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 07/30] aio: add delayed cancel support
Date: Thu, 29 Mar 2018 23:35:00 +0100 [thread overview]
Message-ID: <20180329223500.GY30522@ZenIV.linux.org.uk> (raw)
In-Reply-To: <20180329203328.3248-8-hch@lst.de>
On Thu, Mar 29, 2018 at 10:33:05PM +0200, Christoph Hellwig wrote:
> The upcoming aio poll support would like to be able to complete the
> iocb inline from the cancellation context, but that would cause a
> double lock of ctx_lock with the current locking scheme. Move the
> cancelation outside the context lock to avoid this reversal, which
> suits the existing usb gadgets users just fine as well (in fact
> both unconditionally disable irqs and thus seem broken without
> this change).
>
> To make this safe aio_complete needs to check if this call should
> complete the iocb. If it didn't the callers must not release any
> other resources.
Uh-oh... What happens to existing users of kiocb_set_cancel_fn() now?
AFAICS, those guys will *not* get aio_kiocb freed at all in case of
io_cancel(2). Look: we mark them with AIO_IOCB_CANCELLED and
call whatever ->ki_cancel() the driver has set. Later the damn
thing calls ->ki_complete() (i.e. aio_complete_rw()), which calls
aio_complete(iocb, res, res2, 0) and gets false. Nothing's freed,
struct file is leaked.
Frankly, the more I look at that, the less I like what you've done
with ->ki_cancel() overloading. In regular case it's just accelerating
the call of ->ki_complete(), which will do freeing. Here you have
->ki_cancel() free the damn thing, with the resulting need to play
silly buggers with locking, freeing logics in aio_complete(), etc.
next prev parent reply other threads:[~2018-03-29 22:35 UTC|newest]
Thread overview: 39+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-03-29 20:32 aio poll and a new in-kernel poll API V8 Christoph Hellwig
2018-03-29 20:32 ` [PATCH 01/30] fs: unexport poll_schedule_timeout Christoph Hellwig
2018-03-29 20:33 ` [PATCH 02/30] fs: cleanup do_pollfd Christoph Hellwig
2018-03-29 20:33 ` [PATCH 03/30] fs: update documentation to mention __poll_t and match the code Christoph Hellwig
2018-03-29 20:33 ` [PATCH 04/30] fs: add new vfs_poll and file_can_poll helpers Christoph Hellwig
2018-03-29 20:33 ` [PATCH 05/30] fs: introduce new ->get_poll_head and ->poll_mask methods Christoph Hellwig
2018-03-29 20:33 ` [PATCH 06/30] aio: simplify cancellation Christoph Hellwig
2018-03-29 20:33 ` [PATCH 07/30] aio: add delayed cancel support Christoph Hellwig
2018-03-29 22:35 ` Al Viro [this message]
2018-03-30 7:14 ` Christoph Hellwig
2018-03-29 20:33 ` [PATCH 08/30] aio: implement IOCB_CMD_POLL Christoph Hellwig
2018-03-29 20:33 ` [PATCH 09/30] net: refactor socket_poll Christoph Hellwig
2018-03-29 20:33 ` [PATCH 10/30] net: add support for ->poll_mask in proto_ops Christoph Hellwig
2018-03-29 20:33 ` [PATCH 11/30] net: remove sock_no_poll Christoph Hellwig
2018-03-29 20:33 ` [PATCH 12/30] net/tcp: convert to ->poll_mask Christoph Hellwig
2018-03-29 20:33 ` [PATCH 13/30] net/unix: " Christoph Hellwig
2018-03-29 20:33 ` [PATCH 14/30] net: convert datagram_poll users tp ->poll_mask Christoph Hellwig
2018-03-29 20:33 ` [PATCH 15/30] net/dccp: convert to ->poll_mask Christoph Hellwig
2018-03-29 20:33 ` [PATCH 16/30] net/atm: " Christoph Hellwig
2018-03-29 20:33 ` [PATCH 17/30] net/vmw_vsock: " Christoph Hellwig
2018-03-29 20:33 ` [PATCH 18/30] net/tipc: " Christoph Hellwig
2018-03-29 20:33 ` [PATCH 19/30] net/sctp: " Christoph Hellwig
2018-03-29 20:33 ` [PATCH 20/30] net/bluetooth: " Christoph Hellwig
2018-03-29 20:33 ` [PATCH 21/30] net/caif: " Christoph Hellwig
2018-03-29 20:33 ` [PATCH 22/30] net/nfc: " Christoph Hellwig
2018-03-29 20:33 ` [PATCH 23/30] net/phonet: " Christoph Hellwig
2018-03-29 20:33 ` [PATCH 24/30] net/iucv: " Christoph Hellwig
2018-03-29 20:33 ` [PATCH 25/30] net/rxrpc: " Christoph Hellwig
2018-03-29 20:33 ` [PATCH 26/30] crypto: af_alg: " Christoph Hellwig
2018-03-29 20:33 ` [PATCH 27/30] pipe: " Christoph Hellwig
2018-03-29 20:33 ` [PATCH 28/30] eventfd: switch " Christoph Hellwig
2018-03-29 20:33 ` [PATCH 29/30] timerfd: convert " Christoph Hellwig
2018-03-29 20:33 ` [PATCH 30/30] random: " Christoph Hellwig
-- strict thread matches above, loose matches on Subject: below --
2018-03-28 7:28 aio poll and a new in-kernel poll API V7 Christoph Hellwig
2018-03-28 7:29 ` [PATCH 07/30] aio: add delayed cancel support Christoph Hellwig
2018-03-28 16:35 ` Al Viro
2018-03-28 21:34 ` Al Viro
2018-03-29 8:53 ` Christoph Hellwig
2018-03-29 14:25 ` Al Viro
2018-03-29 18:08 ` Christoph Hellwig
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