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From: Al Viro <viro@ZenIV.linux.org.uk>
To: Christoph Hellwig <hch@lst.de>
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: Re: [PATCH 10/32] aio: implement IOCB_CMD_POLL
Date: Sun, 20 May 2018 08:33:39 +0100	[thread overview]
Message-ID: <20180520073332.GA30522@ZenIV.linux.org.uk> (raw)
In-Reply-To: <20180520053219.GZ30522@ZenIV.linux.org.uk>

On Sun, May 20, 2018 at 06:32:25AM +0100, Al Viro wrote:
> > +	spin_lock_irqsave(&ctx->ctx_lock, flags);
> > +	list_add_tail(&aiocb->ki_list, &ctx->delayed_cancel_reqs);
> > +	spin_unlock(&ctx->ctx_lock);
> 
> ... and io_cancel(2) comes, finds it and inhume^Wcompletes it, leaving us to...
> 
> > +	spin_lock(&req->head->lock);
> 
> ... get buggered on attempt to dereference a pointer fetched from freed and
> reused object.

FWIW, how painful would it be to pull the following trick:
	* insert into wait queue under ->ctx_lock
	* have wakeup do schedule_work() with aio_complete() done from that
	* have ->ki_cancel() grab queue lock, remove from queue and use
the same schedule_work()

That way you'd get ->ki_cancel() with the same semantics as originally for
everything - "ask politely to finish ASAP", and called in the same locking
environment for everyone - under ->ctx_lock, that is.  queue lock nests
inside ->ctx_lock; no magical flags, etc.

The cost is schedule_work() for each async poll-related completion as you
have for fsync.  I don't know whether that's too costly or not; it certainly
simplifies the things, but whether it's OK performance-wise...

Comments?

  reply	other threads:[~2018-05-20  7:34 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 ` [PATCH 07/32] aio: simplify cancellation Christoph Hellwig
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 [this message]
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 10/32] aio: implement IOCB_CMD_POLL 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 10/32] aio: implement IOCB_CMD_POLL Christoph Hellwig

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