[RFC PATCH] io_uring: stop issue failed request to fix panic

[王贇 <yun.wang@linux.alibaba.com>]

We observed panic:
  BUG: kernel NULL pointer dereference, address:0000000000000028
  [skip]
  Oops: 0000 [#1] SMP PTI
  CPU: 1 PID: 737 Comm: a.out Not tainted 5.14.0+ #58
  Hardware name: Red Hat KVM, BIOS 0.5.1 01/01/2011
  RIP: 0010:vfs_fadvise+0x1e/0x80
  [skip]
  Call Trace:
   ? tctx_task_work+0x111/0x2a0
   io_issue_sqe+0x524/0x1b90

This is caused by io_wq_submit_work() calling io_issue_sqe()
on a failed fadvise request, and the io_init_req() return error
before initialize the file for it, lead into the panic when
vfs_fadvise() try to access 'req->file'.

This patch add the missing check & handle for failed request
before calling io_issue_sqe().

Signed-off-by: Michael Wang <yun.wang@linux.alibaba.com>
---
 fs/io_uring.c | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/fs/io_uring.c b/fs/io_uring.c
index 6f35b12..bfec7bf 100644
--- a/fs/io_uring.c
+++ b/fs/io_uring.c
@@ -2214,7 +2214,8 @@ static void io_req_task_submit(struct io_kiocb *req, bool *locked)

 	io_tw_lock(ctx, locked);
 	/* req->task == current here, checking PF_EXITING is safe */
-	if (likely(!(req->task->flags & PF_EXITING)))
+	if (likely(!(req->task->flags & PF_EXITING) &&
+		   !(req->flags & REQ_F_FAIL)))
 		__io_queue_sqe(req);
 	else
 		io_req_complete_failed(req, -EFAULT);
@@ -6704,7 +6705,10 @@ static void io_wq_submit_work(struct io_wq_work *work)

 	if (!ret) {
 		do {
-			ret = io_issue_sqe(req, 0);
+			if (likely(!(req->flags & REQ_F_FAIL)))
+				ret = io_issue_sqe(req, 0);
+			else
+				io_req_complete_failed(req, -EFAULT);
 			/*
 			 * We can get EAGAIN for polled IO even though we're
 			 * forcing a sync submission from here, since we can't
-- 
1.8.3.1