Re: [Crash-utility] crash CPU bound waiting for user response
D. Hugh Redelmeier wrote:
I am running crash in a shell window of JOVE. JOVE is an
EMACS-subset
editor.
crash isn't really happy. Here is an example:
crash> task
WARNING: terminal is not fully functional
- (press RETURN)
==> It does not say in what way the terminal is not fully functional. That seems like
a bug.
Sorry, but I have no idea where that WARNING message is coming from,
i.e., it's not coming from the crash/gdb code base, nor does the
string "functional" show up in any of the external libraries. There
is a crash function that prints "WARNING:" before a passed-in message,
but no instances of it issue that "functional" message. And the
"(press RETURN)" is most certainly not associated with the crash/gdb
code base.
So I don't know what the "It" is.
==> Worse: while it is awaiting my RETURN, it is burning 100% of the CPU!
Here is what "ps laxgwf" says about the crash process and its child.
F UID PID PPID PRI NI VSZ RSS WCHAN STAT TTY TIME COMMAND
4 0 4426 4406 25 0 416812 332764 - R+ pts/5 80:36 |
| \_ crash --readnow
/usr/lib/debug/lib/modules/2.6.21-1.3228.fc7/vmlinux /var/crash/2007-07-02-13:42/vmcore
0 0 4989 4426 18 0 73976 740 - S+ pts/5 0:00 |
| \_ /usr/bin/less -E -X -Ps -- MORE -- forward\: <SPACE>,
<ENTER> or j backward\: b or k quit\: q
strace of the crash process shows an infinite sequence of:
wait4(4989, 0x7fffcd9cae90, WNOHANG, NULL) = 0
wait4(4989, 0x7fffcd9cae90, WNOHANG, NULL) = 0
wait4(4989, 0x7fffcd9cae90, WNOHANG, NULL) = 0
wait4(4989, 0x7fffcd9cae90, WNOHANG, NULL) = 0
This is very wasteful.
There are other ways to get into this state. Other places less is
being used and is waiting. Probably wherever less is used even if it
isn't waiting.
I just tested: this problem exists when using a normal xterm.
Yeah, I have seen this on occasions, but I have never been able
to reproduce it on demand. There was a patch suggestion a while ago,
but I deferred it until I could reliably reproduce it for testing
before taking it in.
Dave