition
to cancel_delayed_work/cancel_rearming_delayed_work, not good.
Change queue_delayed_work/delayed_work_timer_fn to use cwq, not wq. This
complicates (and uglifies) these functions a little bit, but alows us to
use flush_fork(dwork) and imho makes the whole code more consistent.
Also, document the fact that cancel_rearming_delayed_work() doesn't garantee
the completion of work->func() upon return.
Signed-off-by: Oleg Nesterov <oleg@tv-sign.ru>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
CPU_UP_PREPARE binds cwq->thread to the new CPU. So CPU_UP_CANCELED tries to
wake up the task which is bound to the failed CPU.
With this patch we don't bind cwq->thread until CPU becomes online. The first
wake_up() after kthread_create() is a bit special, make a simple helper for
that.
Signed-off-by: Oleg Nesterov <oleg@tv-sign.ru>
Cc: Gautham R Shenoy <ego@in.ibm.com>
Cc: "Rafael J. Wysocki" <rjw@sisk.pl>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Add explicit workqueue_struct->singlethread flag. This lessens .text a
little, but most importantly this allows us to manipulate wq->list without
changine the meaning of is_single_threaded().
Signed-off-by: Oleg Nesterov <oleg@tv-sign.ru>
Cc: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
The code like
if (is_single_threaded(wq))
do_something(singlethread_cpu);
else {
for_each_cpu_mask(cpu, cpu_populated_map)
do_something(cpu);
}
looks very annoying. We can add "static cpumask_t cpu_singlethread_map" and
simplify the code. Lessens .text a bit, and imho makes the code more readable.
Signed-off-by: Oleg Nesterov <oleg@tv-sign.ru>
Cc: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
cancel_rearming_delayed_workqueue(dwork) will hang forever if dwork was not
scheduled, because in that case cancel_delayed_work()->del_timer_sync() never
returns true.
I don't know if there are any callers which may have problems, but this is not
so convenient, and the fix is very simple.
Q: looks like we don't need "struct workqueue_struct *wq" parameter. If the
timer was aborted successfully, get_wq_data() == wq. Is it worth to add the
new function?
Signed-off-by: Oleg Nesterov <oleg@tv-sign.ru>
Cc: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Because it has no callers.
Actually, I think the whole idea of run_scheduled_work() was not right, not
good to mix "unqueue this work and execute its ->func()" in one function.
Signed-off-by: Oleg Nesterov <oleg@tv-sign.ru>
Cc: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Currently CPU_DEAD uses kthread_stop() to stop cwq->thread and then
transfers cwq->worklist to another CPU. However, it is very unlikely that
worker_thread() will notice kthread_should_stop() before flushing
cwq->worklist. It is only possible if worker_thread() was preempted after
run_workqueue(cwq), a new work_struct was added, and CPU_DEAD happened
before cwq->thread has a chance to run.
This means that take_over_work() mostly adds unneeded complications. Note
also that kthread_stop() is not good per se, wake_up_process() may confuse
work->func() if it sleeps waiting for some event.
Remove take_over_work() and migrate_sequence complications. CPU_DEAD sets
the cwq->should_stop flag (introduced by this patch) and waits for
cwq->thread to flush cwq->worklist and exit. Because the dead CPU is not
on cpu_online_map, no more works can be added to that cwq.
cpu_populated_map was introduced to optimize for_each_possible_cpu(), it is
not strictly needed, and it is more a documentation in fact.
Saves 418 bytes.
Signed-off-by: Oleg Nesterov <oleg@tv-sign.ru>
Cc: Srivatsa Vaddagiri <vatsa@in.ibm.com>
Cc: "Pallipadi, Venkatesh" <venkatesh.pallipadi@intel.com>
Cc: Gautham shenoy <ego@in.ibm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Pointed out by Srivatsa Vaddagiri.
cleanup_workqueue_thread() sets cwq->thread = NULL and does kthread_stop().
This breaks the "if (cwq->thread == current)" logic in flush_cpu_workqueue()
and leads to deadlock.
Kill the thead first, then clear cwq->thread. workqueue_mutex protects us
from create_workqueue_thread() so we don't need cwq->lock.
Signed-off-by: Oleg Nesterov <oleg@tv-sign.ru>
Cc: Srivatsa Vaddagiri <vatsa@in.ibm.com>
Cc: "Pallipadi, Venkatesh" <venkatesh.pallipadi@intel.com>
Cc: Gautham shenoy <ego@in.ibm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Many thanks to Srivatsa Vaddagiri for the helpful discussion and for spotting
the bug in my previous attempt.
work->func() (and thus flush_workqueue()) must not use workqueue_mutex,
this leads to deadlock when CPU_DEAD does kthread_stop(). However without
this mutex held we can't detect CPU_DEAD in progress, which can move pending
works to another CPU while the dead one is not on cpu_online_map.
Change flush_workqueue() to use for_each_possible_cpu(). This means that
flush_cpu_workqueue() may hit CPU which is already dead. However in that
case
!list_empty(&cwq->worklist) || cwq->current_work != NULL
means that CPU_DEAD in progress, it will do kthread_stop() + take_over_work()
so we can proceed and insert a barrier. We hold cwq->lock, so we are safe.
Also, add migrate_sequence incremented by take_over_work() under cwq->lock.
If take_over_work() happened before we checked this CPU, we should see the
new value after spin_unlock().
Further possible changes:
remove CPU_DEAD handling (along with take_over_work, migrate_sequence)
from workqueue.c. CPU_DEAD just sets cwq->please_exit_after_flush flag.
CPU_UP_PREPARE->create_workqueue_thread() clears this flag, and creates
the new thread if cwq->thread == NULL.
This way the workqueue/cpu-hotplug interaction is almost zero, workqueue_mutex
just protects "workqueues" list, CPU_LOCK_ACQUIRE/CPU_LOCK_RELEASE go away.
Signed-off-by: Oleg Nesterov <oleg@tv-sign.ru>
Cc: Srivatsa Vaddagiri <vatsa@in.ibm.com>
Cc: "Pallipadi, Venkatesh" <venkatesh.pallipadi@intel.com>
Cc: Gautham shenoy <ego@in.ibm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
