Re: Open Sound System - OSS "soundon" command causes KERNEL PANIC FreeBSD-11

From: Konstantin Belousov <kostikbel_at_gmail.com>
Date: Thu, 11 Feb 2016 12:40:27 +0200
On Thu, Feb 11, 2016 at 11:19:56AM +0100, Hans Petter Selasky wrote:
> On 02/11/16 11:14, Konstantin Belousov wrote:
> > On Thu, Feb 11, 2016 at 07:54:57AM +0100, Hans Petter Selasky wrote:
> >> On 02/11/16 03:02, Greg Quinlan wrote:
> >>> Hi HPS,
> >>> Note: Does not happen on FreeBSD 10.1-Stable!
> >>>
> >>
> >> Yes, that's because WITNESS is off in 10.x by default.
> >>
> >> Does the attached patch solve your problem?
>  >
> > No, the patch below does not solve the issue, it only papers over it.
> > I object against committing this change.
> 
> For cases where the returned pointer is not deferred, but only checked 
> for a module's presence in the kernel you don't need a lock to protect 
> anything. Maybe make a separate API for this?
How checking for bool (i.e. == NULL) would fix anything ?  The fact that
the module is loaded could be invalidated in parallel, so the answer you
get is already wrong.  The bool value you obtained is equally wrong.

> 
> >
> > Issue is that, if called unlocked, the result from module_lookupbyname()
> > could become invalid right after receiving.  It is the duty of the caller
> > of the function to ensure that the result is still valid, and the only
> > way to achieve it is to own the lock around the whole code region which
> > calls the function and utilizes its result.
> >
> > A bug is in the OSS code.
> 
> Yes, so why not factor out the solution? Maybe more port KLD's will trip 
> over this?
Solution is for OSS code to take a lock around the whole region where the
answer is needed.
Received on Thu Feb 11 2016 - 09:40:34 UTC

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