Hi Mathieu, On Thu, Feb 5, 2015 at 10:06 PM, Mathieu Desnoyers <[email protected]> wrote: > A smp_read_barrier_depends() appears to be missing in llist_del_first(). > It should only matter for Alpha in practice. Adding it after the check > of entry against NULL allows skipping the barrier in a common case.
We recently decided on using lockless_dereference() instead of hard-coding smp_read_barrier_depends()[1]. The advantage is that lockless_dereference() clearly shows what loads are being ordered. Could you resend the patch using that API? Thanks! [1] http://lkml.iu.edu/hypermail/linux/kernel/1410.3/04561.html > > Signed-off-by: Mathieu Desnoyers <[email protected]> > CC: Huang Ying <[email protected]> > CC: Paul McKenney <[email protected]> > CC: David Howells <[email protected]> > --- > lib/llist.c | 7 +++++++ > 1 file changed, 7 insertions(+) > > diff --git a/lib/llist.c b/lib/llist.c > index f76196d..72861f3 100644 > --- a/lib/llist.c > +++ b/lib/llist.c > @@ -26,6 +26,7 @@ > #include <linux/export.h> > #include <linux/interrupt.h> > #include <linux/llist.h> > +#include <asm/barrier.h> > > > /** > @@ -72,6 +73,12 @@ struct llist_node *llist_del_first(struct llist_head *head) > if (entry == NULL) > return NULL; > old_entry = entry; > + /* > + * Load entry before entry->next. Matches the implicit > + * memory barrier before the cmpxchg in llist_add_batch(), > + * which ensures entry->next is stored before entry. > + */ > + smp_read_barrier_depends(); > next = entry->next; > entry = cmpxchg(&head->first, old_entry, next); > if (entry == old_entry) > -- > 2.1.4 > > -- > To unsubscribe from this list: send the line "unsubscribe linux-kernel" in > the body of a message to [email protected] > More majordomo info at http://vger.kernel.org/majordomo-info.html > Please read the FAQ at http://www.tux.org/lkml/ -- Pranith -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
