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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 07/32] aio: simplify cancellation
Date: Tue, 15 May 2018 21:48:08 +0200	[thread overview]
Message-ID: <20180515194833.6906-8-hch@lst.de> (raw)
In-Reply-To: <20180515194833.6906-1-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 before calling ->ki_cancel 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 | 49 ++++++-------------------------------------------
 1 file changed, 6 insertions(+), 43 deletions(-)

diff --git a/fs/aio.c b/fs/aio.c
index 2e0bc04f7920..8991baa38d5d 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
@@ -641,9 +607,8 @@ 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);
-
 		list_del_init(&req->ki_list);
-		kiocb_cancel(req);
+		req->ki_cancel(&req->rw);
 	}
 
 	spin_unlock_irq(&ctx->ctx_lock);
@@ -1843,8 +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;
@@ -1856,13 +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) {
+		list_del_init(&kiocb->ki_list);
+		ret = kiocb->ki_cancel(&kiocb->rw);
+	}
 	spin_unlock_irq(&ctx->ctx_lock);
 
 	if (!ret) {
-- 
2.17.0

  parent reply	other threads:[~2018-05-15 19:49 UTC|newest]

Thread overview: 39+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-05-15 19:48 aio poll and a new in-kernel poll API V11 Christoph Hellwig
2018-05-15 19:48 ` [PATCH 01/32] fs: unexport poll_schedule_timeout Christoph Hellwig
2018-05-15 19:48 ` [PATCH 02/32] fs: cleanup do_pollfd Christoph Hellwig
2018-05-15 19:48 ` [PATCH 03/32] fs: update documentation to mention __poll_t and match the code Christoph Hellwig
2018-05-15 19:48 ` [PATCH 04/32] fs: add new vfs_poll and file_can_poll helpers Christoph Hellwig
2018-05-15 19:48 ` [PATCH 05/32] fs: introduce new ->get_poll_head and ->poll_mask methods Christoph Hellwig
2018-05-15 19:48 ` [PATCH 06/32] aio: simplify KIOCB_KEY handling Christoph Hellwig
2018-05-15 19:48 ` Christoph Hellwig [this message]
2018-05-15 19:48 ` [PATCH 08/32] aio: replace kiocb_set_cancel_fn with a cancel_kiocb file operation Christoph Hellwig
2018-05-20  5:27   ` Al Viro
2018-05-15 19:48 ` [PATCH 09/32] aio: add delayed cancel support Christoph Hellwig
2018-05-15 19:48 ` [PATCH 10/32] aio: implement IOCB_CMD_POLL Christoph Hellwig
2018-05-20  5:32   ` Al Viro
2018-05-20  7:33     ` Al Viro
2018-05-20 17:32       ` Christoph Hellwig
2018-05-15 19:48 ` [PATCH 11/32] net: refactor socket_poll Christoph Hellwig
2018-05-15 19:48 ` [PATCH 12/32] net: add support for ->poll_mask in proto_ops Christoph Hellwig
2018-05-15 19:48 ` [PATCH 13/32] net: remove sock_no_poll Christoph Hellwig
2018-05-15 19:48 ` [PATCH 14/32] net/tcp: convert to ->poll_mask Christoph Hellwig
2018-05-15 19:48 ` [PATCH 15/32] net/unix: " Christoph Hellwig
2018-05-15 19:48 ` [PATCH 16/32] net: convert datagram_poll users tp ->poll_mask Christoph Hellwig
2018-05-15 19:48 ` [PATCH 17/32] net/dccp: convert to ->poll_mask Christoph Hellwig
2018-05-15 19:48 ` [PATCH 18/32] net/atm: " Christoph Hellwig
2018-05-15 19:48 ` [PATCH 19/32] net/vmw_vsock: " Christoph Hellwig
2018-05-15 19:48 ` [PATCH 20/32] net/tipc: " Christoph Hellwig
2018-05-15 19:48 ` [PATCH 21/32] net/sctp: " Christoph Hellwig
2018-05-15 19:48 ` [PATCH 22/32] net/bluetooth: " Christoph Hellwig
2018-05-15 19:48 ` [PATCH 23/32] net/caif: " Christoph Hellwig
2018-05-15 19:48 ` [PATCH 24/32] net/nfc: " Christoph Hellwig
2018-05-15 19:48 ` [PATCH 25/32] net/phonet: " Christoph Hellwig
2018-05-15 19:48 ` [PATCH 26/32] net/iucv: " Christoph Hellwig
2018-05-15 19:48 ` [PATCH 27/32] net/rxrpc: " Christoph Hellwig
2018-05-15 19:48 ` [PATCH 28/32] crypto: af_alg: " Christoph Hellwig
2018-05-15 19:48 ` [PATCH 29/32] pipe: " Christoph Hellwig
2018-05-15 19:48 ` [PATCH 30/32] eventfd: switch " Christoph Hellwig
2018-05-15 19:48 ` [PATCH 31/32] timerfd: convert " Christoph Hellwig
2018-05-15 19:48 ` [PATCH 32/32] random: " Christoph Hellwig
  -- strict thread matches above, loose matches on Subject: below --
2018-05-11 11:07 aio poll and a new in-kernel poll API V10 Christoph Hellwig
2018-05-11 11:07 ` [PATCH 07/32] aio: simplify cancellation Christoph Hellwig
2018-03-30 15:07 aio poll and a new in-kernel poll API V9 Christoph Hellwig
2018-03-30 15:07 ` [PATCH 07/32] aio: simplify cancellation Christoph Hellwig

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