linux-kernel - Re: [PATCH 01/31] rhashtable: Allow rhashtable to be used from irq-safe contexts

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Message-ID: <Y4eMIVbgFgbxcMhr@slm.duckdns.org>
Date:   Wed, 30 Nov 2022 07:00:17 -1000
From:   Tejun Heo <tj@...nel.org>
To:     Linus Torvalds <torvalds@...ux-foundation.org>
Cc:     mingo@...hat.com, peterz@...radead.org, juri.lelli@...hat.com,
        vincent.guittot@...aro.org, dietmar.eggemann@....com,
        rostedt@...dmis.org, bsegall@...gle.com, mgorman@...e.de,
        bristot@...hat.com, vschneid@...hat.com, ast@...nel.org,
        daniel@...earbox.net, andrii@...nel.org, martin.lau@...nel.org,
        joshdon@...gle.com, brho@...gle.com, pjt@...gle.com,
        derkling@...gle.com, haoluo@...gle.com, dvernet@...a.com,
        dschatzberg@...a.com, dskarlat@...cmu.edu, riel@...riel.com,
        linux-kernel@...r.kernel.org, bpf@...r.kernel.org,
        kernel-team@...a.com
Subject: Re: [PATCH 01/31] rhashtable: Allow rhashtable to be used from
 irq-safe contexts

Hello,

On Wed, Nov 30, 2022 at 08:35:13AM -0800, Linus Torvalds wrote:
> On Wed, Nov 30, 2022 at 12:23 AM Tejun Heo <tj@...nel.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.

Sure thing.

> 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")

Yeah, it always feels kinda weird to wrap irqsave/restore due to the special
reference passing.

> 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.

Hahaha, that's gonna be an epic patchset.

Thanks.

-- 
tejun