I all,
I was reading "Unreliable Guide To Locking" by Rusty Russell:
http://www.kernel.org/pub/linux/kernel/people/rusty/kernel-locking/index.html
but the table (named Cheat Sheet For Locking) is quite confusing me:
http://www.kernel.org/pub/linux/kernel/people/rusty/kernel-locking/c214.html#MINIMUM-LOCK-REQIREMENTS
maybe it is this really _cheating_ and _unreliable_ :-(
So I want to ask you a two questions:
1. following the table it seems that, if there is a critical section
only in one place in user context, no locking is needed (if you cross
"User Context A" with "User Context A" you get "None"). But as far as I
know, if you have critical section in a "read" syscall for example, you
must use some locking because two user processes can read the same
device at the same time.
2. Why spin_lock_irqsave is used only between "IRQ Handler A" and "IRQ
Handler B"? In all other situation spin_lock_irq is used instead. As far
as I know you can use this function (spin_lock_irq) only if you are
absolutely sure interrupts are not already disabled. So my question is
how can we be absolutely sure in all this situation that interrupts are
not already disabled.
Thank you in advance
Luca Ellero
--
To unsubscribe from this list: send an email with
"unsubscribe kernelnewbies" to ecartis@xxxxxxxxxxxx
Please read the FAQ at http://kernelnewbies.org/FAQ
