Messages in this thread | | | Date | Sun, 23 Nov 2003 23:24:02 +0100 | From | Manfred Spraul <> | Subject | Re: Fix locking in input |
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Paul wrote:
>Pavel Machek writes: > >> 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.
-- Manfred
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