Re: [PATCH v2] lock/semaphore: Avoid an unnecessary deadlock within up()

[Sergey Senozhatsky]

On (02/03/16 08:28), Ingo Molnar wrote:
[..]
> So why not move printk away from semaphores? Semaphores are classical constructs 
> that have legacies and are somewhat non-obvious to use, compared to modern, 
> simpler locking primitives. I'd not touch their implementation, unless we are 
> absolutely sure this is a safe optimization.

semaphore's spin_lock is not the only spin lock that printk acquires. it also takes the
logbuf_lock (and different locks in console drivers (up to console driver)).

Jan Kara posted a patch that offloads printing job (console_trylock()-console_unlock())
from printk() call (when printk can offload it). so semaphore and console driver's locks
will go away (mostly) with Jan's patch. logbug spin_lock, however, will stay.

	-ss