[lkml]   [2003]   [Nov]   [24]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
Messages in this thread
    SubjectRe: Fix locking in input

    > >>input uses "volatile signed char" as a shared variable between normal
    > >>and interrupt threads (look at _sendbyte()). Thats bad idea, this
    > >>switches it to atomic_t.
    > >
    > >This change looks unnecessary to me - we aren't trying to increment or
    > >decrement the variable, just set it and read it. Reading and writing
    > >individual bytes is atomic on any platform we care about.
    > >
    > >
    > I think one platform (early ARM?) cannot access bytes directly, and
    > implement the access with read 16-bit, change 8-bit, write back 16 bit.
    > Reading/writing pointers or longs is atomic.
    > Pavel: Do you know that atomic_set and atomic_read aren't memory barriers?
    > I.e.
    > - psmouse->ack = 0;
    > + atomic_set(&psmouse->ack, 0);
    > psmouse->acking = 1;
    > It's not guaranteed that all cpus will see psmouse->ack=0 before
    > psmouse->acking=1. And adding the required memory barriers usually makes
    > the code completely unreadable, thus I usually give up and switch to a
    > spinlock.

    Would simply adding mb() there fix it? It is not performance-critical
    in any way...

    When do you have a heart between your knees?
    [Johanka's followup: and *two* hearts?]
    To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
    the body of a message to
    More majordomo info at
    Please read the FAQ at

     \ /
      Last update: 2005-03-22 13:58    [W:0.022 / U:6.272 seconds]
    ©2003-2017 Jasper Spaans. hosted at Digital OceanAdvertise on this site