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From:   Linus Torvalds <torvalds@linux-foundation.org>
Date:   Wed, 30 Nov 2022 08:35:13 -0800
Message-ID: <CAHk-=wg8wvB4vo-PaCSMSRaCd2c+rk8OnE72eF+skDVMdk9LsA@mail.gmail.com>
Subject: Re: [PATCH 01/31] rhashtable: Allow rhashtable to be used from
 irq-safe contexts
To:     Tejun Heo <tj@kernel.org>
Cc:     mingo@redhat.com, peterz@infradead.org, juri.lelli@redhat.com,
        vincent.guittot@linaro.org, dietmar.eggemann@arm.com,
        rostedt@goodmis.org, bsegall@google.com, mgorman@suse.de,
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        daniel@iogearbox.net, andrii@kernel.org, martin.lau@kernel.org,
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On Wed, Nov 30, 2022 at 12:23 AM Tejun Heo <tj@kernel.org> wrote:
>
>
>  static inline void rht_lock(struct bucket_table *tbl,
> -                           struct rhash_lock_head __rcu **bkt)
> +                           struct rhash_lock_head __rcu **bkt,
> +                           unsigned long *flags)

I guess it doesn't matter as long as this actually gets inlined, but
wouldn't it be better to have

   flags = rht_lock(..);
   ...
   rht_unlock(.., flags);

as the calling convention? Rather than passing a pointer to the stack around.

That's what the native _raw_spin_lock_irqsave() interface is (even if
"spin_lock_irqsave()" itself for historical reasons uses that inline
asm-like "pass argument by reference *without* using a pointer")

And gaah, we should have made 'flags' be a real type long ago, but I
guess 'unsigned long' is too ingrained and traditional to change that
now.

              Linus