[Crash-utility] mount cmd crashes crash

[Dave Anderson]

----- "Bob Montgomery" <bob.montgomery at 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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