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Date: Tue, 2 Apr 2013 15:53:03 -0400
From: "Theodore Ts'o" <tytso@mit.edu>
To: Kent Overstreet <koverstreet@google.com>
Cc: linux-kernel@vger.kernel.org, linux-aio@kvack.org,
        akpm@linux-foundation.org, Zach Brown <zab@redhat.com>,
        Felipe Balbi <balbi@ti.com>,
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        Jeff Moyer <jmoyer@redhat.com>, Al Viro <viro@zeniv.linux.org.uk>,
        Benjamin LaHaise <bcrl@kvack.org>, Minchan Kim <minchan@kernel.org>
Subject: Re: [PATCH 30/33] block, aio: batch completion for bios/kiocbs
Message-ID: <20130402195303.GB5703@thunk.org>
Mail-Followup-To: Theodore Ts'o <tytso@mit.edu>,
	Kent Overstreet <koverstreet@google.com>,
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	Rusty Russell <rusty@rustcorp.com.au>, Jens Axboe <axboe@kernel.dk>,
	Asai Thambi S P <asamymuthupa@micron.com>,
	Selvan Mani <smani@micron.com>, Sam Bradshaw <sbradshaw@micron.com>,
	Jeff Moyer <jmoyer@redhat.com>, Al Viro <viro@zeniv.linux.org.uk>,
	Benjamin LaHaise <bcrl@kvack.org>, Minchan Kim <minchan@kernel.org>
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On Thu, Mar 21, 2013 at 09:35:51AM -0700, Kent Overstreet wrote:
> +		if (unlikely(req->ki_eventfd != eventfd)) {
> +			if (eventfd) {
> +				/* Make event visible */
> +				kioctx_ring_unlock(ctx, tail);
> +				ctx = NULL;
> +
> +				eventfd_signal(eventfd, 1);
> +				eventfd_ctx_put(eventfd);
> +			}

I just noticed something else.  There's a ring unlock here().... but
there isn't a matching ring_lock(), or an exit from the function.
Since you've set the ctx to be NULL, then subsequently, aren't we
going to crash at the subseqent kioctx_ring_unlock() below....

> +
> +			eventfd = req->ki_eventfd;
> +			req->ki_eventfd = NULL;
> +		}
> +
> +		if (unlikely(req->ki_ctx != ctx)) {
> +			kioctx_ring_unlock(ctx, tail);
                        ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

(Or the kioctx_ring_unlock() at the end of this function after the
while loop terminates.)

						- Ted

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