kernel/include/linux/posix-timers.h, branch linux-5.11.y

posix-cpu-timers: Provide mechanisms to defer timer handling to task_work

2020-08-06T14:50:59Z

Running posix CPU timers in hard interrupt context has a few downsides: - For PREEMPT_RT it cannot work as the expiry code needs to take sighand lock, which is a 'sleeping spinlock' in RT. The original RT approach of offloading the posix CPU timer handling into a high priority thread was clumsy and provided no real benefit in general. - For fine grained accounting it's just wrong to run this in context of the timer interrupt because that way a process specific CPU time is accounted to the timer interrupt. - Long running timer interrupts caused by a large amount of expiring timers which can be created and armed by unpriviledged user space. There is no hard requirement to expire them in interrupt context. If the signal is targeted at the task itself then it won't be delivered before the task returns to user space anyway. If the signal is targeted at a supervisor process then it might be slightly delayed, but posix CPU timers are inaccurate anyway due to the fact that they are tied to the tick. Provide infrastructure to schedule task work which allows splitting the posix CPU timer code into a quick check in interrupt context and a thread context expiry and signal delivery function. This has to be enabled by architectures as it requires that the architecture specific KVM implementation handles pending task work before exiting to guest mode. Signed-off-by: Thomas Gleixner Signed-off-by: Ingo Molnar Reviewed-by: Oleg Nesterov Acked-by: Peter Zijlstra (Intel) Link: https://lore.kernel.org/r/20200730102337.783470146@linutronix.de

posix-cpu-timers: Store a reference to a pid not a task

2020-03-04T08:54:55Z

posix cpu timers do not handle the death of a process well. This is most clearly seen when a multi-threaded process calls exec from a thread that is not the leader of the thread group. The posix cpu timer code continues to pin the old thread group leader and is unable to find the siglock from there. This results in posix_cpu_timer_del being unable to delete a timer, posix_cpu_timer_set being unable to set a timer. Further to compensate for the problems in posix_cpu_timer_del on a multi-threaded exec all timers that point at the multi-threaded task are stopped. The code for the timers fundamentally needs to check if the target process/thread is alive. This needs an extra level of indirection. This level of indirection is already available in struct pid. So replace cpu.task with cpu.pid to get the needed extra layer of indirection. In addition to handling things more cleanly this reduces the amount of memory a timer can pin when a process exits and then is reaped from a task_struct to the vastly smaller struct pid. Fixes: e0a70217107e ("posix-cpu-timers: workaround to suppress the problems with mt exec") Signed-off-by: "Eric W. Biederman" Signed-off-by: Thomas Gleixner Link: https://lkml.kernel.org/r/87wo86tz6d.fsf@x220.int.ebiederm.org

posix-cpu-timers: Always clear head pointer on dequeue

2019-09-05T19:16:22Z

The head pointer in struct cpu_timer is checked to be NULL in posix_cpu_timer_del() when the delete raced with the exit cleanup. The works correctly as long as the timer is actually dequeued via posix_cpu_timers_exit*(). But if the timer was dequeued due to expiry the head pointer is still set and triggers the warning. In fact keeping the head pointer around after any dequeue is pointless as is has no meaning at all after that. Clear the head pointer always on dequeue and remove the unused requeue function while at it. Fixes: 60bda037f1dd ("posix-cpu-timers: Utilize timerqueue for storage") Reported-by: syzbot+55acd54b57bb4b3840a4@syzkaller.appspotmail.com Signed-off-by: Thomas Gleixner Reviewed-by: Frederic Weisbecker Link: https://lkml.kernel.org/r/20190905120539.707986830@linutronix.de

posix-timers: Unbreak CONFIG_POSIX_TIMERS=n build

2019-08-29T06:25:21Z

The rework of the posix-cpu-timers patch series dropped the empty declaration of struct cpu_timer for the CONFIG_POSIX_TIMERS=n case which causes the build to fail: ./include/linux/posix-timers.h:218:20: error: field 'cpu' has incomplete type Add it back. Fixes: 60bda037f1dd ("posix-cpu-timers: Utilize timerqueue for storage") Reported-by: Ingo Molnar Signed-off-by: Thomas Gleixner

posix-cpu-timers: Utilize timerqueue for storage

2019-08-28T09:50:43Z

Using a linear O(N) search for timer insertion affects execution time and D-cache footprint badly with a larger number of timers. Switch the storage to a timerqueue which is already used for hrtimers and alarmtimers. It does not affect the size of struct k_itimer as it.alarm is still larger. The extra list head for the expiry list will go away later once the expiry is moved into task work context. Signed-off-by: Thomas Gleixner Reviewed-by: Frederic Weisbecker Link: https://lkml.kernel.org/r/alpine.DEB.2.21.1908272129220.1939@nanos.tec.linutronix.de

posix-cpu-timers: Move state tracking to struct posix_cputimers

2019-08-28T09:50:42Z

Put it where it belongs and clean up the ifdeffery in fork completely. Signed-off-by: Thomas Gleixner Link: https://lkml.kernel.org/r/20190821192922.743229404@linutronix.de

posix-cpu-timers: Get rid of zero checks

2019-08-28T09:50:40Z

Deactivation of the expiry cache is done by setting all clock caches to 0. That requires to have a check for zero in all places which update the expiry cache: if (cache == 0 || new < cache) cache = new; Use U64_MAX as the deactivated value, which allows to remove the zero checks when updating the cache and reduces it to the obvious check: if (new < cache) cache = new; This also removes the weird workaround in do_prlimit() which was required to convert a RLIMIT_CPU value of 0 (immediate expiry) to 1 because handing in 0 to the posix CPU timer code would have effectively disarmed it. Signed-off-by: Thomas Gleixner Reviewed-by: Frederic Weisbecker Link: https://lkml.kernel.org/r/20190821192922.275086128@linutronix.de

posix-cpu-timers: Restructure expiry array

2019-08-28T09:50:39Z

Now that the abused struct task_cputime is gone, it's more natural to bundle the expiry cache and the list head of each clock into a struct and have an array of those structs. Follow the hrtimer naming convention of 'bases' and rename the expiry cache to 'nextevt' and adapt all usage sites. Generates also better code .text size shrinks by 80 bytes. Suggested-by: Ingo Molnar Signed-off-by: Thomas Gleixner Reviewed-by: Frederic Weisbecker Link: https://lkml.kernel.org/r/alpine.DEB.2.21.1908262021140.1939@nanos.tec.linutronix.de

posix-cpu-timers: Remove cputime_expires

2019-08-28T09:50:38Z

The last users of the magic struct cputime based expiry cache are gone. Remove the leftovers. Signed-off-by: Thomas Gleixner Reviewed-by: Frederic Weisbecker Link: https://lkml.kernel.org/r/20190821192921.790209622@linutronix.de

posix-cpu-timers: Remove the odd field rename defines

2019-08-28T09:50:37Z

The last users of the odd define based renaming of struct task_cputime members are gone. Good riddance. Signed-off-by: Thomas Gleixner Reviewed-by: Frederic Weisbecker Link: https://lkml.kernel.org/r/20190821192921.499058279@linutronix.de