Re: [PATCH v4 tip/perf/core 1/4] mm: Convert mm_lock_seq to a proper seqcount

[Suren Baghdasaryan <surenb@google.com>]

On Thu, Nov 21, 2024 at 4:40 AM Peter Zijlstra <peterz@infradead.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);
> > +}