[PATCH 3/8] aio_poll(): sanitize the logics after vfs_poll(), get rid of leak on error

[Al Viro]

From: Al Viro <v...@zeniv.linux.org.uk>

We want iocb_put() happening on errors, to balance the extra reference
we'd taken.  As it is, we end up with a leak.  The rules should be
        * error: iocb_put() to deal with the extra ref, return error,
let the caller do another iocb_put().
        * async: iocb_put() to deal with the extra ref, return 0.
        * no error, event present immediately: aio_poll_complete() to
report it, iocb_put() to deal with the extra ref, return 0.

Signed-off-by: Al Viro <v...@zeniv.linux.org.uk>
---
 fs/aio.c | 25 +++++++++++--------------
 1 file changed, 11 insertions(+), 14 deletions(-)

diff --git a/fs/aio.c b/fs/aio.c
index 3a8b894378e0..22b288997441 100644
--- a/fs/aio.c
+++ b/fs/aio.c
@@ -1724,6 +1724,7 @@ static ssize_t aio_poll(struct aio_kiocb *aiocb, const 
struct iocb *iocb)
        struct kioctx *ctx = aiocb->ki_ctx;
        struct poll_iocb *req = &aiocb->poll;
        struct aio_poll_table apt;
+       bool async = false;
        __poll_t mask;
 
        /* reject any unknown events outside the normal event mask. */
@@ -1760,30 +1761,26 @@ static ssize_t aio_poll(struct aio_kiocb *aiocb, const 
struct iocb *iocb)
 
        spin_lock_irq(&ctx->ctx_lock);
        spin_lock(&req->head->lock);
-       if (req->woken) {
-               /* wake_up context handles the rest */
-               mask = 0;
+       if (req->woken) { /* already taken up by aio_poll_wake() */
+               async = true;
                apt.error = 0;
-       } else if (mask || apt.error) {
-               /* if we get an error or a mask we are done */
-               WARN_ON_ONCE(list_empty(&req->wait.entry));
-               list_del_init(&req->wait.entry);
-       } else {
-               /* actually waiting for an event */
+       } else if (!mask && !apt.error) { /* actually waiting for an event */
                list_add_tail(&aiocb->ki_list, &ctx->active_reqs);
                aiocb->ki_cancel = aio_poll_cancel;
+               async = true;
+       } else { /* if we get an error or a mask we are done */
+               WARN_ON_ONCE(list_empty(&req->wait.entry));
+               list_del_init(&req->wait.entry);
+               /* no wakeup in the future either; aiocb is ours to dispose of 
*/
        }
        spin_unlock(&req->head->lock);
        spin_unlock_irq(&ctx->ctx_lock);
 
 out:
-       if (unlikely(apt.error))
-               return apt.error;
-
-       if (mask)
+       if (async && !apt.error)
                aio_poll_complete(aiocb, mask);
        iocb_put(aiocb);
-       return 0;
+       return apt.error;
 }
 
 static int __io_submit_one(struct kioctx *ctx, const struct iocb *iocb,
-- 
2.11.0