On Thu, 2009-07-16 at 08:59 -0400, James H. Anderson wrote:
>
> Raistlin wrote:
> > Also, I'm not sure I can find in the FMLP paper information about the
> > possibility of a task to suspend itself (e.g., I/O completion) while
> > holding a short lock... I assume this is not recommended, but may be
> > wrong, and, in that case, I hope Prof. Anderson and Bjorn will excuse
> > and correct me. :-)
> >
> >
> This is a really excellent point and something I probably should have
> mentioned. We developed the FMLP strictly for real-time (only)
> workloads. We were specifically looking at protecting memory-resident
> resources (not I/O). The FMLP would have to be significantly extended
> to work in settings where these assumptions don't hold.
One thing I've been thinking about is extending lockdep to help verify
things like this.
If we were to annotate a syscall/trap with something like:
lockdep_assume_rt()
And teach lockdep about non-RT blocking objects, we could validate that
the callchain down from lockdep_assume_rt() would not indeed contain a
non-RT resource, but also that we don't take locks which might in other
another code path.
That is, suppose:
sys_foo()
lockdep_assume_rt()
mutex_lock(&my_lock)
vs
sys_bar()
mutex_lock(&my_lock)
down_read(&mm->mmap_sem)
vs
page-fault
down_read(&mm->mmap_sem)
lock_page(page)
Would indeed generate a warning because mmap_sem is known to block on
IO, and there is a dependency (through sys_bar()) between my_lock and
mmap_sem, therefore sys_foo()'s assumption is invalid.
--
To unsubscribe from this list: send the line "unsubscribe linux-rt-users" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
