Several Misc SCSI updates...

Several Misc SCSI updates...

[Doug Ledford]

These bring the scsi subsys up to the new module loader semantics.  There 
is more work to be done on inter-module locking here, but we need to solve 
the whole module->live is 0 during init problem first or else it's a waste 
of time.

bk://linux-scsi.bkbits.net/scsi-dledford

ChangeSet@1.866, 2002-11-17 15:02:31-05:00, dledford@flossy.devel.redhat.com
  Merge bk://linux.bkbits.net/linux-2.5
  into flossy.devel.redhat.com:/usr/local/home/dledford/bk/linus-2.5

ChangeSet@1.810.1.5, 2002-11-16 21:31:05-05:00, dledford@aladin.rdu.redhat.com
  Christoph Hellwig posted a patch that conflicted with a lot of my own
  changes, so this is the merge of his work into my own.

ChangeSet@1.810.1.4, 2002-11-16 21:22:06-05:00, dledford@aladin.rdu.redhat.com
  aic7xxx_old: fix check_region/request_region usage so that the module
        may be loaded/unloaded/reloaded

ChangeSet@1.810.1.3, 2002-11-16 20:59:23-05:00, dledford@aladin.rdu.redhat.com
  Update high level scsi drivers to use struct list_head in templates
  Update scsi.c for struct list_head in upper layer templates
  Update scsi.c for new module loader semantics

ChangeSet@1.810.1.2, 2002-11-16 14:51:42-05:00, dledford@aladin.rdu.redhat.com
  scsi.c:
  - Comment out GET_USE_COUNT, it's a bogus test anyway
  - Don't panic on failure to allocate sg table slab slots, fail gracefully
  - init_scsi() leaks all sorts of crap on failed module load

ChangeSet@1.805.6.1, 2002-11-11 18:02:55-05:00, dledford@aladin.rdu.redhat.com
  mptscsih.h: compile fix


-- 
  Doug Ledford <dledford@redhat.com>     919-754-3700 x44233
         Red Hat, Inc. 
         1801 Varsity Dr.
         Raleigh, NC 27606
  

Re: Several Misc SCSI updates...

[Linus Torvalds]

On Sun, 17 Nov 2002, Doug Ledford wrote:
>
> These bring the scsi subsys up to the new module loader semantics.  There 
> is more work to be done on inter-module locking here, but we need to solve 
> the whole module->live is 0 during init problem first or else it's a waste 
> of time.

Hey, just remove the "live" test, I think it's over-eager and likely to 
just cause extra code to work around it rather than fix anything.

		Linus

Re: Several Misc SCSI updates...

[Doug Ledford]

On Sun, Nov 17, 2002 at 12:29:25PM -0800, Linus Torvalds wrote:
> 
> On Sun, 17 Nov 2002, Doug Ledford wrote:
> >
> > These bring the scsi subsys up to the new module loader semantics.  There 
> > is more work to be done on inter-module locking here, but we need to solve 
> > the whole module->live is 0 during init problem first or else it's a waste 
> > of time.
> 
> Hey, just remove the "live" test, I think it's over-eager and likely to 
> just cause extra code to work around it rather than fix anything.

Won't work.  module->live is what Rusty uses to indicate that the module 
is in the process of unloading, which is when we *do* want the attempt to 
module_get() to fail.  I think the process out to basically be:

load module into mem
set module->live = 1
call module_init
export module syms
done loading module

on module exit:
unexport module syms
set module->live 0
call module_exit
free module memory
done unloading.

That *should* solve all the races Rusty is trying to solve without the 
problems we've had so far, but this is only after a few minutes of 
thinking....

-- 
  Doug Ledford <dledford@redhat.com>     919-754-3700 x44233
         Red Hat, Inc. 
         1801 Varsity Dr.
         Raleigh, NC 27606
  

Re: Several Misc SCSI updates...

[Linus Torvalds]

On Sun, 17 Nov 2002, Doug Ledford wrote:
> 
> Won't work.  module->live is what Rusty uses to indicate that the module 
> is in the process of unloading, which is when we *do* want the attempt to 
> module_get() to fail.

That's fine, as long as "module_get()" is the only thing that cares. Just 
make it go "live" early as you indicate, and everybody should be happy. I 
certainly agree that it should be illegal to do more module_get()'s once 
we've already started unloading..

		Linus

Re: Several Misc SCSI updates...

[Alexander Viro]

On Sun, 17 Nov 2002, Linus Torvalds wrote:

> 
> On Sun, 17 Nov 2002, Doug Ledford wrote:
> > 
> > Won't work.  module->live is what Rusty uses to indicate that the module 
> > is in the process of unloading, which is when we *do* want the attempt to 
> > module_get() to fail.
> 
> That's fine, as long as "module_get()" is the only thing that cares. Just 
> make it go "live" early as you indicate, and everybody should be happy. I 
> certainly agree that it should be illegal to do more module_get()'s once 
> we've already started unloading..

On the unload side it's OK.  module_get() also breaks during _init_ and that's
the problem.  IOW, you'll need to make every block device driver to set ->live
manually.  Smells like a wrong API...

Re: Several Misc SCSI updates...

[Doug Ledford]

On Sun, Nov 17, 2002 at 04:55:26PM -0500, Alexander Viro wrote:
> 
> 
> On Sun, 17 Nov 2002, Linus Torvalds wrote:
> 
> > 
> > On Sun, 17 Nov 2002, Doug Ledford wrote:
> > > 
> > > Won't work.  module->live is what Rusty uses to indicate that the module 
> > > is in the process of unloading, which is when we *do* want the attempt to 
> > > module_get() to fail.
> > 
> > That's fine, as long as "module_get()" is the only thing that cares. Just 
> > make it go "live" early as you indicate, and everybody should be happy. I 
> > certainly agree that it should be illegal to do more module_get()'s once 
> > we've already started unloading..
> 
> On the unload side it's OK.  module_get() also breaks during _init_ and that's
> the problem.  IOW, you'll need to make every block device driver to set ->live
> manually.  Smells like a wrong API...

This is the patch I just put into my tree (beware cut-n-paste breakage is 
in effect, but Linus should have the change in his tree momentarily 
anyway):

diff -Nru a/kernel/module.c b/kernel/module.c
--- a/kernel/module.c   Sun Nov 17 17:02:48 2002
+++ b/kernel/module.c   Sun Nov 17 17:02:48 2002
@@ -1058,6 +1058,15 @@
        list_add(&mod->extable.list, &extables);
        spin_unlock_irq(&modlist_lock);

+       /* Note, setting the mod->live to 1 here is safe because we haven't
+        * linked the module into the system's kernel symbol table yet,
+        * which means that the only way any other kernel code can call
+        * into this module right now is if this module hands out entry
+        * pointers to the other code.  We assume that no module hands out
+        * entry pointers to the rest of the kernel unless it is ready to
+        * have them used.
+        */
+       mod->live = 1;
        /* Start the module */
        ret = mod->init ? mod->init() : 0;
        if (ret < 0) {
@@ -1070,9 +1079,10 @@
                        /* Mark it "live" so that they can force
                           deletion later, and we don't keep getting
                           woken on every decrement. */
-                       mod->live = 1;
-               } else
+               } else {
+                       mod->live = 0;
                        free_module(mod);
+               }
                up(&module_mutex);
                return ret;
        }
@@ -1087,7 +1097,6 @@
        mod->module_init = NULL;

        /* All ok! */
-       mod->live = 1;
        up(&module_mutex);
        return 0;
 }


-- 
  Doug Ledford <dledford@redhat.com>     919-754-3700 x44233
         Red Hat, Inc. 
         1801 Varsity Dr.
         Raleigh, NC 27606