Date: Sat, 17 Feb 2018 17:07:07 +0100 From: Mateusz Guzik <mjguzik@gmail.com> To: Konstantin Belousov <kostikbel@gmail.com> Cc: Mateusz Guzik <mjg@freebsd.org>, src-committers <src-committers@freebsd.org>, svn-src-all@freebsd.org, svn-src-head@freebsd.org Subject: Re: svn commit: r329448 - head/sys/kern Message-ID: <CAGudoHG%2BXxobj9ziASdW3ugQoxd843K%2BncDSyLbEEGQ20QzAQg@mail.gmail.com> In-Reply-To: <20180217112738.GO94212@kib.kiev.ua> References: <201802170848.w1H8mkfb081764@repo.freebsd.org> <20180217112738.GO94212@kib.kiev.ua>
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On Sat, Feb 17, 2018 at 01:27:38PM +0200, Konstantin Belousov wrote: > On Sat, Feb 17, 2018 at 08:48:46AM +0000, Mateusz Guzik wrote: > > Author: mjg > > Date: Sat Feb 17 08:48:45 2018 > > New Revision: 329448 > > URL: https://svnweb.freebsd.org/changeset/base/329448 > > > > Log: > > exit: get rid of PROC_SLOCK when checking a process to report > Was this tested ? > I was trussing multithreaded microbenchmarks, no issues. > In particular, are you aware of r309539 ? > So it looks like I misread the code - I have grepped thread_suspend_switch operating with the proc locked and misread thread_suspend_one's assert as PROC_LOCK_ASSERT. That said, I think this is harmless. Regardless of the lock the inspecting thread can race and check "too soon". Even for a case where it decides to report, I don't see anything which would depend on the suspending thread to finish. However, locking can be employed in a way which is avoided in the common case: diff --git a/sys/kern/kern_exit.c b/sys/kern/kern_exit.c index b063bda5b7ff..4ae24bcd7059 100644 --- a/sys/kern/kern_exit.c +++ b/sys/kern/kern_exit.c @@ -1174,6 +1174,7 @@ kern_wait6(struct thread *td, idtype_t idtype, id_t id, int *status, struct proc *p, *q; pid_t pid; int error, nfound, ret; + bool report; AUDIT_ARG_VALUE((int)idtype); /* XXX - This is likely wrong! */ AUDIT_ARG_PID((pid_t)id); /* XXX - This may be wrong! */ @@ -1226,27 +1227,36 @@ kern_wait6(struct thread *td, idtype_t idtype, id_t id, int *status, PROC_LOCK_ASSERT(p, MA_OWNED); if ((options & WTRAPPED) != 0 && - (p->p_flag & P_TRACED) != 0 && - (p->p_flag & (P_STOPPED_TRACE | P_STOPPED_SIG)) != 0 && - p->p_suspcount == p->p_numthreads && - (p->p_flag & P_WAITED) == 0) { + (p->p_flag & P_TRACED) != 0) { + PROC_SLOCK(p); + report = + ((p->p_flag & (P_STOPPED_TRACE | P_STOPPED_SIG)) && + p->p_suspcount == p->p_numthreads && + (p->p_flag & P_WAITED) == 0); + PROC_SUNLOCK(p); + if (report) { CTR4(KTR_PTRACE, "wait: returning trapped pid %d status %#x " "(xstat %d) xthread %d", p->p_pid, W_STOPCODE(p->p_xsig), p->p_xsig, p->p_xthread != NULL ? p->p_xthread->td_tid : -1); - report_alive_proc(td, p, siginfo, status, options, - CLD_TRAPPED); - return (0); + report_alive_proc(td, p, siginfo, status, + options, CLD_TRAPPED); + return (0); + } } if ((options & WUNTRACED) != 0 && - (p->p_flag & P_STOPPED_SIG) != 0 && - p->p_suspcount == p->p_numthreads && - (p->p_flag & P_WAITED) == 0) { - report_alive_proc(td, p, siginfo, status, options, + report_alive_proc(td, p, siginfo, status, + options, CLD_TRAPPED); + return (0); + } } if ((options & WUNTRACED) != 0 && - (p->p_flag & P_STOPPED_SIG) != 0 && - p->p_suspcount == p->p_numthreads && - (p->p_flag & P_WAITED) == 0) { - report_alive_proc(td, p, siginfo, status, options, - CLD_STOPPED); - return (0); + (p->p_flag & P_STOPPED_SIG) != 0) { + PROC_SLOCK(p); + report = (p->p_suspcount == p->p_numthreads && + ((p->p_flag & P_WAITED) == 0)); + PROC_SUNLOCK(p); + if (report) { + report_alive_proc(td, p, siginfo, status, + options, CLD_STOPPED); + return (0); + } } if ((options & WCONTINUED) != 0 && (p->p_flag & P_CONTINUED) != 0) { On Sat, Feb 17, 2018 at 12:27 PM, Konstantin Belousov <kostikbel@gmail.com> wrote: > On Sat, Feb 17, 2018 at 08:48:46AM +0000, Mateusz Guzik wrote: > > Author: mjg > > Date: Sat Feb 17 08:48:45 2018 > > New Revision: 329448 > > URL: https://svnweb.freebsd.org/changeset/base/329448 > > > > Log: > > exit: get rid of PROC_SLOCK when checking a process to report > Was this tested ? > > In particular, are you aware of r309539 ? > > > > > All accessed fields are protected with already held process lock. > > > > Modified: > > head/sys/kern/kern_exit.c > > > > Modified: head/sys/kern/kern_exit.c > > ============================================================ > ================== > > --- head/sys/kern/kern_exit.c Sat Feb 17 08:12:35 2018 (r329447) > > +++ head/sys/kern/kern_exit.c Sat Feb 17 08:48:45 2018 (r329448) > > @@ -1228,15 +1228,11 @@ loop_locked: > > nfound++; > > PROC_LOCK_ASSERT(p, MA_OWNED); > > > > - if ((options & (WTRAPPED | WUNTRACED)) != 0) > > - PROC_SLOCK(p); > > - > > if ((options & WTRAPPED) != 0 && > > (p->p_flag & P_TRACED) != 0 && > > (p->p_flag & (P_STOPPED_TRACE | P_STOPPED_SIG)) != 0 && > > p->p_suspcount == p->p_numthreads && > > (p->p_flag & P_WAITED) == 0) { > > - PROC_SUNLOCK(p); > > CTR4(KTR_PTRACE, > > "wait: returning trapped pid %d status %#x " > > "(xstat %d) xthread %d", > > @@ -1251,13 +1247,10 @@ loop_locked: > > (p->p_flag & P_STOPPED_SIG) != 0 && > > p->p_suspcount == p->p_numthreads && > > (p->p_flag & P_WAITED) == 0) { > > - PROC_SUNLOCK(p); > > report_alive_proc(td, p, siginfo, status, options, > > CLD_STOPPED); > > return (0); > > } > > - if ((options & (WTRAPPED | WUNTRACED)) != 0) > > - PROC_SUNLOCK(p); > > if ((options & WCONTINUED) != 0 && > > (p->p_flag & P_CONTINUED) != 0) { > > report_alive_proc(td, p, siginfo, status, options, > -- Mateusz Guzik <mjguzik gmail.com>
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