io_uring: refactor io_ring_exit_work()

Don't reinit io_ring_exit_work()'s exit work/completions on each
iteration, that's wasteful. Also add list_rotate_left(), so if we failed
to complete the task job, we don't try it again and again but defer it
until others are processed.

Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

diff --git a/fs/io_uring.c b/fs/io_uring.c
index a807c3f..f0e6349 100644 (file)
--- a/fs/io_uring.c
+++ b/fs/io_uring.c
@@ -8575,6 +8575,9 @@ static void io_ring_exit_work(struct work_struct *work)
                WARN_ON_ONCE(time_after(jiffies, timeout));
        } while (!wait_for_completion_timeout(&ctx->ref_comp, HZ/20));
 
+       init_completion(&exit.completion);
+       init_task_work(&exit.task_work, io_tctx_exit_cb);
+       exit.ctx = ctx;
        /*
         * Some may use context even when all refs and requests have been put,
         * and they are free to do so while still holding uring_lock or
@@ -8587,9 +8590,8 @@ static void io_ring_exit_work(struct work_struct *work)
 
                node = list_first_entry(&ctx->tctx_list, struct io_tctx_node,
                                        ctx_node);
-               exit.ctx = ctx;
-               init_completion(&exit.completion);
-               init_task_work(&exit.task_work, io_tctx_exit_cb);
+               /* don't spin on a single task if cancellation failed */
+               list_rotate_left(&ctx->tctx_list);
                ret = task_work_add(node->task, &exit.task_work, TWA_SIGNAL);
                if (WARN_ON_ONCE(ret))
                        continue;
@@ -8597,7 +8599,6 @@ static void io_ring_exit_work(struct work_struct *work)
 
                mutex_unlock(&ctx->uring_lock);
                wait_for_completion(&exit.completion);
-               cond_resched();
                mutex_lock(&ctx->uring_lock);
        }
        mutex_unlock(&ctx->uring_lock);