On 8/11/20 12:47 AM, syzbot wrote: > Hello, > > syzbot found the following issue on: > > HEAD commit: fc80c51f Merge tag 'kbuild-v5.9' of git://git.kernel.org/p.. > git tree: upstream > console output: https://syzkaller.appspot.com/x/log.txt?x=17601ab2900000 > kernel config: https://syzkaller.appspot.com/x/.config?x=d48472fcc2f68903 > dashboard link: https://syzkaller.appspot.com/bug?extid=9b260fc33297966f5a8e > compiler: clang version 10.0.0 (https://github.com/llvm/llvm-project/ c2443155a0fb245c8f17f2c1c72b6ea391e86e81) > syz repro: https://syzkaller.appspot.com/x/repro.syz?x=174272b2900000 > > IMPORTANT: if you fix the issue, please add the following tag to the commit: > Reported-by: syzbot+9b260fc33297966f5a8e@xxxxxxxxxxxxxxxxxxxxxxxxx I think the below should fix it, for this use case and potentially others. If the ring is closed and the task_work bound req is holding the last reference, we need to hold a ctx reference around it. diff --git a/fs/io_uring.c b/fs/io_uring.c index 5488698189da..cc4bb16ff570 100644 --- a/fs/io_uring.c +++ b/fs/io_uring.c @@ -1821,8 +1821,10 @@ static void __io_req_task_submit(struct io_kiocb *req) static void io_req_task_submit(struct callback_head *cb) { struct io_kiocb *req = container_of(cb, struct io_kiocb, task_work); + struct io_ring_ctx *ctx = req->ctx; __io_req_task_submit(req); + percpu_ref_put(&ctx->refs); } static void io_req_task_queue(struct io_kiocb *req) @@ -1830,6 +1832,7 @@ static void io_req_task_queue(struct io_kiocb *req) int ret; init_task_work(&req->task_work, io_req_task_submit); + percpu_ref_get(&req->ctx->refs); ret = io_req_task_work_add(req, &req->task_work); if (unlikely(ret)) { @@ -2318,6 +2321,8 @@ static void io_rw_resubmit(struct callback_head *cb) refcount_inc(&req->refs); io_queue_async_work(req); } + + percpu_ref_put(&ctx->refs); } #endif @@ -2330,6 +2335,8 @@ static bool io_rw_reissue(struct io_kiocb *req, long res) return false; init_task_work(&req->task_work, io_rw_resubmit); + percpu_ref_get(&req->ctx->refs); + ret = io_req_task_work_add(req, &req->task_work); if (!ret) return true; @@ -3033,6 +3040,8 @@ static int io_async_buf_func(struct wait_queue_entry *wait, unsigned mode, list_del_init(&wait->entry); init_task_work(&req->task_work, io_req_task_submit); + percpu_ref_get(&req->ctx->refs); + /* submit ref gets dropped, acquire a new one */ refcount_inc(&req->refs); ret = io_req_task_work_add(req, &req->task_work); @@ -4565,6 +4574,8 @@ static int __io_async_wake(struct io_kiocb *req, struct io_poll_iocb *poll, req->result = mask; init_task_work(&req->task_work, func); + percpu_ref_get(&req->ctx->refs); + /* * If this fails, then the task is exiting. When a task exits, the * work gets canceled, so just cancel this request as well instead @@ -4652,11 +4663,13 @@ static void io_poll_task_handler(struct io_kiocb *req, struct io_kiocb **nxt) static void io_poll_task_func(struct callback_head *cb) { struct io_kiocb *req = container_of(cb, struct io_kiocb, task_work); + struct io_ring_ctx *ctx = req->ctx; struct io_kiocb *nxt = NULL; io_poll_task_handler(req, &nxt); if (nxt) __io_req_task_submit(nxt); + percpu_ref_put(&ctx->refs); } static int io_poll_double_wake(struct wait_queue_entry *wait, unsigned mode, @@ -4752,6 +4765,7 @@ static void io_async_task_func(struct callback_head *cb) if (io_poll_rewait(req, &apoll->poll)) { spin_unlock_irq(&ctx->completion_lock); + percpu_ref_put(&ctx->refs); return; } -- Jens Axboe
