Re: panic: mtx_lock_spin: recursed on non-recursive mutex vtbuf @ ..

On Tue, Jun 2, 2026 at 3:01 PM Aleksandr Rybalko <ray@freebsd.org> wrote:
>
> Hey, Adrian!
>
> Know why, but working on a fix yet.
>
> Thanks!
>
> вт, 2 черв. 2026 р. о 20:01 Adrian Chadd <adrian@freebsd.org> пише:
>>
>> hey! was this eventually fixed? I just hit it, notably a few days old
>> -head (i think), but I still hit it.
>>
>> THanks!
>>
>>
>> -a
>>
>> On Fri, 22 May 2026 at 08:51, Aleksandr Rybalko <ray@freebsd.org> wrote:
>> >
>> > Hey guys!
>> >
>> > Yeah, it seems my.
>> > I will look into it today.
>> >
>> > Thanks!
>> >
>> > пт, 22 трав. 2026 р. о 18:35 Ryan Libby <rlibby@freebsd.org> пише:
>> >>
>> >> On Fri, May 22, 2026 at 1:46 AM Bjoern A. Zeeb
>> >> <bzeeb-lists@lists.zabbadoz.net> wrote:
>> >> >
>> >> > Hi,
>> >> >
>> >> > I was using the mouse in tmux on v1 when everying stopped.
>> >> > Sadly we didn't switch to v0 for console but it seems I managed to get a dump only checking now; the kernel from then is already gone.
>> >> >
>> >> > core.txt said.
>> >> >
>> >> > panic: mtx_lock_spin: recursed on non-recursive mutex vtbuf @ /usr/home/test/Sources/git/FreeBSD/freebsd-src.git/sys/dev/vt/vt_buf.c:744
>> >> >
>> >> > cpuid = 1
>> >> > time = 1779437567
>> >> > KDB: stack backtrace:
>> >> > db_trace_self_wrapper() at db_trace_self_wrapper+0x2b/frame 0xfffffe00d773e7a0
>> >> > vpanic() at vpanic+0x149/frame 0xfffffe00d773e8d0
>> >> > panic() at panic+0x43/frame 0xfffffe00d773e930
>> >> > __mtx_lock_spin_flags() at __mtx_lock_spin_flags+0x11b/frame 0xfffffe00d773e970
>> >> > vtbuf_flush_mark() at vtbuf_flush_mark+0x82/frame 0xfffffe00d773e9b0
>> >> > vtbuf_unmark_on_cross() at vtbuf_unmark_on_cross+0xcc/frame 0xfffffe00d773e9d0
>> >> > vtterm_fill() at vtterm_fill+0x27/frame 0xfffffe00d773ea00
>> >> > teken_subr_erase_line() at teken_subr_erase_line+0x90/frame 0xfffffe00d773ea20
>> >> > teken_state_2() at teken_state_2+0x497/frame 0xfffffe00d773ea40
>> >> > teken_input_char() at teken_input_char+0x47/frame 0xfffffe00d773ea60
>> >> > teken_input() at teken_input+0x9f/frame 0xfffffe00d773ea90
>> >> > termtty_outwakeup() at termtty_outwakeup+0xcf/frame 0xfffffe00d773eb60
>> >> > ttydisc_write() at ttydisc_write+0x337/frame 0xfffffe00d773ecd0
>> >> > ttydev_write() at ttydev_write+0x13f/frame 0xfffffe00d773ed10
>> >> > devfs_write_f() at devfs_write_f+0xf3/frame 0xfffffe00d773ed70
>> >> > dofilewrite() at dofilewrite+0x81/frame 0xfffffe00d773edc0
>> >> > sys_writev() at sys_writev+0x69/frame 0xfffffe00d773ee00
>> >> > amd64_syscall() at amd64_syscall+0x168/frame 0xfffffe00d773ef30
>> >> > fast_syscall_common() at fast_syscall_common+0xf8/frame 0xfffffe00d773ef30
>> >> > --- syscall (121, FreeBSD ELF64, writev), rip = 0x82601d5aa, rsp = 0x8207a3408, rbp = 0x8207a3430 ---
>> >> > KDB: enter: panic
>> >> >
>> >> >
>> >> > In case it helps, I believe this is file:line as reported by gdb in core.txt:
>> >> >
>> >> >      at /usr/home/test/Sources/git/FreeBSD/freebsd-src.git/sys/kern/kern_mutex.c:353
>> >> >      at /usr/home/test/Sources/git/FreeBSD/freebsd-src.git/sys/dev/vt/vt_buf.c:744
>> >> >      at /usr/home/test/Sources/git/FreeBSD/freebsd-src.git/sys/dev/vt/vt_buf.c:864
>> >> >      at /usr/home/test/Sources/git/FreeBSD/freebsd-src.git/sys/dev/vt/vt_buf.c:210
>> >> >      at /usr/home/test/Sources/git/FreeBSD/freebsd-src.git/sys/dev/vt/vt_buf.c:232
>> >> >      at /usr/home/test/Sources/git/FreeBSD/freebsd-src.git/sys/dev/vt/vt_core.c:1201
>> >> >      at /usr/home/test/Sources/git/FreeBSD/freebsd-src.git/sys/teken/teken.c:121
>> >> >      at /usr/home/test/Sources/git/FreeBSD/freebsd-src.git/sys/teken/teken_subr.h:558
>> >> >      at /usr/home/test/Sources/git/FreeBSD/freebsd-src.git/sys/teken/teken.c:255
>> >> >      at /usr/home/test/Sources/git/FreeBSD/freebsd-src.git/sys/teken/teken.c:284
>> >> >      at /usr/home/test/Sources/git/FreeBSD/freebsd-src.git/sys/teken/teken.c:317
>> >> >      at /usr/home/test/Sources/git/FreeBSD/freebsd-src.git/sys/kern/subr_terminal.c:422
>> >> >      at /usr/home/test/Sources/git/FreeBSD/freebsd-src.git/sys/sys/ttydevsw.h:114
>> >> >      at /usr/home/test/Sources/git/FreeBSD/freebsd-src.git/sys/kern/tty_ttydisc.c:658
>> >> >      at /usr/home/test/Sources/git/FreeBSD/freebsd-src.git/sys/kern/tty.c:550
>> >> >      at /usr/home/test/Sources/git/FreeBSD/freebsd-src.git/sys/fs/devfs/devfs_vnops.c:1980
>> >> >      at /usr/home/test/Sources/git/FreeBSD/freebsd-src.git/sys/sys/file.h:372
>> >> >      at /usr/home/test/Sources/git/FreeBSD/freebsd-src.git/sys/kern/sys_generic.c:565
>> >> >      at /usr/home/test/Sources/git/FreeBSD/freebsd-src.git/sys/kern/sys_generic.c:492
>> >> >      at /usr/home/test/Sources/git/FreeBSD/freebsd-src.git/sys/kern/sys_generic.c:478
>> >> >      at /usr/home/test/Sources/git/FreeBSD/freebsd-src.git/sys/amd64/amd64/../../kern/subr_syscall.c:193
>> >> >
>> >> >
>> >> > --
>> >> > Bjoern A. Zeeb                                                     r15:7
>> >> >
>> >>
>> >> I think it's probably related to or a regression from
>> >> 8db0553ed6d8 ("vt: Clear cut-paste selection if the area intersects
>> >> with the filled region")
>> >> https://cgit.freebsd.org/src/commit/?id=8db0553ed6d8636d82a26896237099526b93be19
>> >>
>> >> which added vtbuf_unmark_on_cross() which is in your panic stack.
>> >>
>> >> I don't know this code but it looks like the mutex is first taken by
>> >> teken_input / teken_funcs_pre_input / vtterm_pre_input and then again
>> >> by teken_input with your panic stack.
>> >>
>> >> Ryan

How is the locking supposed to work in vt_mouse_event anyway?

Unsolicited suggestion: require that the vb_lock be held on entry to
vtbuf_set_mark, remove the lock acquisition from vtbuf_flush_mark, and
make the call path through vt_mouse_event to vtbuf_set_mark and
vtbuf_unmark acquire the lock.

Ryan