Re: [PATCH 4/7] sempahore: add a helper for a concurrency limiter

[Sergey Senozhatsky]

On (23/03/30 09:23), Linus Torvalds wrote:
> Although we also do have some other issues - I think down_trylock() is
> ok in irq contexts, but mutex_trylock() is not. Maybe that's why
> printk uses semaphores? I forget.

Yes, correct. IIRC we also cannot safely call mutex_unlock() from IRQ
context because it takes some internal mutex spin_lock in a non-IRQ-safe
manner. Semaphore is OK in this regard, both semaphore try_lock() and
unlock() can be called from IRQ.