aio: io_cancel() no longer returns the io_event

Originally, io_event() was documented to return the io_event if
cancellation succeeded - the io_event wouldn't be delivered via the ring
buffer like it normally would.

But this isn't what the implementation was actually doing; the only
driver implementing cancellation, the usb gadget code, never returned an
io_event in its cancel function. And aio_complete() was recently changed
to no longer suppress event delivery if the kiocb had been cancelled.

This gets rid of the unused io_event argument to kiocb_cancel() and
kiocb->ki_cancel(), and changes io_cancel() to return -EINPROGRESS if
kiocb->ki_cancel() returned success.

Also tweak the refcounting in kiocb_cancel() to make more sense.

Signed-off-by: Kent Overstreet <koverstreet@google.com>
Cc: Zach Brown <zab@redhat.com>
Cc: Felipe Balbi <balbi@ti.com>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Mark Fasheh <mfasheh@suse.com>
Cc: Joel Becker <jlbec@evilplan.org>
Cc: Rusty Russell <rusty@rustcorp.com.au>
Cc: Jens Axboe <axboe@kernel.dk>
Cc: Asai Thambi S P <asamymuthupa@micron.com>
Cc: Selvan Mani <smani@micron.com>
Cc: Sam Bradshaw <sbradshaw@micron.com>
Cc: Jeff Moyer <jmoyer@redhat.com>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: Benjamin LaHaise <bcrl@kvack.org>
Signed-off-by: Benjamin LaHaise <bcrl@kvack.org>

3 files changed, 12 insertions, 33 deletions

diff --git a/drivers/usb/gadget/inode.c b/drivers/usb/gadget/inode.c
index 570c005062ab..e02c1e04529e 100644
--- a/drivers/usb/gadget/inode.c
+++ b/drivers/usb/gadget/inode.c
@@ -524,7 +524,7 @@ struct kiocb_priv {
         unsigned                actual;
 };
 
-static int ep_aio_cancel(struct kiocb *iocb, struct io_event *e)
+static int ep_aio_cancel(struct kiocb *iocb)
 {
         struct kiocb_priv       *priv = iocb->private;
         struct ep_data          *epdata;
@@ -540,7 +540,6 @@ static int ep_aio_cancel(struct kiocb *iocb, struct io_event *e)
         // spin_unlock(&epdata->dev->lock);
         local_irq_enable();
 
-        aio_put_req(iocb);
         return value;
 }
 
diff --git a/fs/aio.c b/fs/aio.c
index 7b470bfbf891..12b37689dd2c 100644
--- a/fs/aio.c
+++ b/fs/aio.c
@@ -358,8 +358,7 @@ void kiocb_set_cancel_fn(struct kiocb *req, kiocb_cancel_fn *cancel)
 }
 EXPORT_SYMBOL(kiocb_set_cancel_fn);
 
-static int kiocb_cancel(struct kioctx *ctx, struct kiocb *kiocb,
-                        struct io_event *res)
+static int kiocb_cancel(struct kioctx *ctx, struct kiocb *kiocb)
 {
         kiocb_cancel_fn *old, *cancel;
         int ret = -EINVAL;
@@ -381,12 +380,10 @@ static int kiocb_cancel(struct kioctx *ctx, struct kiocb *kiocb,
         atomic_inc(&kiocb->ki_users);
         spin_unlock_irq(&ctx->ctx_lock);
 
-        memset(res, 0, sizeof(*res));
-        res->obj = (u64)(unsigned long)kiocb->ki_obj.user;
-        res->data = kiocb->ki_user_data;
-        ret = cancel(kiocb, res);
+        ret = cancel(kiocb);
 
         spin_lock_irq(&ctx->ctx_lock);
+        aio_put_req(kiocb);
 
         return ret;
 }
@@ -408,7 +405,6 @@ static void free_ioctx(struct work_struct *work)
 {
         struct kioctx *ctx = container_of(work, struct kioctx, free_work);
         struct aio_ring *ring;
-        struct io_event res;
         struct kiocb *req;
         unsigned cpu, head, avail;
 
@@ -419,7 +415,7 @@ static void free_ioctx(struct work_struct *work)
                                        struct kiocb, ki_list);
 
                 list_del_init(&req->ki_list);
-                kiocb_cancel(ctx, req, &res);
+                kiocb_cancel(ctx, req);
         }
 
         spin_unlock_irq(&ctx->ctx_lock);
@@ -796,21 +792,6 @@ void aio_complete(struct kiocb *iocb, long res, long res2)
         }
 
         /*
-         * cancelled requests don't get events, userland was given one
-         * when the event got cancelled.
-         */
-        if (unlikely(xchg(&iocb->ki_cancel,
-                          KIOCB_CANCELLED) == KIOCB_CANCELLED)) {
-                /*
-                 * Can't use the percpu reqs_available here - could race with
-                 * free_ioctx()
-                 */
-                atomic_inc(&ctx->reqs_available);
-                /* Still need the wake_up in case free_ioctx is waiting */
-                goto put_rq;
-        }
-
-        /*
          * Add a completion event to the ring buffer. Must be done holding
          * ctx->completion_lock to prevent other code from messing with the tail
          * pointer since we might be called from irq context.
@@ -862,7 +843,6 @@ void aio_complete(struct kiocb *iocb, long res, long res2)
         if (iocb->ki_eventfd != NULL)
                 eventfd_signal(iocb->ki_eventfd, 1);
 
-put_rq:
         /* everything turned out well, dispose of the aiocb. */
         aio_put_req(iocb);
 
@@ -1439,7 +1419,6 @@ static struct kiocb *lookup_kiocb(struct kioctx *ctx, struct iocb __user *iocb,
 SYSCALL_DEFINE3(io_cancel, aio_context_t, ctx_id, struct iocb __user *, iocb,
                 struct io_event __user *, result)
 {
-        struct io_event res;
         struct kioctx *ctx;
         struct kiocb *kiocb;
         u32 key;
@@ -1457,18 +1436,19 @@ SYSCALL_DEFINE3(io_cancel, aio_context_t, ctx_id, struct iocb __user *, iocb,
 
         kiocb = lookup_kiocb(ctx, iocb, key);
         if (kiocb)
-                ret = kiocb_cancel(ctx, kiocb, &res);
+                ret = kiocb_cancel(ctx, kiocb);
         else
                 ret = -EINVAL;
 
         spin_unlock_irq(&ctx->ctx_lock);
 
         if (!ret) {
-                /* Cancellation succeeded -- copy the result
-                 * into the user's buffer.
+                /*
+                 * The result argument is no longer used - the io_event is
+                 * always delivered via the ring buffer. -EINPROGRESS indicates
+                 * cancellation is progress:
                  */
-                if (copy_to_user(result, &res, sizeof(res)))
-                        ret = -EFAULT;
+                ret = -EINPROGRESS;
         }
 
         percpu_ref_put(&ctx->users);
diff --git a/include/linux/aio.h b/include/linux/aio.h
index 1bdf965339f9..8c8dd1d84d2e 100644
--- a/include/linux/aio.h
+++ b/include/linux/aio.h
@@ -27,7 +27,7 @@ struct kiocb;
  */
 #define KIOCB_CANCELLED         ((void *) (~0ULL))
 
-typedef int (kiocb_cancel_fn)(struct kiocb *, struct io_event *);
+typedef int (kiocb_cancel_fn)(struct kiocb *);
 
 struct kiocb {
         atomic_t                ki_users;