Re: [PATCH] locking/local_lock, mm: Replace localtry_ helpers with local_trylock_t type

[Vlastimil Babka]

On 4/2/25 09:30, Sebastian Andrzej Siewior wrote:
> On 2025-03-31 17:51:34 [-0700], Alexei Starovoitov wrote:
>> From: Alexei Starovoitov <ast@xxxxxxxxxx>
>> 
>> Partially revert commit 0aaddfb06882 ("locking/local_lock: Introduce localtry_lock_t").
>> Remove localtry_*() helpers, since localtry_lock() name might
>> be misinterpreted as "try lock".
> 
> So we back to what you suggested initially. I was more a fan of
> explicitly naming things but if this is misleading so be it. So
> 
> Acked-by: Sebastian Andrzej Siewior <bigeasy@xxxxxxxxxxxxx>
> 
> While at it, could you look at the hunk below and check if it worth it?
> The struct duplication and hoping that the first part remains the same,
> is hoping. This still relies that the first part remains the same but…

I've updated your fixups to v2
https://lore.kernel.org/all/20250401205245.70838-1-alexei.starovoitov@xxxxxxxxx/

and to support runtime local_trylock_init(), and it's at the end of my e-mail

But I also thought we could go all the way with removing casting in
that way and stop relying on the same layout implicitly.

So I rewrote this:

#define __local_lock_acquire(lock)                                      \
        do {                                                            \
                local_trylock_t *tl;                                    \
                local_lock_t *l;                                        \
                                                                        \
                _Generic((lock),                                        \
                        local_lock_t *: ({                      	\
                                l = this_cpu_ptr(lock);                 \
                        }),                                             \
                        local_trylock_t *: ({                   	\
                                tl = this_cpu_ptr(lock);                \
                                l = &tl->llock;                         \
                                lockdep_assert(tl->acquired == 0);      \
                                WRITE_ONCE(tl->acquired, 1);            \
                        }),                                             \
                        default:(void)0);                               \
                local_lock_acquire(l);                                  \
        } while (0)

But I'm getting weird errors:

./include/linux/local_lock_internal.h:107:36: error: assignment to ‘local_trylock_t *’ from incompatible pointer type ‘local_lock_t *’ [-Wincompatible-pointer-types]
  107 |                                 tl = this_cpu_ptr(lock);                \

coming from the guard expansions. I don't understand why it goes to the
_Generic() "branch" of local_trylock_t * with a local_lock_t *.

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