[PATCH] Bug in "sys_init_module", kernel/module.c, 2.4.19

[Kingsley Cheung]

Hi,

I've a trivial patch against kernel/module.c for 2.4.19 below that 
fixes a problem with the initialisation of a stack of modules.  
Though it rarely occurs, without this the kernel can crash when a module 
is being initialised and before this initialisation finishes another 
*dependent* module is loaded.  This occurs when the first module blocks 
in init_module and releases the big kernel lock.  I discussed this earlier 
with Keith Owens but it looks like its been forgotten:  

On Mon, 5 Aug 2002, Keith Owens wrote:

> On Mon, 5 Aug 2002 17:25:21 +1000 (EST),
> Kingsley Cheung <[e-mail]> wrote:
> >Anyway, at this point I'm still not certain I've completely grasped your
> >reply. Maybe I didn't make my first email clear.  If this is so, then
> >what I was saying is that the invocation of "init_module" functions of
> >*dependent* modules needs be appropriately serialised.  Right now
> >"sys_init_module" is relying on the big kernel lock to completely
> >serialise these calls but if any "init_module" function blocks, the
> >kernel lock is released and this serialisation can be broken.  Maybe one
> >way to avoid this is to check the flags of modules depended on during
> >"sys_init_module". So if the MOD_RUNNING flag is not set for the module
> >we depend on, then the module currently being loaded must have its
> >invocation of "sys_init_module" wait or return an appropriate error
> >indicating why.
>
> Agreed, this is a bigger problem than a failed module_init().  I am
> going to think about this overnight.
>

Cheers,
Kingsley

--- module.c.old        Wed Oct 16 10:46:10 2002
+++ module.c    Wed Oct 16 10:50:13 2002
@@ -528,6 +528,10 @@
                                "(no longer?) a module.\n");
                        goto err3;
                }
+
+               /* Dependents must be initialised and running */
+               if (!(d->flags & MOD_RUNNING) || (d->flags & MOD_DELETED))
+                       goto err3;
        }
 
        /* Update module references.  */