On Thu, 22 Nov 2012 09:18:34 +0100
Lukas Czerner <lczer...@redhat.com> wrote:
> New wait_event{_interruptible}_lock_irq{_cmd} macros added. This commit
> moves the private wait_event_lock_irq() macro from MD to regular wait
> includes, introduces new macro wait_event_lock_irq_cmd() instead of using
> the old method with omitting cmd parameter which is ugly and makes a use
> of new macros in the MD. It also introduces the _interruptible_ variant.
>
> The use of new interface is when one have a special lock to protect data
> structures used in the condition, or one also needs to invoke "cmd"
> before putting it to sleep. "cmd" is always invoked before checking the
> "condition" so in case it will change the condition outcome we would not
> have to sleep unnecessarily.
>
> All new macros are expected to be called with the lock taken. The lock
> is released before sleep and is reacquired afterwards. We will leave the
> macro with the lock held.
>
> Note to DM: IMO this should also fix theoretical race on waitqueue while
> using simultaneously wait_event_lock_irq() and wait_event() because of
> lack of locking around current state setting and wait queue removal.
>
> ...
>
> +#define __wait_event_lock_irq(wq, condition, lock, cmd)
> \
> +do { \
> + DEFINE_WAIT(__wait); \
> + \
> + cmd; \
> + for (;;) { \
> + prepare_to_wait(&wq, &__wait, TASK_UNINTERRUPTIBLE); \
> + if (condition) \
> + break; \
> + spin_unlock_irq(&lock); \
> + schedule(); \
> + cmd; \
> + spin_lock_irq(&lock); \
> + } \
> + finish_wait(&wq, &__wait); \
> +} while (0)
>
> ...
>
> +#define __wait_event_interruptible_lock_irq(wq, condition, \
> + lock, ret, cmd) \
> +do { \
> + DEFINE_WAIT(__wait); \
> + \
> + cmd; \
> + for (;;) { \
> + prepare_to_wait(&wq, &__wait, TASK_INTERRUPTIBLE); \
> + if (condition) \
> + break; \
> + if (signal_pending(current)) { \
> + ret = -ERESTARTSYS; \
> + break; \
> + } \
> + spin_unlock_irq(&lock); \
> + schedule(); \
> + cmd; \
> + spin_lock_irq(&lock); \
> + } \
> + finish_wait(&wq, &__wait); \
> +} while (0)
These could be combined - use
if (flags == TASK_INTERRUPTIBLE && signal_pending(current)) { \
ret = -ERESTARTSYS; \
break; \
} \
and the compiler will fully remove that code for the
__wait_event_lock_irq() case.
But that's all a pretty small gain, IMO.
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