From: Stefan Hajnoczi <stefanha@redhat.com>

Date: Mon, 11 May 2020 19:36:29 +0100

Subject: [PATCH] aio-posix: don't duplicate fd handler deletion in

 fdmon_io_uring_destroy()

The io_uring file descriptor monitoring implementation has an internal

list of fd handlers that are pending submission to io_uring.

fdmon_io_uring_destroy() deletes all fd handlers on the list.

Don't delete fd handlers directly in fdmon_io_uring_destroy() for two

reasons:

1. This duplicates the aio-posix.c AioHandler deletion code and could

   become outdated if the struct changes.

2. Only handlers with the FDMON_IO_URING_REMOVE flag set are safe to

   remove. If the flag is not set then something still has a pointer to

   the fd handler. Let aio-posix.c and its user worry about that. In

   practice this isn't an issue because fdmon_io_uring_destroy() is only

   called when shutting down so all users have removed their fd

   handlers, but the next patch will need this!

Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>

---

 util/aio-posix.c      |  1 +

 util/fdmon-io_uring.c | 13 ++++++++++---

 2 files changed, 11 insertions(+), 3 deletions(-)

diff --git a/util/aio-posix.c b/util/aio-posix.c

index c3613d299e..8af334ab19 100644

--- a/util/aio-posix.c

+++ b/util/aio-posix.c

@@ -679,6 +679,7 @@ void aio_context_destroy(AioContext *ctx)

 {

     fdmon_io_uring_destroy(ctx);

     fdmon_epoll_disable(ctx);

+    aio_free_deleted_handlers(ctx);

 }

 void aio_context_set_poll_params(AioContext *ctx, int64_t max_ns,

diff --git a/util/fdmon-io_uring.c b/util/fdmon-io_uring.c

index d5a80ed6fb..1d14177df0 100644

--- a/util/fdmon-io_uring.c

+++ b/util/fdmon-io_uring.c

@@ -342,11 +342,18 @@ void fdmon_io_uring_destroy(AioContext *ctx)

         io_uring_queue_exit(&ctx->fdmon_io_uring);

-        /* No need to submit these anymore, just free them. */

+        /* Move handlers due to be removed onto the deleted list */

         while ((node = QSLIST_FIRST_RCU(&ctx->submit_list))) {

+            unsigned flags = atomic_fetch_and(&node->flags,

+                    ~(FDMON_IO_URING_PENDING |

+                      FDMON_IO_URING_ADD |

+                      FDMON_IO_URING_REMOVE));

+

+            if (flags & FDMON_IO_URING_REMOVE) {

+                QLIST_INSERT_HEAD_RCU(&ctx->deleted_aio_handlers, node, node_deleted);

+            }

+

             QSLIST_REMOVE_HEAD_RCU(&ctx->submit_list, node_submitted);

-            QLIST_REMOVE(node, node);

-            g_free(node);

         }

         ctx->fdmon_ops = &fdmon_poll_ops;