tcsh hang on exit

Hi!

http://bsd.pw/scale_slides.pdf
p 28 recomends add to ~/.tcshrc:
set savehist = (99999999 merge lock)

I use this for a while, but some time ago found that after term close csh hangs.
Term close - close xfce4-terminal by X bytton. Exit in terminal - does not trigger issue.


Reproduce:
Add/set in ~/.cshrc: set savehist = (99999999 merge lock)
Open and close terminal with tsch shell.
Run top -aSCI -m io to ensure that csh writes to disk. (13+ only)
~/.history.lock exist, csh process continue running.


Truss show infinite loop:
...
78009: link("/home/rim/.rimwks.local.90dc6","/home/rim/.history.lock") ERR#17 'File exists'
78009: unlink("/home/rim/.rimwks.local.90dc6")	 = 0 (0x0)
78009: sigprocmask(SIG_SETMASK,{ },0x0)		 = 0 (0x0)
78009: nanosleep({ 0.100000000 })		 = 0 (0x0)
78009: sigprocmask(SIG_BLOCK,{ SIGHUP|SIGINT|SIGQUIT|SIGTERM|SIGTSTP|SIGCHLD|SIGTTIN|SIGTTOU },{ }) = 0 (0x0)
78009: __sysctl("kern.hostname",2,0x7fffffffb8a0,0x7fffffffb348,0x0,0) = 0 (0x0)
78009: getpid()					 = 78009 (0x130b9)
78009: openat(AT_FDCWD,"/home/rim/.rimwks.local.b5e4e",O_WRONLY|O_FSYNC|O_CREAT|O_TRUNC|O_EXCL,00) = 0 (0x0)
78009: close(0)					 = 0 (0x0)
78009: link("/home/rim/.rimwks.local.b5e4e","/home/rim/.history.lock") ERR#17 'File exists'
78009: unlink("/home/rim/.rimwks.local.b5e4e")	 = 0 (0x0)
78009: sigprocmask(SIG_SETMASK,{ },0x0)		 = 0 (0x0)
78009: nanosleep({ 0.100000000 })		 = 0 (0x0)
78009: sigprocmask(SIG_BLOCK,{ SIGHUP|SIGINT|SIGQUIT|SIGTERM|SIGTSTP|SIGCHLD|SIGTTIN|SIGTTOU },{ }) = 0 (0x0)
78009: __sysctl("kern.hostname",2,0x7fffffffb8a0,0x7fffffffb348,0x0,0) = 0 (0x0)
78009: getpid()					 = 78009 (0x130b9)
78009: openat(AT_FDCWD,"/home/rim/.rimwks.local.d0437",O_WRONLY|O_FSYNC|O_CREAT|O_TRUNC|O_EXCL,00) = 0 (0x0)
78009: close(0)					 = 0 (0x0)
78009: link("/home/rim/.rimwks.local.d0437","/home/rim/.history.lock") ERR#17 'File exists'
78009: unlink("/home/rim/.rimwks.local.d0437")	 = 0 (0x0)
78009: sigprocmask(SIG_SETMASK,{ },0x0)		 = 0 (0x0)
...


This stop only after I remove empty .history.lock or kill process.

Reprodused on 12.2 and 13. amd64.
On 13 it causes disk writes with ~2mb/sec per csh process, on 12.2 no disk writes.

I have try use "truss -fp PID" to understand what goes wrong, but every time I connect truss before
exit/term close - issue does not happen.

contrib/tcsh/dotlock.c - code looks simple, and I suspect that some race condition in kernel exist
that causes fail at this code:
	if (st.st_nlink != 2) {
then it run first time on process exit, in next time code fails on link - file already exist.
I try to reproduce this in small test app, by copy-paste code from contrib/tcsh/dotlock.c but
no errors happen and st_nlink == 2.

My second version that tcsh do something unusual with signal handling and truss revert it back.


1. Does some one expect same issue/can reproduse it?

2. I have mounted ".eli on /home/rim (ufs, local, noatime, nosuid, soft-updates)", is it OK that
FreeBSD 13 write/flush to often/on every file create/delete and FreeBSD 12.2 does not?

3. If I do not use lock option then no chs hang on exit, but if terminal closed without exit
file .history.1583640 (diff nums) created. Is any work around for this?