On 21.09.23 18:48, Kinsey Moore wrote:
On Thu, Sep 21, 2023 at 10:23 AM Sebastian Huber
<sebastian.hu...@embedded-brains.de
<mailto:sebastian.hu...@embedded-brains.de>> wrote:
On 21.09.23 17:06, Kinsey Moore wrote:
> On Thu, Sep 21, 2023 at 10:01 AM Sebastian Huber
> <sebastian.hu...@embedded-brains.de
<mailto:sebastian.hu...@embedded-brains.de>
> <mailto:sebastian.hu...@embedded-brains.de
<mailto:sebastian.hu...@embedded-brains.de>>> wrote:
>
> On 21.09.23 16:52, Kinsey Moore wrote:
> > On Thu, Sep 21, 2023 at 9:47 AM Sebastian Huber
> > <sebastian.hu...@embedded-brains.de
<mailto:sebastian.hu...@embedded-brains.de>
> <mailto:sebastian.hu...@embedded-brains.de
<mailto:sebastian.hu...@embedded-brains.de>>
> > <mailto:sebastian.hu...@embedded-brains.de
<mailto:sebastian.hu...@embedded-brains.de>
> <mailto:sebastian.hu...@embedded-brains.de
<mailto:sebastian.hu...@embedded-brains.de>>>> wrote:
> >
> > On 20.09.23 20:35, Kinsey Moore wrote:
> > [...]
> > > @@ -1306,8 +1307,22 @@ static void
process_delayed_work(void)
> > > while (!rtems_chain_is_tail(&process_work_chain,
> node)) {
> > > work = (struct delayed_work*) node;
> > > rtems_chain_node* next_node =
> rtems_chain_next(node);
> > > +
> > > + /*
> > > + * Don't leave extracted node exposed
to other
> > operations
> > > + * under RTEMS_DEBUG
> > > + */
> > > +#ifdef RTEMS_DEBUG
> > > + mutex_lock(&delayed_work_mutex);
> > > +#endif
> > > rtems_chain_extract(node);
> > > +#ifdef RTEMS_DEBUG
> > > + node->next = node;
> > > + mutex_unlock(&delayed_work_mutex);
> > > +#endif
> > > +
> > > work->callback(&work->work);
> > > + rtems_chain_set_off_chain(node);
> > > node = next_node;
> > > }
> > > }
> >
> > This change makes no sense to me. The code should work
> regardless if
> > RTEMS_DEBUG is defined or not.
> >
> >
> > RTEMS_DEBUG introduces a behavioral change in
> rtems_chain_extract() such
> > that extracted nodes are automatically set off-chain. When
> RTEMS_DEBUG
> > is not set, node->next is left untouched. This has to be
managed
> because
> > this code needs the node to remain on-chain so that it is not
> re-queued
> > during the operation.
>
> Yes, but while a node is on a chain you must not call
> rtems_chain_set_off_chain(). If you want to use the off-chain
state,
> then you have to use this:
>
> rtems_chain_extract(node);
> rtems_chain_set_off_chain(node);
>
> or
>
> rtems_chain_extract_unprotected(node);
> rtems_chain_set_off_chain(node);
>
> The automatic set off-chain in RTEMS_DEBUG is just to ensure
that basic
> chain operations are used in the right state.
>
>
> Yes, there is no behavior here where rtems_chain_set_off_chain() is
> being called on a node that is still in a chain. This section of
code is
> entirely managing the side-effect of RTEMS_DEBUG that sets the
node in
> the off-chain state post-extraction. In this case, that
side-effect is
> undesirable and so a lock is in place to prevent that temporary
> side-effect from leaking to other parts of the system since all
other
> off-chain checks are behind the same lock.
Ok, so you want to delay the set-off state visibility in case
RTEMS_DEBUG is defined. This is the first place in the code base which
needs this behaviour.
Would it be more acceptable to always lock it and ensure that it's
recognized as on-chain instead of checking for RTEMS_DEBUG?
We basically don't use internal locking in JFFS2 in RTEMS. Why can't
you
use the global file system lock of the JFFS2 instance to work carry out
this delayed work?
The JFFS2 instance to which the delayed work belongs is a detail
internal to the delayed work itself. Reaching that information is
possible, but would be fragile. The other option I had in mind was to
create one delayed work thread per JFFS2 FS instance so that the delayed
work processor can know reliably which JFFS2 instance it is working on,
but that seemed wasteful.
I would do the following.
1. The delayed work support uses a mutex D and a condition variable C
used with D.
2. Add a queue for the delayed work to the fs information and a node to
register the info in the delayed work support.
3. The first delayed work request of a JFFS2 instance registers the fs
information in the delayed work support and uses C to signal the work to
the delayed work task.
4. Further requests just get enqueued and signaled using D and C.
5. When a instance is unmounted, drain the delayed work queue using D and C.
The delayed work uses the fs info mutex to protect the work. You need
also reference count for the fs info to control the work and the drain
during unmount.
--
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