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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 09/33] aio: simplify cancellation
Date: Wed, 23 May 2018 21:19:58 +0200	[thread overview]
Message-ID: <20180523192022.1703-10-hch@lst.de> (raw)
In-Reply-To: <20180523192022.1703-1-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.  If we remove iocbs from the
active list after calling ->ki_cancel (but with ctx_lock still held), we
can also rely on the invariant thay anything found on the list has a
->ki_cancel callback and can be cancelled, further simplifing the code.

Signed-off-by: Christoph Hellwig <hch@lst.de>
---
 fs/aio.c | 48 ++++++------------------------------------------
 1 file changed, 6 insertions(+), 42 deletions(-)

diff --git a/fs/aio.c b/fs/aio.c
index 50a90e5581ed..0633cf3b325c 100644
--- a/fs/aio.c
+++ b/fs/aio.c
@@ -164,19 +164,6 @@ struct fsync_iocb {
 	bool			datasync;
 };
 
-/*
- * 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;
@@ -574,27 +561,6 @@ void kiocb_set_cancel_fn(struct kiocb *iocb, kiocb_cancel_fn *cancel)
 }
 EXPORT_SYMBOL(kiocb_set_cancel_fn);
 
-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);
-
-	return cancel(&kiocb->rw);
-}
-
 /*
  * free_ioctx() should be RCU delayed to synchronize against the RCU
  * protected lookup_ioctx() and also needs process context to call
@@ -641,7 +607,7 @@ static void free_ioctx_users(struct percpu_ref *ref)
 	while (!list_empty(&ctx->active_reqs)) {
 		req = list_first_entry(&ctx->active_reqs,
 				       struct aio_kiocb, ki_list);
-		kiocb_cancel(req);
+		req->ki_cancel(&req->rw);
 		list_del_init(&req->ki_list);
 	}
 
@@ -1842,8 +1808,8 @@ SYSCALL_DEFINE3(io_cancel, aio_context_t, ctx_id, struct iocb __user *, iocb,
 {
 	struct kioctx *ctx;
 	struct aio_kiocb *kiocb;
+	int ret = -EINVAL;
 	u32 key;
-	int ret;
 
 	if (unlikely(get_user(key, &iocb->aio_key)))
 		return -EFAULT;
@@ -1855,13 +1821,11 @@ SYSCALL_DEFINE3(io_cancel, aio_context_t, ctx_id, struct iocb __user *, iocb,
 		return -EINVAL;
 
 	spin_lock_irq(&ctx->ctx_lock);
-
 	kiocb = lookup_kiocb(ctx, iocb);
-	if (kiocb)
-		ret = kiocb_cancel(kiocb);
-	else
-		ret = -EINVAL;
-
+	if (kiocb) {
+		ret = kiocb->ki_cancel(&kiocb->rw);
+		list_del_init(&kiocb->ki_list);
+	}
 	spin_unlock_irq(&ctx->ctx_lock);
 
 	if (!ret) {
-- 
2.17.0

  parent reply	other threads:[~2018-05-23 19:20 UTC|newest]

Thread overview: 72+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-05-23 19:19 aio poll and a new in-kernel poll API V13 Christoph Hellwig
2018-05-23 19:19 ` [PATCH 01/33] fix io_destroy()/aio_complete() race Christoph Hellwig
2018-05-23 19:19 ` [PATCH 02/33] uapi: turn __poll_t sparse checkin on by default Christoph Hellwig
2018-05-23 19:19 ` [PATCH 03/33] fs: unexport poll_schedule_timeout Christoph Hellwig
2018-05-23 19:19 ` [PATCH 04/33] fs: cleanup do_pollfd Christoph Hellwig
2018-05-23 19:19 ` [PATCH 05/33] fs: update documentation to mention __poll_t and match the code Christoph Hellwig
2018-05-23 19:19 ` [PATCH 06/33] fs: add new vfs_poll and file_can_poll helpers Christoph Hellwig
2018-05-23 19:19 ` [PATCH 07/33] fs: introduce new ->get_poll_head and ->poll_mask methods Christoph Hellwig
2018-05-23 19:19 ` [PATCH 08/33] aio: simplify KIOCB_KEY handling Christoph Hellwig
2018-05-23 19:19 ` Christoph Hellwig [this message]
2018-05-23 19:19 ` [PATCH 10/33] aio: implement IOCB_CMD_POLL Christoph Hellwig
2018-05-23 19:20 ` [PATCH 11/33] aio: try to complete poll iocbs without context switch Christoph Hellwig
2018-05-23 19:20 ` [PATCH 12/33] net: refactor socket_poll Christoph Hellwig
2018-05-23 19:20 ` [PATCH 13/33] net: add support for ->poll_mask in proto_ops Christoph Hellwig
2018-05-23 19:20 ` [PATCH 14/33] net: remove sock_no_poll Christoph Hellwig
2018-05-23 19:20 ` [PATCH 15/33] net/tcp: convert to ->poll_mask Christoph Hellwig
2018-05-23 19:20 ` [PATCH 16/33] net/unix: " Christoph Hellwig
2018-05-23 19:20 ` [PATCH 17/33] net: convert datagram_poll users tp ->poll_mask Christoph Hellwig
2018-05-23 19:20 ` [PATCH 18/33] net/dccp: convert to ->poll_mask Christoph Hellwig
2018-05-23 19:20 ` [PATCH 19/33] net/atm: " Christoph Hellwig
2018-05-23 19:20 ` [PATCH 20/33] net/vmw_vsock: " Christoph Hellwig
2018-05-23 19:20 ` [PATCH 21/33] net/tipc: " Christoph Hellwig
2018-05-23 19:20 ` [PATCH 22/33] net/sctp: " Christoph Hellwig
2018-05-23 19:20 ` [PATCH 23/33] net/bluetooth: " Christoph Hellwig
2018-05-23 19:20 ` [PATCH 24/33] net/caif: " Christoph Hellwig
2018-05-23 19:20 ` [PATCH 25/33] net/nfc: " Christoph Hellwig
2018-05-23 19:20 ` [PATCH 26/33] net/phonet: " Christoph Hellwig
2018-05-23 19:20 ` [PATCH 27/33] net/iucv: " Christoph Hellwig
2018-05-23 19:20 ` [PATCH 28/33] net/rxrpc: " Christoph Hellwig
2018-05-23 19:20 ` [PATCH 29/33] crypto: af_alg: " Christoph Hellwig
2018-05-23 19:20 ` [PATCH 30/33] pipe: " Christoph Hellwig
2018-05-23 19:20 ` [PATCH 31/33] eventfd: switch " Christoph Hellwig
2018-05-23 19:20 ` [PATCH 32/33] timerfd: convert " Christoph Hellwig
2018-05-23 19:20 ` [PATCH 33/33] random: " Christoph Hellwig
2018-05-26  0:11 ` aio poll and a new in-kernel poll API V13 Al Viro
2018-05-26  7:09   ` Al Viro
2018-05-26  7:23     ` Christoph Hellwig
2018-05-27 22:27       ` Al Viro
2018-05-27 22:28         ` [PATCH 1/4] aio: all callers of aio_{read,write,fsync,poll} treat 0 and -EIOCBQUEUED the same way Al Viro
2018-05-27 22:28           ` [PATCH 2/4] aio_read_events_ring(): make a bit more readable Al Viro
2018-05-27 22:28           ` [PATCH 3/4] aio: shift copyin of iocb into io_submit_one() Al Viro
2018-05-28  5:16             ` Christoph Hellwig
2018-05-27 22:28           ` [PATCH 4/4] aio: fold do_io_submit() into callers Al Viro
2018-05-27 23:14             ` Al Viro
2018-05-28  5:24               ` Christoph Hellwig
2018-05-28  5:15           ` [PATCH 1/4] aio: all callers of aio_{read,write,fsync,poll} treat 0 and -EIOCBQUEUED the same way Christoph Hellwig
2018-05-28 14:04             ` Al Viro
2018-05-28 17:54               ` Al Viro
2018-05-28 17:57                 ` [PATCH v2 1/6] aio: take list removal to (some) callers of aio_complete() Al Viro
2018-05-28 17:57                   ` [PATCH v2 2/6] aio: all callers of aio_{read,write,fsync,poll} treat 0 and -EIOCBQUEUED the same way Al Viro
2018-05-29  6:08                     ` Christoph Hellwig
2018-05-28 17:57                   ` [PATCH v2 3/6] aio_read_events_ring(): make a bit more readable Al Viro
2018-05-28 17:57                   ` [PATCH v2 4/6] aio: shift copyin of iocb into io_submit_one() Al Viro
2018-05-28 17:57                   ` [PATCH v2 5/6] aio: fold do_io_submit() into callers Al Viro
2018-05-29  6:10                     ` Christoph Hellwig
2018-05-28 17:57                   ` [PATCH v2 6/6] aio: sanitize the limit checking in io_submit(2) Al Viro
2018-05-29  6:10                     ` Christoph Hellwig
2018-05-29  6:08                   ` [PATCH v2 1/6] aio: take list removal to (some) callers of aio_complete() Christoph Hellwig
2018-05-28 22:20                 ` [PATCH 1/4] vmsplice: lift import_iovec() into do_vmsplice() Al Viro
2018-05-28 22:20                   ` [PATCH 2/4] vmsplice(): lift importing iovec into vmsplice(2) and compat counterpart Al Viro
2018-05-28 22:20                   ` [PATCH 3/4] signalfd: lift sigmask copyin and size checks to callers of do_signalfd4() Al Viro
2018-05-28 22:20                   ` [PATCH 4/4] orangefs: simplify compat ioctl handling Al Viro
2018-05-31 11:11                     ` kbuild test robot
2018-05-31 20:54                     ` Mike Marshall
2018-05-31 21:03                       ` Al Viro
2018-06-01 21:13                         ` Mike Marshall
2018-06-06 22:57                   ` [1/4] vmsplice: lift import_iovec() into do_vmsplice() Andrei Vagin
2018-06-07 17:56                     ` Andrei Vagin
2018-06-11 20:14                       ` Cyrill Gorcunov
2018-06-11 20:16                         ` Al Viro
2018-06-11 20:18                           ` Cyrill Gorcunov
2018-06-14 22:22                           ` Andrey Vagin

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