----- "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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