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From: Christoph Hellwig <hch@lst.de>
To: viro@zeniv.linux.org.uk
Cc: Avi Kivity <avi@scylladb.com>,
	linux-aio@kvack.org, linux-fsdevel@vger.kernel.org,
	netdev@vger.kernel.org, linux-api@vger.kernel.org,
	linux-kernel@vger.kernel.org
Subject: [PATCH 05/36] aio: simplify cancellation
Date: Wed, 17 Jan 2018 20:27:11 +0100	[thread overview]
Message-ID: <20180117192742.710-6-hch@lst.de> (raw)
In-Reply-To: <20180117192742.710-1-hch@lst.de>

With the current aio code there is no need for the magic KIOCB_CANCELLED
value, as a cancelation just kicks the driver to queue the completion
ASAP, with all actual completion handling done in another thread. Given
that both the completion path and cancelation take the context lock there
is no need for magic cmpxchg loops either.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Acked-by: Jeff Moyer <jmoyer@redhat.com>
---
 fs/aio.c | 37 +++++++++----------------------------
 1 file changed, 9 insertions(+), 28 deletions(-)

diff --git a/fs/aio.c b/fs/aio.c
index c32c315f05b5..2d40cf5dd4ec 100644
--- a/fs/aio.c
+++ b/fs/aio.c
@@ -156,19 +156,6 @@ struct kioctx {
 	unsigned		id;
 };
 
-/*
- * We use ki_cancel == KIOCB_CANCELLED to indicate that a kiocb has been either
- * cancelled or completed (this makes a certain amount of sense because
- * successful cancellation - io_cancel() - does deliver the completion to
- * userspace).
- *
- * And since most things don't implement kiocb cancellation and we'd really like
- * kiocb completion to be lockless when possible, we use ki_cancel to
- * synchronize cancellation and completion - we only set it to KIOCB_CANCELLED
- * with xchg() or cmpxchg(), see batch_complete_aio() and kiocb_cancel().
- */
-#define KIOCB_CANCELLED		((void *) (~0ULL))
-
 struct aio_kiocb {
 	union {
 		struct kiocb		rw;
@@ -565,24 +552,18 @@ void kiocb_set_cancel_fn(struct kiocb *iocb, kiocb_cancel_fn *cancel)
 }
 EXPORT_SYMBOL(kiocb_set_cancel_fn);
 
+/*
+ * Only cancel if there ws a ki_cancel function to start with, and we
+ * are the one how managed to clear it (to protect against simulatinious
+ * cancel calls).
+ */
 static int kiocb_cancel(struct aio_kiocb *kiocb)
 {
-	kiocb_cancel_fn *old, *cancel;
-
-	/*
-	 * Don't want to set kiocb->ki_cancel = KIOCB_CANCELLED unless it
-	 * actually has a cancel function, hence the cmpxchg()
-	 */
-
-	cancel = READ_ONCE(kiocb->ki_cancel);
-	do {
-		if (!cancel || cancel == KIOCB_CANCELLED)
-			return -EINVAL;
-
-		old = cancel;
-		cancel = cmpxchg(&kiocb->ki_cancel, old, KIOCB_CANCELLED);
-	} while (cancel != old);
+	kiocb_cancel_fn *cancel = kiocb->ki_cancel;
 
+	if (!cancel)
+		return -EINVAL;
+	kiocb->ki_cancel = NULL;
 	return cancel(&kiocb->rw);
 }
 
-- 
2.14.2

  parent reply	other threads:[~2018-01-17 19:27 UTC|newest]

Thread overview: 49+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-01-17 19:27 aio poll, io_pgetevents and a new in-kernel poll API V3 Christoph Hellwig
2018-01-17 19:27 ` [PATCH 01/36] aio: don't print the page size at boot time Christoph Hellwig
2018-01-17 19:27 ` [PATCH 02/36] aio: remove an outdated comment in aio_complete Christoph Hellwig
2018-01-17 19:27 ` [PATCH 03/36] aio: refactor read/write iocb setup Christoph Hellwig
2018-01-17 19:27 ` [PATCH 04/36] aio: sanitize ki_list handling Christoph Hellwig
2018-01-17 19:27 ` Christoph Hellwig [this message]
2018-01-17 19:27 ` [PATCH 06/36] aio: delete iocbs from the active_reqs list in kiocb_cancel Christoph Hellwig
2018-01-17 19:27 ` [PATCH 07/36] aio: add delayed cancel support Christoph Hellwig
2018-01-17 19:27 ` [PATCH 08/36] aio: implement io_pgetevents Christoph Hellwig
2018-01-17 19:27 ` [PATCH 09/36] fs: unexport poll_schedule_timeout Christoph Hellwig
2018-01-17 19:27 ` [PATCH 10/36] fs: cleanup do_pollfd Christoph Hellwig
2018-01-17 19:27 ` [PATCH 11/36] fs: update documentation for __poll_t Christoph Hellwig
2018-01-17 19:27 ` [PATCH 12/36] fs: add new vfs_poll and file_can_poll helpers Christoph Hellwig
2018-01-17 19:27 ` [PATCH 13/36] fs: introduce new ->get_poll_head and ->poll_mask methods Christoph Hellwig
2018-01-17 19:27 ` [PATCH 14/36] aio: implement IOCB_CMD_POLL Christoph Hellwig
2018-01-17 19:27 ` [PATCH 15/36] net: refactor socket_poll Christoph Hellwig
2018-01-17 19:27 ` [PATCH 16/36] net: add support for ->poll_mask in proto_ops Christoph Hellwig
2018-01-17 19:27 ` [PATCH 17/36] net: remove sock_no_poll Christoph Hellwig
2018-01-17 19:27 ` [PATCH 18/36] net/tcp: convert to ->poll_mask Christoph Hellwig
2018-01-17 19:27 ` [PATCH 19/36] net/unix: " Christoph Hellwig
2018-01-17 19:27 ` [PATCH 20/36] net: convert datagram_poll users tp ->poll_mask Christoph Hellwig
2018-01-17 19:27 ` [PATCH 21/36] net/dccp: convert to ->poll_mask Christoph Hellwig
2018-01-17 19:27 ` [PATCH 22/36] net/atm: " Christoph Hellwig
2018-01-17 19:27 ` [PATCH 23/36] net/vmw_vsock: " Christoph Hellwig
2018-01-17 19:27 ` [PATCH 24/36] net/tipc: " Christoph Hellwig
2018-01-17 19:27 ` [PATCH 25/36] net/sctp: " Christoph Hellwig
2018-01-17 19:27 ` [PATCH 26/36] net/bluetooth: " Christoph Hellwig
2018-01-17 19:27 ` [PATCH 27/36] net/caif: " Christoph Hellwig
2018-01-17 19:27 ` [PATCH 28/36] net/nfc: " Christoph Hellwig
2018-01-17 19:27 ` [PATCH 29/36] net/phonet: " Christoph Hellwig
2018-01-17 19:27 ` [PATCH 30/36] net/iucv: " Christoph Hellwig
2018-01-17 19:27 ` [PATCH 31/36] net/rxrpc: " Christoph Hellwig
2018-01-17 19:27 ` [PATCH 32/36] crypto: af_alg: " Christoph Hellwig
2018-01-17 19:27 ` [PATCH 33/36] pipe: " Christoph Hellwig
2018-01-17 19:27 ` [PATCH 34/36] eventfd: switch " Christoph Hellwig
2018-01-17 19:27 ` [PATCH 35/36] timerfd: convert " Christoph Hellwig
2018-01-17 19:27 ` [PATCH 36/36] random: " Christoph Hellwig
2018-01-18 15:46 ` aio poll, io_pgetevents and a new in-kernel poll API V3 Jeff Moyer
2018-01-18 16:44   ` Jeff Moyer
2018-01-18 17:42     ` Christoph Hellwig
2018-01-18 17:59       ` Jeff Moyer
2018-01-18 17:55     ` Colin Walters
2018-01-18 18:53       ` Christoph Hellwig
2018-01-18 17:51   ` Avi Kivity
2018-01-18 17:52     ` Avi Kivity
2018-01-18 17:54     ` Jeff Moyer
2018-01-22 20:12 aio poll, io_pgetevents and a new in-kernel poll API V4 Christoph Hellwig
2018-01-22 20:12 ` [PATCH 05/36] aio: simplify cancellation Christoph Hellwig
2018-03-05 21:27 aio poll, io_pgetevents and a new in-kernel poll API V5 Christoph Hellwig
2018-03-05 21:27 ` [PATCH 05/36] aio: simplify cancellation Christoph Hellwig
2018-03-20  0:25   ` Darrick J. Wong

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