linux-kernel - Re: [PATCH v4 tip/perf/core 1/4] mm: Convert mm_lock

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Message-ID: <CAJuCfpEBJsR803Ac-cwN0MWadzWW_WKZchaexdJauYETaww40w@mail.gmail.com>
Date: Thu, 21 Nov 2024 07:35:12 -0800
From: Suren Baghdasaryan <surenb@...gle.com>
To: Peter Zijlstra <peterz@...radead.org>
Cc: Andrii Nakryiko <andrii@...nel.org>, linux-trace-kernel@...r.kernel.org, 
	linux-mm@...ck.org, akpm@...ux-foundation.org, oleg@...hat.com, 
	rostedt@...dmis.org, mhiramat@...nel.org, bpf@...r.kernel.org, 
	linux-kernel@...r.kernel.org, jolsa@...nel.org, paulmck@...nel.org, 
	willy@...radead.org, mjguzik@...il.com, brauner@...nel.org, jannh@...gle.com, 
	mhocko@...nel.org, vbabka@...e.cz, shakeel.butt@...ux.dev, hannes@...xchg.org, 
	Liam.Howlett@...cle.com, lorenzo.stoakes@...cle.com, david@...hat.com, 
	arnd@...db.de, richard.weiyang@...il.com, zhangpeng.00@...edance.com, 
	linmiaohe@...wei.com, viro@...iv.linux.org.uk, hca@...ux.ibm.com
Subject: Re: [PATCH v4 tip/perf/core 1/4] mm: Convert mm_lock_seq to a proper seqcount

On Thu, Nov 21, 2024 at 4:40 AM Peter Zijlstra <peterz@...radead.org> wrote:
>
> On Sun, Oct 27, 2024 at 06:08:15PM -0700, Andrii Nakryiko wrote:
> > +/*
> > + * Drop all currently-held per-VMA locks.
> > + * This is called from the mmap_lock implementation directly before releasing
> > + * a write-locked mmap_lock (or downgrading it to read-locked).
> > + * This should normally NOT be called manually from other places.
> > + * If you want to call this manually anyway, keep in mind that this will release
> > + * *all* VMA write locks, including ones from further up the stack.
> > + */
> > +static inline void vma_end_write_all(struct mm_struct *mm)
> > +{
> > +     mmap_assert_write_locked(mm);
> > +     /*
> > +      * Nobody can concurrently modify mm->mm_lock_seq due to exclusive
> > +      * mmap_lock being held.
> > +      */
>
> You can write:
>
>         ASSERT_EXCLUSIVE_WRITER(mm->mm_lock_seq);
>
> instead of that comment. Then KCSAN will validate the claim.

Thanks for the tip! This one looks not critical but I see there are
more important comments in "mm: Introduce
mmap_lock_speculation_{begin|end}". I'll send a new version shortly.

>
> > +     mm_lock_seqcount_end(mm);
> > +}