----- "Bob Montgomery" <bob.montgomery(a)hp.com> wrote:
I'm working on a dump of a system that did not have a PID 1. I
don't
think it's relevant to the crash itself, but it does cause crash get
a seg fault.
crash> ps | head
PID PPID CPU TASK ST %MEM VSZ RSS COMM
0 0 0 ffffffff805144c0 RU 0.0 0 0 [swapper]
0 -1 1 ffff81012bc0a100 RU 0.0 0 0 [swapper]
2 -1 0 ffff81012bd3c040 IN 0.0 0 0 [migration/0]
3 -1 0 ffff81012bd3e7c0 RU 0.0 0 0 [ksoftirqd/0]
4 -1 0 ffff81012bd3e080 IN 0.0 0 0 [watchdog/0]
5 -1 1 ffff81012bd3f800 IN 0.0 0 0 [migration/1]
6 -1 1 ffff81012bd3f0c0 RU 0.0 0 0 [ksoftirqd/1]
7 -1 1 ffff81012bc0a840 IN 0.0 0 0 [watchdog/1]
8 -1 0 ffff81012af02880 IN 0.0 0 0 [events/0]
crash> mount
Segmentation fault (core dumped)
In cmd_mount, this returns null and subsequent use causes the seg fault:
1156
1157 namespace_context = pid_to_context(1);
I don't know if it was important to have the context of pid 1 for
reporting mounts, or just any context, but this hack makes the problem
go away, although not a very efficient way to find the lowest existing
PID above 0.
Yeah, it's not important to use the context of pid 1, but it just needs
some context, and I had presumed that init would always exist. I thought
that the panic("Attempted to kill the idle task!") in do_exit() would
prevent pid 1 from ever going away -- but apparently your kernel figured
out how to do it elsewhere... ;-)
Your patch would pick a kernel thread pid, and apparently everything still
works OK? That being the case, it's fine with me.
Thanks,
Dave
--- filesys.c.orig 2010-08-18 14:03:26.000000000 -0600
+++ filesys.c 2010-08-18 14:10:02.000000000 -0600
@@ -1153,8 +1153,12 @@ cmd_mount(void)
ulong vfsmount = 0;
int flags = 0;
int save_next;
+ ulong pid;
- namespace_context = pid_to_context(1);
+ /* find a context */
+ pid = 1;
+ while ((namespace_context = pid_to_context(pid)) == NULL)
+ pid++;
while ((c = getopt(argcnt, args, "ifn:")) != EOF) {
switch(c)
Bob Montgomery
At HP
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