Re: [PATCH 2/2] io_uring: fix tw list mess-up by adding tw while it's already in tw list
From: Pavel Begunkov <asml.silence@gmail.com>
Date: 2021-09-29 11:14:23
On 9/27/21 1:36 PM, Hao Xu wrote:
For multishot mode, there may be cases like:
io_poll_task_func()
-> add_wait_queue()
async_wake()
->io_req_task_work_add()
this one mess up the running task_work list
since req->io_task_work.node is in use.By the time req->io_task_work.func() is called, node->next is undefined and free to use. io_req_task_work_add() will override it without looking at a prior value and that's fine, as the calling code doesn't touch it after the callback.
similar situation for req->io_task_work.fallback_node. Fix it by set node->next = NULL before we run the tw, so that when we add req back to the wait queue in middle of tw running, we can safely re-add it to the tw list.
I might be missing what is the problem you're trying to fix. Does the above makes sense? It doesn't sound like node->next=NULL can solve anything.
quoted hunk ↗ jump to hunk
Fixes: 7cbf1722d5fc ("io_uring: provide FIFO ordering for task_work") Signed-off-by: Hao Xu <redacted> --- fs/io_uring.c | 11 ++++++++--- 1 file changed, 8 insertions(+), 3 deletions(-)diff --git a/fs/io_uring.c b/fs/io_uring.c index d0b358b9b589..f667d6286438 100644 --- a/fs/io_uring.c +++ b/fs/io_uring.c@@ -1250,13 +1250,17 @@ static void io_fallback_req_func(struct work_struct *work) struct io_ring_ctx *ctx = container_of(work, struct io_ring_ctx, fallback_work.work); struct llist_node *node = llist_del_all(&ctx->fallback_llist); - struct io_kiocb *req, *tmp; + struct io_kiocb *req; bool locked = false; percpu_ref_get(&ctx->refs); - llist_for_each_entry_safe(req, tmp, node, io_task_work.fallback_node) + req = llist_entry(node, struct io_kiocb, io_task_work.fallback_node); + while (member_address_is_nonnull(req, io_task_work.fallback_node)) { + node = req->io_task_work.fallback_node.next; + req->io_task_work.fallback_node.next = NULL; req->io_task_work.func(req, &locked); - + req = llist_entry(node, struct io_kiocb, io_task_work.fallback_node); + } if (locked) { io_submit_flush_completions(ctx); mutex_unlock(&ctx->uring_lock);@@ -2156,6 +2160,7 @@ static void tctx_task_work(struct callback_head *cb) locked = mutex_trylock(&ctx->uring_lock); percpu_ref_get(&ctx->refs); } + node->next = NULL; req->io_task_work.func(req, &locked); node = next; } while (node);
-- Pavel Begunkov