Module Refcount & Stuff mini-FAQ

Module Refcount & Stuff mini-FAQ

[Rusty Russell]

[ Suggestions welcome ]

Golden Rule: If you are calling though a function pointer into a
(different) module, you must hold a reference to that module.
Otherwise you risk sleeping in the module while it is unloaded.

Q: How do I get a reference to a module?
A: Usually, a successful call to try_module_get(owner).  You don't
   need to check for owner != NULL, BTW.

Q: When does try_module_get(owner) fail?
A: When the module is not ready to be entered (ie. still in
   init_module) or it is being removed.  It fails to prevent you
   entering the module as it is being discarded (init might fail, or
   it's being removed).

Q: But modules call my register() routine which wants to call back
   into one of the function pointers immediately, and so
   try_module_get() fails!
A: You're being called from the module, so someone already has a
   reference (unless there's a bug), so you don't need a
   try_module_get().

   This does mean that if you were to register a structure for
   *another* module (does anyone do this?) you'd need to have a
   reference to it.

Q: How do I put the reference back?
A: Using module_put(owner) (owner == NULL is OK).

Q: Do I really need to put try_module_get() before every function ptr
   call?
A: If the function does not sleep (any cannot be preempted) ie. is
   called in softirq or hardirq context, you can omit this step, since
   you obviously won't sleep inside the module.

   Also, most structs have clear "start" and "stop" functions
   (eg. mount/umount), so you only need one try_module_get()
   on start, and module_put() on stop.

Q: Is it safe to call try_module_get() and module_put() from an
   interrtupt / softirq?
A: Yes.

Q: My code use "MOD_INC_USE_COUNT".  Do I still need to adjust my
   module count when someone calls one of my functions?
A: No, you never need to adjust your own module count.  There are five
   ways a function in your module can get called: firstly, it could be
   your module_init() function, in which case the module code holds a
   reference.  It could be another module using one of your
   EXPORT_SYMBOL'ed functions, in which case you cannot be removed
   since they would have to be removed first.  It could be a module
   which found an EXPORT_SYMBOL'ed function using symbol_get(), in
   which case they hold a reference count.  It could be through a
   function pointer which your module gave out previously, which is
   discussed above.  Finally, it could be from within your own module,
   in which case someone must already hold a reference.

Q: My code uses "__MOD_INC_USE_COUNT(reg->owner)", but now I get a
   warning at runtime that it is unsafe.  What do I need to do?
A: You need to use try_module_get(), and not call into the module if
   it fails (act as if it hasn't registered yet).  Note that you no
   longer need to check for NULL yourself, try_module_get() does that.

Q: My code used "GET_USE_COUNT(module)" to get the reference count.
A: Don't do that.  If module unloading is disabled, there is no
   reference count, and there is never a single value you can assign
   to.

Q: My code used "try_inc_mod_count(module)" to get the reference
   count.  Should I change it?
A: No hurry.  try_module_get() is exactly the same: the new name
   reflects that this is now the only way to get a reference.

Q: How does the code in try_module_get() work?
A: It disables preemption for a moment, checks the live flag, and then
   increments a per-cpu counter if the module is live.  This is even
   lighter-weight (in icache and cycles) than using a brlock, but has
   the same effect.  If CONFIG_MODULE_UNLOAD=n, it just becomes a
   check that the module is live.

Q: How does the module remove code work?
A: It stops the machine by scheduling threads for every other CPU,
   then they all disable interrupts.  At this stage we know that noone
   is in try_module_get(), so we can reliably read the counter.  If
   zero, or the rmmod user specified --wait, we set the live flag to
   false.  After this, the reference count should not increase, and
   each module_put() will wake us up, so we can check the counter
   again.

Q: Are these changes all so you could implement an in-kernel module
   linker?
A: No, they were to prevent load and unload races without altering
   every module, nor introducing drastic new requirements.

Q: Doesn't putting linking code into the kernel just add bloat?
A: The total linking code is about 200 generic lines, 100
   x86-specific lines.  The ia64 linking code is about 500 lines (it's
   the most complex).  Richard Henderson has a great suggestion for
   simplifying it furthur, which I'm implementing now.  "insmod" is
   now a single portable system call, meaning insmod can be written in
   about 20 lines of code.

   The previous code required to implement the two module loading
   system call, the module querying system call, and the /proc/ksyms
   output, required a little more code than the current x86 linker.

Q: Why not just fix the old code?
A: Because having something so intimate with the kernel in userspace
   greatly restricts what changes the kernel can make.  Moving into
   the kernel means I have implemented modversions, typesafe
   extensible module parameters and kallsyms without altering
   userspace in any way.  Future extensions won't have to worry about
   the modversions problem.

Q: Why not implement two-stage insert / two-stage delete?
A: Because I implemented it first and it sucked.  And because this
   *is* two-stage insert and two-stage delete, without exposing it to
   the modules using it, with the added advantage that the second
   stage is atomic (activation/deactivation is simply changing
   mod->live, modulo locking implementation magic detailed above).
   This prevents the race between deactivating the module and finding
   that someone has starting using it as you are deactivating it.

Hope that helps?
Rusty.
--
  Anyone who quotes me in their sig is an idiot. -- Rusty Russell.

Re: Module Refcount & Stuff mini-FAQ

[Werner Almesberger]

Rusty Russell wrote:
> Q: When does try_module_get(owner) fail?
> A: When the module is not ready to be entered (ie. still in
>    init_module) or it is being removed.  It fails to prevent you
>    entering the module as it is being discarded (init might fail, or
>    it's being removed).

I'd suggest "It fails in order to [...]" to avoid the "does work
exactly NOT as advertised" ambiguity ;-)

> Q: But modules call my register() routine which wants to call back
>    into one of the function pointers immediately, and so
>    try_module_get() fails!
> A: You're being called from the module, so someone already has a
>    reference (unless there's a bug), so you don't need a
>    try_module_get().

Hmm, I haven't really looked at your new code, but this sounds as
if try_module_get gets an exclusive lock. Is this true ? Doesn't
seem to make sense to me.

> Hope that helps?

Don't you want to repeat the golden rule at the end, just as a
polite reminder ? :-) (Just kidding.)

- Werner

-- 
  _________________________________________________________________________
 / Werner Almesberger, Buenos Aires, Argentina         wa@almesberger.net /
/_http://www.almesberger.net/____________________________________________/

Re: Module Refcount & Stuff mini-FAQ

[Rusty Russell]

In message <20021118233047.P1407@almesberger.net> you write:
> Rusty Russell wrote:
> > Q: When does try_module_get(owner) fail?
> > A: When the module is not ready to be entered (ie. still in
> >    init_module) or it is being removed.  It fails to prevent you
> >    entering the module as it is being discarded (init might fail, or
> >    it's being removed).
> 
> I'd suggest "It fails in order to [...]" to avoid the "does work
> exactly NOT as advertised" ambiguity ;-)

Ah, thanks, good catch.  I changed it to "This prevents you".

> > Q: But modules call my register() routine which wants to call back
> >    into one of the function pointers immediately, and so
> >    try_module_get() fails!
> > A: You're being called from the module, so someone already has a
> >    reference (unless there's a bug), so you don't need a
> >    try_module_get().
> 
> Hmm, I haven't really looked at your new code, but this sounds as
> if try_module_get gets an exclusive lock. Is this true ? Doesn't
> seem to make sense to me.

No, it doesn't.  The question is badly phrased.  How about:

Q: But the modules' init routine calls my register() routine which
   wants to call back into one of the function pointers immediately,
   and so try_module_get() fails! (because the module is not finished
   initializing yet)
A: You're being called from the module, so someone already has a
   reference (unless there's a bug), so you don't need a
   try_module_get().

   This does mean that if you were to register a structure for
   *another* module (does anyone do this?) you'd need to have a
   reference to it.

> > Hope that helps?
> 
> Don't you want to repeat the golden rule at the end, just as a
> polite reminder ? :-) (Just kidding.)

Heh.

Well, if we continue to start modules unisolated, I need to rewrite
the FAQ anyway...

Thanks,
Rusty.
--
  Anyone who quotes me in their sig is an idiot. -- Rusty Russell.

Re: Module Refcount & Stuff mini-FAQ

[Werner Almesberger]

Rusty Russell wrote:
> Q: But the modules' init routine calls my register() routine which
>    wants to call back into one of the function pointers immediately,
>    and so try_module_get() fails! (because the module is not finished
>    initializing yet)
> A: You're being called from the module, so someone already has a
>    reference (unless there's a bug), so you don't need a
>    try_module_get().

Hmm, I wouldn't call this the answer. How about:
 - Q: why does it fail ?
 - A: because you're initializing
 - solution: but since you're calling from a module, and the call
   goes back to the same module, you don't have to worry

This raises the question: why is this a special case ? The
registration function shouldn't have to know all these details.
(That's the whole point of try_module_get, isn't it ?)

Wouldn't it be possible to simply allow try_module_get also
while the module is initializing ?

> Well, if we continue to start modules unisolated, I need to rewrite
> the FAQ anyway...

Does "unisolated" mean that try_module_get would work ? If yes,
you've already solved the problem ;-)

- Werner

-- 
  _________________________________________________________________________
 / Werner Almesberger, Buenos Aires, Argentina         wa@almesberger.net /
/_http://www.almesberger.net/____________________________________________/

Re: Module Refcount & Stuff mini-FAQ

[Rusty Russell]

In message <20021124230758.A1549@almesberger.net> you write:
> Rusty Russell wrote:
> > Q: But the modules' init routine calls my register() routine which
> >    wants to call back into one of the function pointers immediately,
> >    and so try_module_get() fails! (because the module is not finished
> >    initializing yet)
> > A: You're being called from the module, so someone already has a
> >    reference (unless there's a bug), so you don't need a
> >    try_module_get().
> 
> Hmm, I wouldn't call this the answer. How about:
>  - Q: why does it fail ?
>  - A: because you're initializing
>  - solution: but since you're calling from a module, and the call
>    goes back to the same module, you don't have to worry
> 
> This raises the question: why is this a special case ? The
> registration function shouldn't have to know all these details.
> (That's the whole point of try_module_get, isn't it ?)

Yes, this is a fairly rare case: I'm debating it now.  For example,
scsi calls back into the module which just registered, as does the
block layer (to probe for partitions).

> > Well, if we continue to start modules unisolated, I need to rewrite
> > the FAQ anyway...
> 
> Does "unisolated" mean that try_module_get would work ? If yes,
> you've already solved the problem ;-)

At the cost of exposing the module to initialization races.

Rusty.
--
  Anyone who quotes me in their sig is an idiot. -- Rusty Russell.

Re: Module Refcount & Stuff mini-FAQ

[Werner Almesberger]

Rusty Russell wrote:
> At the cost of exposing the module to initialization races.

Hmm, what races are there that don't correspond to a bug in
some module ?

- Werner

-- 
  _________________________________________________________________________
 / Werner Almesberger, Buenos Aires, Argentina         wa@almesberger.net /
/_http://www.almesberger.net/____________________________________________/

Re: Module Refcount & Stuff mini-FAQ

[Rusty Russell]

In message <20021125033906.B1549@almesberger.net> you write:
> Rusty Russell wrote:
> > At the cost of exposing the module to initialization races.
> 
> Hmm, what races are there that don't correspond to a bug in
> some module ?

Ah, see other thread (weren't you at the kernel summit?).  There's
currently no way to abort if you've exposed interfaces and then
something fails ("don't do that" is great except noone knows that, and
it's not always possible or nice)

The old module code used to just ignore it.  My code tries to catch it
and leaves the module stuck (except if !CONFIG_MODULE_UNLOAD, in which
case it can't really detect it).

Since we have a way of isolating modules for the symmetric race on
exit, it makes sense to use it on entry (of course, try_inc_mod_count
would have to keep violating the rule during the transition).

Hope that helps,
Rusty.
--
  Anyone who quotes me in their sig is an idiot. -- Rusty Russell.

Re: Module Refcount & Stuff mini-FAQ

[Werner Almesberger]

Rusty Russell wrote:
> Ah, see other thread

Argh, there are only about a hundred threads on modules ;-)

> (weren't you at the kernel summit?).

Yes, but I hadn't paid much attention to modules before, so I only
understood about half of what you said, sorry. It was interesting
to learn that there were actually so many problems, though :-)

> There's currently no way to abort if you've exposed interfaces and then
> something fails ("don't do that" is great except noone knows that, and
> it's not always possible or nice)

Hmm, if "expose interface" == "publish symbol", why can't you simply
defer publishing until after initialization completes ? If "expose
interface" == "register something somewhere", then this has to be
undone anyway. Or am I overlooking something here ?

Thanks,
- Werner

-- 
  _________________________________________________________________________
 / Werner Almesberger, Buenos Aires, Argentina         wa@almesberger.net /
/_http://www.almesberger.net/____________________________________________/

Re: Module Refcount & Stuff mini-FAQ

[Rusty Russell]

In message <20021125232610.A22825@almesberger.net> you write:
> Rusty Russell wrote:
> > There's currently no way to abort if you've exposed interfaces and then
> > something fails ("don't do that" is great except noone knows that, and
> > it's not always possible or nice)
> 
> Hmm, if "expose interface" == "publish symbol", why can't you simply
> defer publishing until after initialization completes ? If "expose
> interface" == "register something somewhere", then this has to be
> undone anyway. Or am I overlooking something here ?

Yes, but between doing and undoing (in the failure path) someone has
started using the module.  The old modutils would unload it underneath
them here.  I catch it (if CONFIG_MODULE_UNLOAD, otherwise I can't)
and yell "module is now stuck" and leave it hanging.

Given we have a method of isolating a module already, it seems logical
to use it to prevent exactly this race.  Unfortunately my last attempt
assumed noone did this, and broke IDE and SCSI (hence pissing
*everyone* off 8).

Cheers,
Rusty.
--
  Anyone who quotes me in their sig is an idiot. -- Rusty Russell.

Re: Module Refcount & Stuff mini-FAQ

[Werner Almesberger]

Rusty Russell wrote:
> Yes, but between doing and undoing (in the failure path) someone has
> started using the module.

But how ? Don't we have only two ways of calling a module, i.e.
by symbol, or by callback ? All callbacks that might call a module
must be protected with try_module_get, right ? (*)

(*) Actually, if the registration can be revoked, and the
    deregistration function does properly synchronize with on-going
    callbacks, you shouldn't need try_module_get either. E.g.
    del_timer_sync doesn't need to know about module owners.

So, if you make try_module_get work during initialization, and
modules don't publish their symbols before initialization is done,
there should be no problem ?

> Given we have a method of isolating a module already, it seems logical
> to use it to prevent exactly this race.

But that's mainly the symbol-unload race, considering that any call
through a function pointer requires try_module_get anyway. Without
try_module_get, there would also be callback-unload races if
callback de-registration doesn't synchronize (e.g. del_timer
vs. del_timer_sync).

By the way, it's also not so nice that there can't be
callbacks at removal, e.g.

service_unregister(...)
{
	...
	for_pending_requests(req) {
		...
		if (try_module_get(req->owner))
			req->fn(req,REQUEST_CANCELLED);
		else
			printk(KERN_CRIT "we just dropped a request on the "
			  "floor, how nice\n");
		...
	}
	...
}

Calling this from the module removal function would be
perfectly safe.

Actually ... can't you allow modules to be called until the
cleanup function has returned ?

> Unfortunately my last attempt
> assumed noone did this, and broke IDE and SCSI (hence pissing
> *everyone* off 8).

Two in one strike ain't bad ;-) Maybe we can find something that
gets rid of that pesky NFS, too, e.g. by adding

#define while if    /* enforce efficient programming practices */

to linux/kernel.h, or such ;-)

- Werner

-- 
  _________________________________________________________________________
 / Werner Almesberger, Buenos Aires, Argentina         wa@almesberger.net /
/_http://www.almesberger.net/____________________________________________/

Re: Module Refcount & Stuff mini-FAQ

[Rusty Russell]

In message <20021126041212.B22825@almesberger.net> you write:
> Rusty Russell wrote:
> > Yes, but between doing and undoing (in the failure path) someone has
> > started using the module.
> 
> But how ? Don't we have only two ways of calling a module, i.e.
> by symbol, or by callback ? All callbacks that might call a module
> must be protected with try_module_get, right ? (*)

try_module_get() will succeed now during initialization, because the
module starts live.

> 
> (*) Actually, if the registration can be revoked, and the
>     deregistration function does properly synchronize with on-going
>     callbacks, you shouldn't need try_module_get either. E.g.
>     del_timer_sync doesn't need to know about module owners.

del_timer_sync is actually an oddity: most deregistration functions do
not block pending outstanding calls, they reference count and "unhook"
at deregistration, and delete when the refcount hits zero (if they do
anything at all 8).

(Note also: timers don't need to do try_module_get() since they can't
sleep).

> So, if you make try_module_get work during initialization, and
> modules don't publish their symbols before initialization is done,
> there should be no problem ?

Yes, but that's not the way things work currently: the interfaces to
reserve and publish are not separated.  And whether it's worth
separating them simply because of this, is the question.

> By the way, it's also not so nice that there can't be
> callbacks at removal, e.g.
> 
> service_unregister(...)
> {
> 	...
> 	for_pending_requests(req) {
> 		...
> 		if (try_module_get(req->owner))
> 			req->fn(req,REQUEST_CANCELLED);
> 		else
> 			printk(KERN_CRIT "we just dropped a request on the "
> 			  "floor, how nice\n");
> 		...
> 	}
> 	...
> }
> 
> Calling this from the module removal function would be
> perfectly safe.

Yes, and it's already in the list of exceptions: you're being called
by the module itself here.

Also, you're assuming that the coder chose not to do the
try_module_get() at request submission time.

Finally, there are some cases where a module can miss events while
unloading, but that's OK, because it's *guaranteed* to exit at this
point, so it must clean everything up in its cleanup routine anyway.
I couldn't think of an exception, can you?

> Actually ... can't you allow modules to be called until the
> cleanup function has returned ?

Only by splitting cleanup into "cleanup" and "destroy" (either by
having cleanup say "OK, I'm not live anymore" halfway though, or
having separate hooks).

We have over 1500 modules: not changing the interfaces to them was one
of the key goals.  If someone decides to later, fine.

> Two in one strike ain't bad ;-) Maybe we can find something that
> gets rid of that pesky NFS, too, e.g. by adding
> 
> #define while if    /* enforce efficient programming practices */
> 
> to linux/kernel.h, or such ;-)

Heh...  <sigh> Point taken.  I already decided to leave this one for
the moment, and do something more productive.

Thanks,
Rusty.
--
  Anyone who quotes me in their sig is an idiot. -- Rusty Russell.

Re: Module Refcount & Stuff mini-FAQ

[John Levon]

On Tue, Nov 19, 2002 at 09:58:56AM +1100, Rusty Russell wrote:

>    The previous code required to implement the two module loading
>    system call, the module querying system call, and the /proc/ksyms
>    output, required a little more code than the current x86 linker.

This makes it sound like you're not bringing /proc/ksyms back (or an
equivalent to let userspace know where modules are loaded). I hope this
isn't the case...

regards
john

-- 
Khendon's Law: If the same point is made twice by the same person,
the thread is over.

Re: Module Refcount & Stuff mini-FAQ

[Rusty Russell]

In message <20021119024032.GA99837@compsoc.man.ac.uk> you write:
> On Tue, Nov 19, 2002 at 09:58:56AM +1100, Rusty Russell wrote:
> 
> >    The previous code required to implement the two module loading
> >    system call, the module querying system call, and the /proc/ksyms
> >    output, required a little more code than the current x86 linker.
> 
> This makes it sound like you're not bringing /proc/ksyms back (or an
> equivalent to let userspace know where modules are loaded). I hope this
> isn't the case...

I implemented the minimal subset: it's trivial to put back.  The
important question is why do you want it?  Do you only want it when
CONFIG_MODULES=y?  Do you only want the exported symbols, or all
symbols?

If this is for oprofile to figure out where modules are, then an entry
in /proc/modules seems more appropriate, yes?

Rusty.
--
  Anyone who quotes me in their sig is an idiot. -- Rusty Russell.

Re: Module Refcount & Stuff mini-FAQ

[John Levon]

On Mon, Nov 25, 2002 at 10:02:00AM +1100, Rusty Russell wrote:

> I implemented the minimal subset: it's trivial to put back.  The
> important question is why do you want it?  Do you only want it when
> CONFIG_MODULES=y?  Do you only want the exported symbols, or all
> symbols?
> 
> If this is for oprofile to figure out where modules are, then an entry
> in /proc/modules seems more appropriate, yes?

Keith Owens pointed out that I need info on where each section is
mapped (consider the separate alloc of init/core sections; sure,
module_init() is an odd thing to profile but it's nice not to lose
samples). I don't care about the symbols themselves, but I believe Keith
does.

regards
john
-- 
Khendon's Law: If the same point is made twice by the same person,
the thread is over.

kksymoops

[Jeff Garzik]

Rusty,

What is the status of kksymoops?

I realize that you have a full plate, but [for the short time it existed 
in mainline] this was a incredibly useful feature for end users 
providing bug reports to me (and others).

I'm _not_ asking "when", just wondering what the plan is to resuscitate 
kksymoops.

	Jeff

Re: kksymoops

[Rusty Russell]

In message <3DD9AB88.4000102@pobox.com> you write:
> I'm _not_ asking "when", just wondering what the plan is to resuscitate 
> kksymoops.

Looks like someone pushed my patch.  Erm, OK, wonder if it works on
x86? 8)

My mental TODO list looked something like this:
1) Drop the optimization which checks against addr between _stext and
   _etext, as this skips __init functions on most archs.
2) Only put in the symbols for functions (currently CONFIG_KALLSYMS=y
   adds 400k on my laptop: ouch!).
3) Keith asked me to rename it, so as not to get confused with the
   previous patches and kgdb support).  I guess it's too late for this
   one.
4) Use a simple scheme like the mini-oopser did to reduce the symbol
   table size furthur (I got it down to 70k IIRC).
5) See if Kai prefers the compile step inside the Makefile rather than
   in the script.
6) It'd be nice if CONFIG_KALLSYMS=m worked.

If someone wants to champion any or all of these, be my guest, there's
plenty to go around 8)

Cheers,
Rusty.
--
  Anyone who quotes me in their sig is an idiot. -- Rusty Russell.

Re: kksymoops

[Kai Germaschewski]

On Wed, 20 Nov 2002, Rusty Russell wrote:

> In message <3DD9AB88.4000102@pobox.com> you write:
> > I'm _not_ asking "when", just wondering what the plan is to resuscitate 
> > kksymoops.
> 
> Looks like someone pushed my patch.  Erm, OK, wonder if it works on
> x86? 8)

I think Linus himself did that ;)

> My mental TODO list looked something like this:
> 1) Drop the optimization which checks against addr between _stext and
>    _etext, as this skips __init functions on most archs.

Well, this was put in to avoid all kind of garbage in the traces, so it 
shouldn't just go without replacement. Probably one could even get it 
correct now, using ->module_init() and ->module_core() (just set them for 
the core kernel as well).

> 2) Only put in the symbols for functions (currently CONFIG_KALLSYMS=y
>    adds 400k on my laptop: ouch!).

I'm not to sure about this, I sometimes find it useful to have variables 
on the stack identified correctly.

> 3) Keith asked me to rename it, so as not to get confused with the
>    previous patches and kgdb support).  I guess it's too late for this
>    one.

Nothing wrong with a follow-up patch, is it?

> 5) See if Kai prefers the compile step inside the Makefile rather than
>    in the script.

I'll actually have to look into this. The script is probably fine.

> 6) It'd be nice if CONFIG_KALLSYMS=m worked.

Shouldn't be too hard.

Well, I know talk is cheap. I'll try to find some time to actually look
into some of these issues and come up with patches.

--Kai

Re: kksymoops

[Jeff Garzik]

Jeff Garzik wrote:

> Rusty,
>
> What is the status of kksymoops?



LOL -- look at me eat my words.

I see it's now in Linus's tree -- thanks much!

	Jeff

Re: Module Refcount & Stuff mini-FAQ

[Pavel Machek]

Hi!

> Q: How does the module remove code work?
> A: It stops the machine by scheduling threads for every other CPU,
>    then they all disable interrupts.  At this stage we know that noone
>    is in try_module_get(), so we can reliably read the counter.  If
>    zero, or the rmmod user specified --wait, we set the live flag to
>    false.  After this, the reference count should not increase, and
>    each module_put() will wake us up, so we can check the counter
>    again.

Where is this implemented? I guess I need this for swsusp...

								Pavel
-- 
Worst form of spam? Adding advertisment signatures ala sourceforge.net.
What goes next? Inserting advertisment *into* email?

Re: Module Refcount & Stuff mini-FAQ

[Rusty Russell]

In message <20021123222334.GB5170@elf.ucw.cz> you write:
> Hi!
> 
> > Q: How does the module remove code work?
> > A: It stops the machine by scheduling threads for every other CPU,
> >    then they all disable interrupts.  At this stage we know that noone
> >    is in try_module_get(), so we can reliably read the counter.  If
> >    zero, or the rmmod user specified --wait, we set the live flag to
> >    false.  After this, the reference count should not increase, and
> >    each module_put() will wake us up, so we can check the counter
> >    again.
> 
> Where is this implemented? I guess I need this for swsusp...

I'm not so sure, but it's worth a look.  Look for stop_refcounts() in
module.c.  BTW, I call this a "bogolock".

Rusty.
--
  Anyone who quotes me in their sig is an idiot. -- Rusty Russell.

Re: kksymoops

[Kevin Brosius]

> Jeff Garzik wrote:
> 
> > Rusty,
> >
> > What is the status of kksymoops?
> 
> 
> 
> LOL -- look at me eat my words.
> 
> I see it's now in Linus's tree -- thanks much!
> 

Thanks guys! (I figured I'd give him a day or two before pinging Rusty
directly.)  This'll help chase some driver problems on the USB side.

-- 
Kevin