klist: don't iterate over deleted entries

A klist entry is kept on the list till all its current iterations are
finished; however, a new iteration after deletion also iterates over
deleted entries as long as their reference count stays above zero.
This causes problems for cases where there are users which iterate
over the list while synchronized against list manipulations and
natuarally expect already deleted entries to not show up during
iteration.

This patch implements dead flag which gets set on deletion so that
iteration can skip already deleted entries.  The dead flag piggy backs
on the lowest bit of knode->n_klist and only visible to klist
implementation proper.

While at it, drop klist_iter->i_head as it's redundant and doesn't
offer anything in semantics or performance wise as klist_iter->i_klist
is dereferenced on every iteration anyway.

Signed-off-by: Tejun Heo <tj@kernel.org>
Cc: Greg Kroah-Hartman <gregkh@suse.de>
Cc: Alan Stern <stern@rowland.harvard.edu>
Cc: Jens Axboe <jens.axboe@oracle.com>
Signed-off-by: Jens Axboe <jens.axboe@oracle.com>

1 files changed, 1 insertions, 2 deletions

diff --git a/include/linux/klist.h b/include/linux/klist.h
index 06c338ef7f1b..8ea98db223e5 100644
--- a/include/linux/klist.h
+++ b/include/linux/klist.h
@@ -38,7 +38,7 @@ extern void klist_init(struct klist *k, void (*get)(struct klist_node *),
                        void (*put)(struct klist_node *));
 
 struct klist_node {
-        struct klist            *n_klist;
+        void                    *n_klist;       /* never access directly */
         struct list_head        n_node;
         struct kref             n_ref;
         struct completion       n_removed;
@@ -57,7 +57,6 @@ extern int klist_node_attached(struct klist_node *n);
 
 struct klist_iter {
         struct klist            *i_klist;
-        struct list_head        *i_head;
         struct klist_node       *i_cur;
 };