Date: Wed, 1 Sep 2021 11:49:07 -0600 From: Warner Losh <imp@bsdimp.com> To: Ian Lepore <ian@freebsd.org> Cc: Craig Leres <leres@freebsd.org>, FreeBSD Hackers <freebsd-hackers@freebsd.org> Subject: Re: Patched gpsd and /dev/pps0 results in "sleeping thread" kernel panic Message-ID: <CANCZdfppCc9mdJP=kZxtnt_ME2zaGvq=jcqpHHx6r_Rxbfvz5A@mail.gmail.com> In-Reply-To: <5d812d36e5291af35ecadf910a6d5f76b60f1441.camel@freebsd.org> References: <dc4c4948-738e-c530-d96f-ade5cce5d3d2@freebsd.org> <CANCZdfos2NamQXXcjYyVAcJvUL21kQbjUR4KRTp1xXKsQN3SrA@mail.gmail.com> <5476ea21-9e8a-32f5-08ff-add46c02d910@freebsd.org> <CANCZdfoQTfWC4j=ArTdGQMwDDNsg-LMMYSrtF4BHtHZSuV%2BCkw@mail.gmail.com> <cd29114478b51ca577308dfaacd9df076813a313.camel@freebsd.org> <CANCZdfrkg9dKKoLqpEX285eYPspciNj2eeH8RVZEtAr9Nc1SBQ@mail.gmail.com> <CANCZdfrDsEotO36eE%2BUUvUxAWq=_3pQ9NivGU=_r=%2BikWdUQXw@mail.gmail.com> <5d812d36e5291af35ecadf910a6d5f76b60f1441.camel@freebsd.org>
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--00000000000072604805caf2afba Content-Type: text/plain; charset="UTF-8" On Wed, Sep 1, 2021 at 9:07 AM Ian Lepore <ian@freebsd.org> wrote: > On Tue, 2021-08-31 at 22:35 -0600, Warner Losh wrote: > > On Tue, Aug 31, 2021 at 9:25 PM Warner Losh <imp@bsdimp.com> wrote: > > > > > > > > > > > On Tue, Aug 31, 2021 at 9:13 PM Ian Lepore <ian@freebsd.org> wrote: > > > > > > > On Tue, 2021-08-31 at 21:07 -0600, Warner Losh wrote: > > > > > On Tue, Aug 31, 2021 at 8:11 PM Craig Leres <leres@freebsd.org> > > > > > wrote: > > > > > > > > > > > > > > > > > On 8/31/21 6:54 PM, Warner Losh wrote: > > > > > > > Can you post a traceback? We recently tightened up the > > > > > > > sleeping > > > > > > conditions > > > > > > > and many of the panics are straight forward to fix > > > > > > > > > > > > Is this sufficient? > > > > > > > > > > > > > > > > Maybe. I'm guessing that the pps driver isn't setting > > > > > driver_mtx for > > > > > the > > > > > pps_state that it keeps, so when we're sleeping in pps_ioctl > > > > > we're > > > > > not > > > > > dropping the the ppbus lock, which leads to this diagnostic. > > > > > > > > > > Warner > > > > > > > > > > > > > > > > > > > > > > Exactly so, I've just been digging through the code. It's not an > > > > easy > > > > fix because the ppbus pps driver doesn't have access to the ppbus > > > > mutex > > > > at the point where it's registering to be a pps driver. > > > > > > > > > > I just came to the conclusion that either we'd need to create a > > > call in > > > ppbus > > > to set this mutex, or to return its lock... > > > > > > > > > > Craig, is there any chance you can configure your hardware so > > > > that the > > > > PPS signal is connected to either the CTS or DCD pin of a uart > > > > (even > > > > the same uart that's communicating with the gps receiver should > > > > work if > > > > you use DCD)? You'll get jitter and accuracy performance > > > > comparable to > > > > the parallel port pin, and avoid this mutex/sleeping problem. > > > > > > > > > > That's easier, but depending on the hardware might be harder :( > > > > > > > Either I'm missing something (likely am), or this might fix it up, > > or at least get away from the warning: > > > > https://reviews.freebsd.org/D31763 > > > > Note: I can't recall why ppbus has to be locked for this call. > > This code dates from the very earliest days of locking and > > so may do things simply because it seemed like a good idea > > without a specific notion as to what that lock is protecting. If > > so, the real fix may be to not take the lock in pps_ioctl at > > all and maybe instead use a reference count (the most > > often reason for 'a good idea' was to keep the device > > from going away, though this is a parent lock, not a > > child one so I'm less sure about that being the reason). > > > > Warner > > > > > > Yeah, figuring out whether it's safe to drop/re-aquire the ppsbus lock > at this point was the harder part of the work; I'm not very familiar > with the ppsbus stuff in general. > > Warner, I pointed out a small change needed to your proposed patch in > D31763. In the past I've found that one can't propose a different > patch in Phab without commandeering the entire change, so I just posted > an inline comment with the couple extra lines of code needed, hoping > you have more time today than I do to prepare a new patch. > I've updated the patch. Please review it and make sure I got it right. It was the same one that Craig came up with and tested as well. I'll commit if things are good and get into my MFC queue. Warner > -- Ian > > > > > Warner > > > > > > > > > > -- Ian > > > > > > > > > > > > > > > > > > Craig > > > > > > > > > > > > toc2 4 # kgdb /boot/kernel/kernel /var/crash/vmcore.1 > > > > > > GNU gdb (GDB) 10.2 [GDB v10.2 for FreeBSD] > > > > > > Copyright (C) 2021 Free Software Foundation, Inc. > > > > > > License GPLv3+: GNU GPL version 3 or later > > > > > > <http://gnu.org/licenses/gpl.html>; > > > > > > This is free software: you are free to change and > > > > > > redistribute it. > > > > > > There is NO WARRANTY, to the extent permitted by law. > > > > > > Type "show copying" and "show warranty" for details. > > > > > > This GDB was configured as "x86_64-portbld-freebsd12.2". > > > > > > Type "show configuration" for configuration details. > > > > > > For bug reporting instructions, please see: > > > > > > <https://www.gnu.org/software/gdb/bugs/>. > > > > > > Find the GDB manual and other documentation resources online > > > > > > at: > > > > > > <http://www.gnu.org/software/gdb/documentation/>. > > > > > > > > > > > > For help, type "help". > > > > > > Type "apropos word" to search for commands related to > > > > > > "word"... > > > > > > Reading symbols from /boot/kernel/kernel... > > > > > > Reading symbols from /boot/kernel.LBLNET/kernel.debug... > > > > > > > > > > > > Unread portion of the kernel message buffer: > > > > > > Sleeping thread (tid 101408, pid 2046) owns a non-sleepable > > > > > > lock > > > > > > KDB: stack backtrace of thread 101408: > > > > > > sched_switch() at sched_switch+0x630/frame 0xfffffe0070e4f760 > > > > > > mi_switch() at mi_switch+0xd4/frame 0xfffffe0070e4f790 > > > > > > sleepq_catch_signals() at sleepq_catch_signals+0x403/frame > > > > > > 0xfffffe0070e4f7e0 > > > > > > sleepq_timedwait_sig() at sleepq_timedwait_sig+0x14/frame > > > > > > 0xfffffe0070e4f820 > > > > > > _sleep() at _sleep+0x1b3/frame 0xfffffe0070e4f8a0 > > > > > > pps_ioctl() at pps_ioctl+0x298/frame 0xfffffe0070e4f8f0 > > > > > > ppsioctl() at ppsioctl+0x48/frame 0xfffffe0070e4f920 > > > > > > devfs_ioctl() at devfs_ioctl+0xb0/frame 0xfffffe0070e4f970 > > > > > > VOP_IOCTL_APV() at VOP_IOCTL_APV+0x7b/frame > > > > > > 0xfffffe0070e4f9a0 > > > > > > vn_ioctl() at vn_ioctl+0x16a/frame 0xfffffe0070e4fab0 > > > > > > devfs_ioctl_f() at devfs_ioctl_f+0x1e/frame > > > > > > 0xfffffe0070e4fad0 > > > > > > kern_ioctl() at kern_ioctl+0x2b7/frame 0xfffffe0070e4fb30 > > > > > > sys_ioctl() at sys_ioctl+0xfa/frame 0xfffffe0070e4fc00 > > > > > > amd64_syscall() at amd64_syscall+0x387/frame > > > > > > 0xfffffe0070e4fd30 > > > > > > fast_syscall_common() at fast_syscall_common+0xf8/frame > > > > > > 0xfffffe0070e4fd30 > > > > > > --- syscall (54, FreeBSD ELF64, sys_ioctl), rip = > > > > > > 0x8004c899a, rsp > > > > > > = > > > > > > 0x7fffdfdfc6a8, rbp = 0x7fffdfdfc730 --- > > > > > > panic: sleeping thread > > > > > > cpuid = 8 > > > > > > time = 1630456142 > > > > > > KDB: stack backtrace: > > > > > > db_trace_self_wrapper() at db_trace_self_wrapper+0x2b/frame > > > > > > 0xfffffe005ab73ab0 > > > > > > vpanic() at vpanic+0x17b/frame 0xfffffe005ab73b00 > > > > > > panic() at panic+0x43/frame 0xfffffe005ab73b60 > > > > > > propagate_priority() at propagate_priority+0x282/frame > > > > > > 0xfffffe005ab73b90 > > > > > > turnstile_wait() at turnstile_wait+0x30c/frame > > > > > > 0xfffffe005ab73be0 > > > > > > __mtx_lock_sleep() at __mtx_lock_sleep+0x199/frame > > > > > > 0xfffffe005ab73c70 > > > > > > ppcintr() at ppcintr+0x2a0/frame 0xfffffe005ab73c90 > > > > > > ithread_loop() at ithread_loop+0x23c/frame 0xfffffe005ab73cf0 > > > > > > fork_exit() at fork_exit+0x7e/frame 0xfffffe005ab73d30 > > > > > > fork_trampoline() at fork_trampoline+0xe/frame > > > > > > 0xfffffe005ab73d30 > > > > > > --- trap 0, rip = 0, rsp = 0, rbp = 0 --- > > > > > > Uptime: 17m20s > > > > > > Dumping 607 out of 12240 > > > > > > MB:..3%..11%..22%..32%..43%..51%..61%..72%..82%..93% > > > > > > > > > > > > __curthread () at /usr/src/sys/amd64/include/pcpu_aux.h:55 > > > > > > 55 /usr/src/sys/amd64/include/pcpu_aux.h: No such file > > > > > > or > > > > > > directory. > > > > > > (kgdb) bt > > > > > > #0 __curthread () at > > > > > > /usr/src/sys/amd64/include/pcpu_aux.h:55 > > > > > > #1 doadump (textdump=1) at ../../../kern/kern_shutdown.c:371 > > > > > > #2 0xffffffff80b83ada in kern_reboot (howto=260) > > > > > > at ../../../kern/kern_shutdown.c:451 > > > > > > #3 0xffffffff80b83f33 in vpanic (fmt=<optimized out>, > > > > > > ap=<optimized out>) > > > > > > at ../../../kern/kern_shutdown.c:880 > > > > > > #4 0xffffffff80b83d53 in panic (fmt=<unavailable>) > > > > > > at ../../../kern/kern_shutdown.c:807 > > > > > > #5 0xffffffff80be7152 in propagate_priority > > > > > > (td=0xfffff80196959740) > > > > > > at ../../../kern/subr_turnstile.c:228 > > > > > > #6 0xffffffff80be7d1c in turnstile_wait > > > > > > (ts=0xfffff8000357a780, > > > > > > owner=<optimized out>, queue=0) at > > > > > > ../../../kern/subr_turnstile.c:785 > > > > > > #7 0xffffffff80b62ca9 in __mtx_lock_sleep > > > > > > (c=0xfffff80003969bd0, > > > > > > v=<optimized out>) at ../../../kern/kern_mutex.c:654 > > > > > > #8 0xffffffff8086fcc0 in ppcintr (arg=0xfffff80003969b00) > > > > > > at ../../../dev/ppc/ppc.c:1546 > > > > > > #9 0xffffffff80b4637c in intr_event_execute_handlers > > > > > > (p=<optimized > > > > > > out>, > > > > > > ie=0xfffff800030d9d00) at ../../../kern/kern_intr.c:1143 > > > > > > #10 ithread_execute_handlers (p=<optimized out>, > > > > > > ie=0xfffff800030d9d00) > > > > > > at ../../../kern/kern_intr.c:1156 > > > > > > #11 ithread_loop (arg=0xfffff800039aa7e0) at > > > > > > ../../../kern/kern_intr.c:1236 > > > > > > #12 0xffffffff80b42e1e in fork_exit ( > > > > > > callout=0xffffffff80b46140 <ithread_loop>, > > > > > > arg=0xfffff800039aa7e0, > > > > > > frame=0xfffffe005ab73d40) at > > > > > > ../../../kern/kern_fork.c:1080 > > > > > > #13 <signal handler called> > > > > > > (kgdb) > > > > > > > > > > > > > > > > > > > > > --00000000000072604805caf2afba--
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