On Tue, Aug 4, 2015 at 4:53 PM, Konstantin Belousov <kostikbel_at_gmail.com> wrote: > On Tue, Aug 04, 2015 at 04:38:14PM +0200, Luigi Rizzo wrote: >> Hi, >> we have a doubt on the proper way to terminate a kernel thread that >> has been associated to a user process U within a system call with >> >> kthread_add( .. , .., p, ... ) >> >> (p is the struct proc * of the calling process, U) >> >> When U terminates and goes into kern_exit.c :: exit1() >> the kernel thread sees the following conditions: >> >> P_SHOULDSTOP(td->td_proc) is TRUE >> >> td->td_flags has TDF_ASTPENDING | TDF_NEEDSUSPCHK set >> >> We are not sure what is the proper way to terminate >> our kernel thread, whose body is the following: >> >> while (must_run) { // someone will set must_run = 0 >> <check_for_forced_termination> >> kthread_suspend_check(); // void >> work_or_short_tsleep(); // potentially se >> } >> kthread_exit(); >> >> We have seen different ways for the <check_for_forced_termination> >> >> 1. if (P_SHOULDSTOP(td->td_proc) >> break; // kthread_exit() is called outside the loop >> >> 2. if (P_SHOULDSTOP(td->td_proc) >> thread_suspend_check(0); // which then terminates the thread >> // this is done in sys/rpc/svc.c >> >> We are a bit unsure whether calling the thread_*() function in a kthread >> is correct -- but there is an example in the kernel. >> >> Variants involve locking td->td_proc (but is it necessary ? The process >> won't go away until all child threads die), or checking the td_tdflags >> instead of the parent process' flags. >> >> So what is the correct way ? > > If this is a thread of the normal user process, then it is not a kernel > thread, even if it never leaves the kernel mode. thanks for the answer. i do not really know what is the difference between a "kernel thread" and a "thread". Could you clarify what is the distinctive feature between the two ? Perhaps being owned by pid 0 ? This specific thread is created within a system call by invoking kthread_add() and associated with the user process. > > You must call thread_suspend_check() in any in-kernel loop to allow the > stops and process exit to work. so does it mean that the kthread_suspend_check() is incorrect and we should use thread_suspend_check() instead ? cheers luigi -- -----------------------------------------+------------------------------- Prof. Luigi RIZZO, rizzo_at_iet.unipi.it . Dip. di Ing. dell'Informazione http://www.iet.unipi.it/~luigi/ . Universita` di Pisa TEL +39-050-2217533 . via Diotisalvi 2 Mobile +39-338-6809875 . 56122 PISA (Italy) -----------------------------------------+-------------------------------Received on Tue Aug 04 2015 - 13:32:30 UTC
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