[PATCH] aio_run_iocb should always retry

When an AIO operation is cancelled, the ki_cancel callback can't
determine whether the ki_retry callback will ever be called. As a
result, it can't correctly determine whether to free resources. This
patch changes aio_run_iocb to always call ki_retry.

Signed-off-by: Sarah Sharp <[email protected]>
Signed-off-by: Jamey Sharp <[email protected]>
---

I've been using gadgetfs (the USB slave filesystem) as an example for
how to do in-kernel AIO.  Both gadgetfs and usbfs2 use callbacks from
the USB core to know when data is transfered.  If the transfer was a
write, the completion function simply calls aio_complete() and frees
data structures.  If it's a read, the completion function function calls
kick_iocb().  The retry function copies data into userspace, calls
aio_complete(), and then frees the data structures.

The problem comes when someone calls sys_io_cancel() on a read.  If the
retry function has started before this point, everything is fine.
However, if sys_io_cancel() runs before the retry function, aio_run_iocb
will notice the iocb is cancelled and call aio_complete instead.  The
retry function never runs, and the data structures are never freed.

Jamey and I believe there is no way to know in the cancel function if
the retry function will be called.  Therefore, kick_iocb() should always
call the retry function.  This patch fixes that bug.

I'd love to ditch the in-kernel AIO and use syslets instead, but Greg
won't accept my usbfs2 patches until I've implemented AIO, and I don't
want to keep waiting.

Sarah Sharp

 fs/aio.c |    8 --------
 1 files changed, 0 insertions(+), 8 deletions(-)

diff --git a/fs/aio.c b/fs/aio.c
index dbe699e..439c0a7 100644
--- a/fs/aio.c
+++ b/fs/aio.c
@@ -700,14 +700,6 @@ static ssize_t aio_run_iocb(struct kiocb *iocb)
 	iocb->ki_run_list.next = iocb->ki_run_list.prev = NULL;
 	spin_unlock_irq(&ctx->ctx_lock);
 
-	/* Quit retrying if the i/o has been cancelled */
-	if (kiocbIsCancelled(iocb)) {
-		ret = -EINTR;
-		aio_complete(iocb, ret, 0);
-		/* must not access the iocb after this */
-		goto out;
-	}
-
 	/*
 	 * Now we are all set to call the retry method in async
 	 * context. By setting this thread's io_wait context
-- 
1.4.4.1


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