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    SubjectRe: [RFC PATCH 06/21] list: Remove superfluous WRITE_ONCE() from hlist_nulls implementation
    On Tue, Mar 24, 2020 at 03:36:28PM +0000, Will Deacon wrote:
    > Commit 860c8802ace1 ("rcu: Use WRITE_ONCE() for assignments to ->pprev
    > for hlist_nulls") added WRITE_ONCE() invocations to hlist_nulls_add_head()
    > and hlist_nulls_del().
    >
    > Since these functions should not ordinarily run concurrently with other
    > list accessors, restore the plain C assignments so that KCSAN can yell
    > if a data race occurs.
    >
    > Cc: Eric Dumazet <edumazet@google.com>
    > Cc: Paul E. McKenney <paulmck@kernel.org>
    > Cc: Peter Zijlstra <peterz@infradead.org>
    > Signed-off-by: Will Deacon <will@kernel.org>

    And this means that the lockless uses of hlist_nulls_empty() need
    attention, correct?

    Thanx, Paul

    > ---
    > include/linux/list_nulls.h | 6 +++---
    > 1 file changed, 3 insertions(+), 3 deletions(-)
    >
    > diff --git a/include/linux/list_nulls.h b/include/linux/list_nulls.h
    > index fa51a801bf32..fd154ceb5b0d 100644
    > --- a/include/linux/list_nulls.h
    > +++ b/include/linux/list_nulls.h
    > @@ -80,10 +80,10 @@ static inline void hlist_nulls_add_head(struct hlist_nulls_node *n,
    > struct hlist_nulls_node *first = h->first;
    >
    > n->next = first;
    > - WRITE_ONCE(n->pprev, &h->first);
    > + n->pprev = &h->first;
    > h->first = n;
    > if (!is_a_nulls(first))
    > - WRITE_ONCE(first->pprev, &n->next);
    > + first->pprev = &n->next;
    > }
    >
    > static inline void __hlist_nulls_del(struct hlist_nulls_node *n)
    > @@ -99,7 +99,7 @@ static inline void __hlist_nulls_del(struct hlist_nulls_node *n)
    > static inline void hlist_nulls_del(struct hlist_nulls_node *n)
    > {
    > __hlist_nulls_del(n);
    > - WRITE_ONCE(n->pprev, LIST_POISON2);
    > + n->pprev = LIST_POISON2;
    > }
    >
    > /**
    > --
    > 2.20.1
    >

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