Hi Rodolfo, On 7/28/07, Rodolfo Giometti <[EMAIL PROTECTED]> wrote: > On Fri, Jul 27, 2007 at 01:40:14PM -0600, Chris Friesen wrote: > > > > My point is that the lock should be used to protect specific data. Thus, it > > would be more correct to say, "spinlock foo is taken because > > pps_register_source() accesses variable bar". > > > > That way, if someone else wants to access "bar", they know that they need > > to take lock "foo". > > Ah, ok! I see. :)
I only glanced through the code, so could be wrong, but I noticed that the only global / shared data you have in there is a global "pps_source" array of pps_s structs. That's accessed / modified from the various syscalls introduced in the API exported to userspace, as well as the register/unregister/pps_event API exported to in-kernel client subsystems, yes? So it looks like you need to introduce proper locking for it, simply type-qualifying it as "volatile" is not enough. However, I think you've introduced two locks for it. The syscalls (that run in process context, obviously) seem to use a pps_mutex and pps_event() seems to be using the pps_lock spinlock (because that gets executed from interrupt context) -- and from the looks of it, the register/unregister functions are using /both/ the mutex and spinlock (!) This isn't quite right, (in fact there's nothing to protect pps_event from racing against a syscall), so you should use *only* the spinlock for synchronization -- the spin_lock_irqsave/restore() variants, in fact. [ Also, have you considered making pps_source a list and not an array? It'll help you lose a whole lot of MAX_SOURCES, pps_is_allocated, etc kind of gymnastics in there, and you _can_ return a pointer to the corresponding pps source struct from the register() function to the in-kernel users, so that way you get to retain the O(1) access to the corresponding source when a client calls into pps_event(), similar to how you're using the array index presently. ] I also noticed code like (from pps_event): + /* Try to grab the lock, if not we prefere loose the event... */ + if (!spin_trylock(&pps_lock)) + return; which looks worrisome and unnecessary. That spinlock looks to be of fine enough granularity to me, do you think there'd be any contention on it? I /think/ you can simply make that a spin_lock(). Overall the code looks simple / straightforward enough to me (except for the parport / uart stuff that I have no clue about), and I'll also read up on the relevant RFC for this and would hopefully try and give you a more meaningful review over the weekend. Thanks, Satyam - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/