io_uring: fix work_exit sqpoll cancellations

After closing an SQPOLL ring, io_ring_exit_work() kicks in and starts
doing cancellations via io_uring_try_cancel_requests(). It will go
through io_uring_try_cancel_iowq(), which uses ctx->tctx_list, but as
SQPOLL task don't have a ctx note, its io-wq won't be reachable and so
is left not cancelled.

It will eventually cancelled when one of the tasks dies, but if a thread
group survives for long and changes rings, it will spawn lots of
unreclaimed resources and live locked works.

Cancel SQPOLL task's io-wq separately in io_ring_exit_work().

Cc: stable@vger.kernel.org
Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
Link: https://lore.kernel.org/r/a71a7fe345135d684025bb529d5cb1d8d6b46e10.1619389911.git.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 577520445fa0aadec784446e5a7b68f8afd3f9fc..f20622bd963b25975df9703ce88a689e3bb25b61 100644 (file)
--- a/fs/io_uring.c
+++ b/fs/io_uring.c
@@ -8679,6 +8679,13 @@ static void io_tctx_exit_cb(struct callback_head *cb)
        complete(&work->completion);
 }
 
+static bool io_cancel_ctx_cb(struct io_wq_work *work, void *data)
+{
+       struct io_kiocb *req = container_of(work, struct io_kiocb, work);
+
+       return req->ctx == data;
+}
+
 static void io_ring_exit_work(struct work_struct *work)
 {
        struct io_ring_ctx *ctx = container_of(work, struct io_ring_ctx, exit_work);
@@ -8695,6 +8702,17 @@ static void io_ring_exit_work(struct work_struct *work)
         */
        do {
                io_uring_try_cancel_requests(ctx, NULL, NULL);
+               if (ctx->sq_data) {
+                       struct io_sq_data *sqd = ctx->sq_data;
+                       struct task_struct *tsk;
+
+                       io_sq_thread_park(sqd);
+                       tsk = sqd->thread;
+                       if (tsk && tsk->io_uring && tsk->io_uring->io_wq)
+                               io_wq_cancel_cb(tsk->io_uring->io_wq,
+                                               io_cancel_ctx_cb, ctx, true);
+                       io_sq_thread_unpark(sqd);
+               }
 
                WARN_ON_ONCE(time_after(jiffies, timeout));
        } while (!wait_for_completion_timeout(&ctx->ref_comp, HZ/20));
@@ -8844,13 +8862,6 @@ static bool io_cancel_defer_files(struct io_ring_ctx *ctx,
        return true;
 }
 
-static bool io_cancel_ctx_cb(struct io_wq_work *work, void *data)
-{
-       struct io_kiocb *req = container_of(work, struct io_kiocb, work);
-
-       return req->ctx == data;
-}
-
 static bool io_uring_try_cancel_iowq(struct io_ring_ctx *ctx)
 {
        struct io_tctx_node *node;