Re: Recent i386-GENERIC panic

[Paul Goyette <paul%whooppee.com@localhost>]

On Fri, 16 Sep 2011, John D. Baker wrote:

> On Fri, 16 Sep 2011, John D. Baker wrote:
>
> > if (mod->mod_required[i])
> >    printf("module %s requires module %s!\n",
> >        mod->mod_info->mi_name, mod->mod_required[i]->mod_info->mi_name);
> >
> > (It's just finished compiling.  Will try shortly.)
>
> First I noticed that the kernel size with the above added lines was
> EXACTLY the same as without it.

Very odd.

> Next, no message from the above printf was ever printed.  ...

Actually, I'm not surprised - see below ...

> ... I thought I
> might have stale objects around, so I deleted the compile/GENERIC directory 
> and $RELEASEDIR/binary/kernel/netbsd-GENERIC.gz file and
> compiled again.
>
> As before, resulting kernel size is the same as without the printf,
> no messages at all from it.
>
> When the panic occurs, the KASSERT() line number is 695, three lines
> down from stock, so the source was compiled.
>
> I take that to mean "mod->mod_required[i]" is NULL in the "if()", but is
> non-NULL in the KASSERT()!  Whisky Tango Foxtrot /IMI/ K

No, the KASSERT panics when mod->mod_required[i] _is_ NULL.

It might be more clear to use the following debug printf's:

Index: kern_module.c
===================================================================
RCS file: /cvsroot/src/sys/kern/kern_module.c,v
retrieving revision 1.81
diff -u -p -r1.81 kern_module.c
--- kern_module.c       14 Sep 2011 12:29:22 -0000      1.81
+++ kern_module.c       16 Sep 2011 14:59:01 -0000
@@ -684,14 +684,19 @@ module_enqueue(module_t *mod)
         * This is so that autounload can unload requisite modules with
         * only one pass through the queue.
         */
+       printf("%s required %d modules\n", mod->mod_info->mi_name,
+               mod->nrequired);
        if (mod->mod_nrequired) {
                TAILQ_INSERT_HEAD(&module_list, mod, mod_chain);

                /* Add references to the requisite modules. */
                for (i = 0; i < mod->mod_nrequired; i++) {
+                       printf("   %s",
+                               mod->mod_required[i]->mod_info->mi_name);
                        KASSERT(mod->mod_required[i] != NULL);
                        mod->mod_required[i]->mod_refcnt++;
                }
+               printf("\n");
        } else {
                TAILQ_INSERT_TAIL(&module_list, mod, mod_chain);
        }
@@ -772,6 +777,8 @@ module_do_builtin(const char *name, modu
                                return error;
                        }
                        mod->mod_required[mod->mod_nrequired++] = mod2;
+                       if (mod2 == NULL)
+                               printf("NULL require in %s\n", __func__);
                }
        }

@@ -1036,6 +1043,8 @@ module_do_load(const char *name, bool is
                        if (error != 0)
                                goto fail;
                        mod->mod_required[mod->mod_nrequired++] = mod2;
+                       if (mod2 == NULL)
+                               printf("NULL require in %s\n", __func__);
                }
        }


In addition to printing out the dependencies, it will hopefully tell us 
which call is returning NULL.

-------------------------------------------------------------------------
| Paul Goyette     | PGP Key fingerprint:     | E-mail addresses:       |
| Customer Service | FA29 0E3B 35AF E8AE 6651 | paul at whooppee.com    |
| Network Engineer | 0786 F758 55DE 53BA 7731 | pgoyette at juniper.net |
| Kernel Developer |                          | pgoyette at netbsd.org  |
-------------------------------------------------------------------------