Date: Fri, 30 Apr 2004 15:28:29 +0400 From: Dmitry Sivachenko <mitya@cavia.pp.ru> To: hackers@freebsd.org Subject: /bin/sh question Message-ID: <20040430112829.GA93243@sinbin.demos.su>
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Hello!
We use recent -STABLE.
We observed /bin/sh looping forever executing a script.
We run this script with -T option to sh(1).
When sh(1) receives a HUP, we entering our trap handler which spawns
child process. When this process exits, sh(1) loops.
The backtrace is the following:
(gdb) bt
#0 0x80763fc in wait4 ()
#1 0x8075941 in wait3 ()
#2 0x8051f8a in waitproc (block=1, status=0xbfbffa0c)
at /mnt/backup/releng_4/src/bin/sh/jobs.c:1025
#3 0x8051cbd in dowait (block=1, job=0x80c6000)
at /mnt/backup/releng_4/src/bin/sh/jobs.c:926
#4 0x8051b8a in waitforjob (jp=0x80c6000, origstatus=0xbfbffa88)
at /mnt/backup/releng_4/src/bin/sh/jobs.c:870
#5 0x804be33 in evalcommand (cmd=0x80b6d6c, flags=0, backcmd=0x0)
at /mnt/backup/releng_4/src/bin/sh/eval.c:904
#6 0x804acc0 in evaltree (n=0x80b6d6c, flags=0)
at /mnt/backup/releng_4/src/bin/sh/eval.c:281
#7 0x804aafa in evaltree (n=0x80b6e04, flags=0)
at /mnt/backup/releng_4/src/bin/sh/eval.c:199
#8 0x804aafa in evaltree (n=0x80b6e38, flags=0)
at /mnt/backup/releng_4/src/bin/sh/eval.c:199
#9 0x804aa73 in evalstring (
s=0x80c5100 "rm -f /tmp/st28742.box221.zecke.demos.su; _clean SIGHUP /dev/tt
yph.28742.zecke.demos.su 28742; exit")
at /mnt/backup/releng_4/src/bin/sh/eval.c:171
#10 0x80598da in dotrap () at /mnt/backup/releng_4/src/bin/sh/trap.c:401
#11 0x804acf6 in evaltree (n=0x80b6d00, flags=0)
at /mnt/backup/releng_4/src/bin/sh/eval.c:290
#12 0x80528f4 in cmdloop (top=1) at /mnt/backup/releng_4/src/bin/sh/main.c:250
The waitproc() at jobs.c:926 returns -1 and sets errno to ECHILD (because
the child does not exist at that time).
Since (pid <= 0) condition is true at jobs.c:935, -1 is returned and we are
entering dotrap() at jobs.c:870. dotrap() never alters (struct job *)state.
So we get an infinite loop around jobs.c:869.
Unfortunatelly I can't provide a simple enough how-to-observe script for
this, but the above logic seems weird for me. I can provide additional
details or coredump if needed.
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