locking/local_lock, mm: Replace localtry_ helpers with local_trylock_t type

locking/local_lock, mm: Replace localtry_ helpers with local_trylock_t type

Partially revert commit 0aaddfb06882 ("locking/local_lock: Introduce localtry_lock_t").
Remove localtry_*() helpers, since localtry_lock() name might
be misinterpreted as "try lock".

Introduce local_trylock[_irqsave]() helpers that only work
with newly introduced local_trylock_t type.
Note that attempt to use local_trylock[_irqsave]() with local_lock_t
will cause compilation failure.

Usage and behavior in !PREEMPT_RT:

local_lock_t lock;                     // sizeof(lock) == 0
local_lock(&lock);                     // preempt disable
local_lock_irqsave(&lock, ...);        // irq save
if (local_trylock_irqsave(&lock, ...)) // compilation error

local_trylock_t lock;                  // sizeof(lock) == 4
local_lock(&lock);                     // preempt disable, acquired = 1
local_lock_irqsave(&lock, ...);        // irq save, acquired = 1
if (local_trylock(&lock))              // if (!acquired) preempt disable
if (local_trylock_irqsave(&lock, ...)) // if (!acquired) irq save

The existing local_lock_*() macros can be used either with
local_lock_t or local_trylock_t.
With local_trylock_t they set acquired = 1 while local_unlock_*() clears it.

In !PREEMPT_RT local_lock_irqsave(local_lock_t *) disables interrupts
to protect critical section, but it doesn't prevent NMI, so the fully
reentrant code cannot use local_lock_irqsave(local_lock_t *) for
exclusive access.

The local_lock_irqsave(local_trylock_t *) helper disables interrupts
and sets acquired=1, so local_trylock_irqsave(local_trylock_t *) from
NMI attempting to acquire the same lock will return false.

In PREEMPT_RT local_lock_irqsave() maps to preemptible spin_lock().
Map local_trylock_irqsave() to preemptible spin_trylock().
When in hard IRQ or NMI return false right away, since
spin_trylock() is not safe due to explicit locking in the underneath
rt_spin_trylock() implementation. Removing this explicit locking and
attempting only "trylock" is undesired due to PI implications.

The local_trylock() without _irqsave can be used to avoid the cost of
disabling/enabling interrupts by only disabling preemption, so
local_trylock() in an interrupt attempting to acquire the same
lock will return false.

Note there is no need to use local_inc for acquired variable,
since it's a percpu variable with strict nesting scopes.

Acked-by: Vlastimil Babka <vbabka@suse.cz>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>