Messages in this thread | | | Date | Wed, 13 Mar 2019 16:48:53 -0700 | From | "Paul E. McKenney" <> | Subject | Re: [PATCH 1/3] list_bl: Add hlist_bl_add_before/behind helpers |
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On Thu, Feb 28, 2019 at 04:32:02PM -0500, Mike Snitzer wrote: > On Thu, Dec 20 2018 at 1:06pm -0500, > Nikos Tsironis <ntsironis@arrikto.com> wrote: > > > Add hlist_bl_add_before/behind helpers to add an element before/after an > > existing element in a bl_list. > > > > Signed-off-by: Nikos Tsironis <ntsironis@arrikto.com> > > Signed-off-by: Ilias Tsitsimpis <iliastsi@arrikto.com> > > --- > > include/linux/list_bl.h | 27 +++++++++++++++++++++++++++ > > 1 file changed, 27 insertions(+) > > > > diff --git a/include/linux/list_bl.h b/include/linux/list_bl.h > > index 3fc2cc57ba1b..2fd918e5fd48 100644 > > --- a/include/linux/list_bl.h > > +++ b/include/linux/list_bl.h > > @@ -86,6 +86,33 @@ static inline void hlist_bl_add_head(struct hlist_bl_node *n, > > hlist_bl_set_first(h, n); > > } > > > > +static inline void hlist_bl_add_before(struct hlist_bl_node *n, > > + struct hlist_bl_node *next) > > +{ > > + struct hlist_bl_node **pprev = next->pprev; > > + > > + n->pprev = pprev; > > + n->next = next; > > + next->pprev = &n->next; > > + > > + /* pprev may be `first`, so be careful not to lose the lock bit */ > > + WRITE_ONCE(*pprev, > > + (struct hlist_bl_node *) > > + ((unsigned long)n | > > + ((unsigned long)*pprev & LIST_BL_LOCKMASK)));
A nit, but use of uintptr_t shrinks things a bit:
+ (struct hlist_bl_node *) + ((uintptr_t)n | ((uintptr_t)*pprev & LIST_BL_LOCKMASK)));
I am not too concerned about this, though.
The WRITE_ONCE() is to handle races with hlist_bl_empty() (which does contain the corresponding READ_ONCE()) correct?
> > +} > > + > > +static inline void hlist_bl_add_behind(struct hlist_bl_node *n, > > + struct hlist_bl_node *prev) > > +{ > > + n->next = prev->next; > > + n->pprev = &prev->next; > > + WRITE_ONCE(prev->next, n);
I don't see what this WRITE_ONCE() is interacting with. The traversals use plain C-language reads, and hlist_bl_empty() can't get here. All uses of hlist_bl_for_each_entry() invoke hlist_bl_lock() before starting the traversal, and hlist_bl_for_each_entry_safe() looks to be unused. (Perhaps it should be removed? Or is there some anticipated use?)
I don't believe that the WRITE_ONCE() is needed. What am I missing?
Other than that, looks good.
Thanx, Paul
> > + > > + if (n->next) > > + n->next->pprev = &n->next; > > +} > > + > > static inline void __hlist_bl_del(struct hlist_bl_node *n) > > { > > struct hlist_bl_node *next = n->next; > > -- > > 2.11.0 > > Hi Paul and Christoph, > > You've added your Signed-off-by to include/linux/list_bl.h commits in > the past. I'm not sure how this proposed patch should be handled. > > These new hlist_bl_add_{before,behind} changes are a prereq for > dm-snapshot changes that Nikos has proposed, please see: > https://patchwork.kernel.org/patch/10739265/ > > Any assistance/review you, or others on LKML, might be able to provide > would be appreciated. > > Thanks, > Mike >
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