Re: [ANNOUNCE] Kernel Janitor's TODO list

Manfred Spraul
2001-01-28T17:41:29Z

David Woodhouse wrote:
>
> TIOCMIWAIT does restore_flags() before interruptible_sleep_on(). It's
> broken too.
>
Yes, and I found a second bug: it doesn't sti() immediately after
interruptible_sleep_on(), thus cli() doesn't reacquire the global irq
lock --> the atomic copy won't be atomic on SMP.

And one more point for the Janitor's list:
Get rid of superflous irqsave()/irqrestore()'s - in 90% of the cases
either spin_lock_irq() or spin_lock() is sufficient. That's both faster
and better readable.

spin_lock_irq(): you know that the function is called with enabled
interrupts.
spin_lock(): can be used in hardware interrupt handlers when only one
hardware interrupt uses that spinlocks (most hardware drivers), or when
all hardware interrupt handler set the SA_INTERRUPT flag (e.g. rtc and
timer interrupt)

There is one more rule when you can use spin_lock_irq():
if you know that the function might sleep. E.g. compare make_request
from 2.2.18 and __make_request() from 2.4.
Since __get_request_wait() can sleep, the callers of make_request()
cannot rely on disabled interrupts, thus spin_lock_irq instead of
spin_lock_irqsave().

--
Manfred