Date: Sun, 18 Feb 2018 22:08:27 +0100 From: Mateusz Guzik <mjguzik@gmail.com> To: Peter Holm <peter@holm.cc> Cc: Konstantin Belousov <kib@freebsd.org>, 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: <CAGudoHErVG0nj5%2BhHqZNBJM0s%2B=fogdziKWii-KtRqarbGRoWA@mail.gmail.com> In-Reply-To: <20180218204637.GA16922@x2.osted.lan> References: <201802170848.w1H8mkfb081764@repo.freebsd.org> <20180217112738.GO94212@kib.kiev.ua> <CAGudoHG%2BXxobj9ziASdW3ugQoxd843K%2BncDSyLbEEGQ20QzAQg@mail.gmail.com> <20180217162632.GQ94212@kib.kiev.ua> <20180217163822.GA81555@x2.osted.lan> <CAGudoHGUTP28KOvzbPaeHu1j%2Bw7zhtL4H2dMpM58vhi64_=5jg@mail.gmail.com> <20180217184259.GA84054@x2.osted.lan> <CAGudoHH1cNb-czp7X_TdtO1daHoG-ZWXH805T6Qc=rhWDsRiWg@mail.gmail.com> <20180218204637.GA16922@x2.osted.lan>
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Thanks, committed in r329531. On Sun, Feb 18, 2018 at 9:46 PM, Peter Holm <peter@holm.cc> wrote: > On Sat, Feb 17, 2018 at 07:47:38PM +0100, Mateusz Guzik wrote: > > On Sat, Feb 17, 2018 at 7:42 PM, Peter Holm <peter@holm.cc> wrote: > > > > > On Sat, Feb 17, 2018 at 06:34:34PM +0100, Mateusz Guzik wrote: > > > > On Sat, Feb 17, 2018 at 5:38 PM, Peter Holm <peter@holm.cc> wrote: > > > > > > > > > On Sat, Feb 17, 2018 at 06:26:32PM +0200, Konstantin Belousov > wrote: > > > > > > On Sat, Feb 17, 2018 at 05:07:07PM +0100, Mateusz Guzik wrote: > > > > > > > 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. > > > > > > It was definitely not harmless when I tried to avoid the spin > lock > > > there, > > > > > > but I do not remember exact failure mode. Most likely, it was a > > > missed > > > > > > report of the traced child indeed, but I am not sure that truss > > > triggered > > > > > > it. Most likely, Peter Holm was the reporter, since he is > listed in > > > > > > the commit. > > > > > > > > > > > > > > > > I ran a truss(1) test on r329456 and it fails. I have not had a > > > > > chance to look closer at this, but this is what I see: > > > > > > > > > > [root@mercat1 /home/pho]# pgrep truss | xargs ps -Hlp > > > > > UID PID PPID CPU PRI NI VSZ RSS MWCHAN STAT TT TIME > COMMAND > > > > > 0 41149 41118 0 52 0 11532 2588 wait I 0 0:01.38 truss > > > > > /tmp/ttruss 10 > > > > > 0 41151 41149 0 52 0 13156 2300 - TX 0 0:00.98 > > > /tmp/ttruss > > > > > 10 > > > > > 0 41151 41149 0 52 0 13156 2300 - TX 0 0:00.00 > > > /tmp/ttruss > > > > > 10 > > > > > [root@mercat1 /home/pho]# procstat -k 41151 > > > > > PID TID COMM TDNAME KSTACK > > > > > 41151 100211 ttruss - mi_switch > > > > > thread_suspend_switch ptracestop amd64_syscall fast_syscall_common > > > > > 41151 100765 ttruss - mi_switch > > > > > thread_suspend_check ast doreti_ast > > > > > [root@mercat1 /home/pho]# > > > > > > > > > > > > > > Ok, I reproduced the bug with your script. I reverted the change. > > > > > > > > The patch I mailed in this thread fixes it for me. Below is a variant > > > > which can be applied on top of fresh head: > > > > > > > > https://people.freebsd.org/~mjg/wait6_slock.diff > > > > > > > > > > Yes, this also works for me with the truss(1) test scenario. > > > Would you like me to run the full set of test? > > > > > > > > If you have free cycles I don't see why not, thanks. > > > > I ran all of the tests in stress2 on amd64. > No problems found. > > - Peter > -- Mateusz Guzik <mjguzik gmail.com>
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