};
#define IO_POLL_CANCEL_FLAG BIT(31)
-#define IO_POLL_REF_MASK GENMASK(30, 0)
+#define IO_POLL_RETRY_FLAG BIT(30)
+#define IO_POLL_REF_MASK GENMASK(29, 0)
+
+/*
+ * We usually have 1-2 refs taken, 128 is more than enough and we want to
+ * maximise the margin between this amount and the moment when it overflows.
+ */
+#define IO_POLL_REF_BIAS 128
+
+static bool io_poll_get_ownership_slowpath(struct io_kiocb *req)
+{
+ int v;
+
+ /*
+ * poll_refs are already elevated and we don't have much hope for
+ * grabbing the ownership. Instead of incrementing set a retry flag
+ * to notify the loop that there might have been some change.
+ */
+ v = atomic_fetch_or(IO_POLL_RETRY_FLAG, &req->poll_refs);
+ if (v & IO_POLL_REF_MASK)
+ return false;
+ return !(atomic_fetch_inc(&req->poll_refs) & IO_POLL_REF_MASK);
+}
/*
* If refs part of ->poll_refs (see IO_POLL_REF_MASK) is 0, it's free. We can
*/
static inline bool io_poll_get_ownership(struct io_kiocb *req)
{
+ if (unlikely(atomic_read(&req->poll_refs) >= IO_POLL_REF_BIAS))
+ return io_poll_get_ownership_slowpath(req);
return !(atomic_fetch_inc(&req->poll_refs) & IO_POLL_REF_MASK);
}
*/
if ((v & IO_POLL_REF_MASK) != 1)
req->result = 0;
+ if (v & IO_POLL_RETRY_FLAG) {
+ req->result = 0;
+ /*
+ * We won't find new events that came in between
+ * vfs_poll and the ref put unless we clear the
+ * flag in advance.
+ */
+ atomic_andnot(IO_POLL_RETRY_FLAG, &req->poll_refs);
+ v &= ~IO_POLL_RETRY_FLAG;
+ }
if (!req->result) {
struct poll_table_struct pt = { ._key = poll->events };