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authorNeilBrown <neilb@suse.de>2023-09-11 10:39:37 -0400
committerChuck Lever <chuck.lever@oracle.com>2023-10-16 12:44:06 -0400
commit8a3e5975ed11dd16d81dc501b514ab01986db94e (patch)
tree1e14c66306c4e7463ab715a5e1ceed5768cdd438 /lib
parent9bd4161c591710f152a8cd3ed85ea928c61e26ca (diff)
downloadlwn-8a3e5975ed11dd16d81dc501b514ab01986db94e.tar.gz
lwn-8a3e5975ed11dd16d81dc501b514ab01986db94e.zip
llist: add llist_del_first_this()
llist_del_first_this() deletes a specific entry from an llist, providing it is at the head of the list. Multiple threads can call this concurrently providing they each offer a different entry. This can be uses for a set of worker threads which are on the llist when they are idle. The head can always be woken, and when it is woken it can remove itself, and possibly wake the next if there is an excess of work to do. Signed-off-by: NeilBrown <neilb@suse.de> Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
Diffstat (limited to 'lib')
-rw-r--r--lib/llist.c28
1 files changed, 28 insertions, 0 deletions
diff --git a/lib/llist.c b/lib/llist.c
index 6e668fa5a2c6..f21d0cfbbaaa 100644
--- a/lib/llist.c
+++ b/lib/llist.c
@@ -66,6 +66,34 @@ struct llist_node *llist_del_first(struct llist_head *head)
EXPORT_SYMBOL_GPL(llist_del_first);
/**
+ * llist_del_first_this - delete given entry of lock-less list if it is first
+ * @head: the head for your lock-less list
+ * @this: a list entry.
+ *
+ * If head of the list is given entry, delete and return %true else
+ * return %false.
+ *
+ * Multiple callers can safely call this concurrently with multiple
+ * llist_add() callers, providing all the callers offer a different @this.
+ */
+bool llist_del_first_this(struct llist_head *head,
+ struct llist_node *this)
+{
+ struct llist_node *entry, *next;
+
+ /* acquire ensures orderig wrt try_cmpxchg() is llist_del_first() */
+ entry = smp_load_acquire(&head->first);
+ do {
+ if (entry != this)
+ return false;
+ next = READ_ONCE(entry->next);
+ } while (!try_cmpxchg(&head->first, &entry, next));
+
+ return true;
+}
+EXPORT_SYMBOL_GPL(llist_del_first_this);
+
+/**
* llist_reverse_order - reverse order of a llist chain
* @head: first item of the list to be reversed
*