linux-kernel - Re: [PATCH 12/33] aio: refcounting cleanup

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Message-ID: <20130402013214.GA30122@thunk.org>
Date:	Mon, 1 Apr 2013 21:32:14 -0400
From:	Theodore Ts'o <tytso@....edu>
To:	Kent Overstreet <koverstreet@...gle.com>
Cc:	linux-kernel@...r.kernel.org, linux-aio@...ck.org,
	akpm@...ux-foundation.org, Zach Brown <zab@...hat.com>,
	Felipe Balbi <balbi@...com>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Mark Fasheh <mfasheh@...e.com>,
	Joel Becker <jlbec@...lplan.org>,
	Rusty Russell <rusty@...tcorp.com.au>,
	Jens Axboe <axboe@...nel.dk>,
	Asai Thambi S P <asamymuthupa@...ron.com>,
	Selvan Mani <smani@...ron.com>,
	Sam Bradshaw <sbradshaw@...ron.com>,
	Jeff Moyer <jmoyer@...hat.com>,
	Al Viro <viro@...iv.linux.org.uk>,
	Benjamin LaHaise <bcrl@...ck.org>
Subject: Re: [PATCH 12/33] aio: refcounting cleanup

On Thu, Mar 21, 2013 at 09:35:33AM -0700, Kent Overstreet wrote:
> The usage of ctx->dead was fubar - it makes no sense to explicitly check
> it all over the place, especially when we're already using RCU.
> 
> Now, ctx->dead only indicates whether we've dropped the initial
> refcount. The new teardown sequence is:
> set ctx->dead
> hlist_del_rcu();
> synchronize_rcu();
> 
> Now we know no system calls can take a new ref, and it's safe to drop
> the initial ref:
> put_ioctx();
> 
> We also need to ensure there are no more outstanding kiocbs.  This was
> done incorrectly - it was being done in kill_ctx(), and before dropping
> the initial refcount.  At this point, other syscalls may still be
> submitting kiocbs!
> 
> Now, we cancel and wait for outstanding kiocbs in free_ioctx(), after
> kioctx->users has dropped to 0 and we know no more iocbs could be
> submitted.
> 
> Signed-off-by: Kent Overstreet <koverstreet@...gle.com>
> Cc: Zach Brown <zab@...hat.com>
> Cc: Felipe Balbi <balbi@...com>
> Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
> Cc: Mark Fasheh <mfasheh@...e.com>
> Cc: Joel Becker <jlbec@...lplan.org>
> Cc: Rusty Russell <rusty@...tcorp.com.au>
> Cc: Jens Axboe <axboe@...nel.dk>
> Cc: Asai Thambi S P <asamymuthupa@...ron.com>
> Cc: Selvan Mani <smani@...ron.com>
> Cc: Sam Bradshaw <sbradshaw@...ron.com>
> Cc: Jeff Moyer <jmoyer@...hat.com>
> Cc: Al Viro <viro@...iv.linux.org.uk>
> Cc: Benjamin LaHaise <bcrl@...ck.org>
> Cc: Theodore Ts'o <tytso@....edu>
> Signed-off-by: Andrew Morton <akpm@...ux-foundation.org>

Reviewed-by: "Theodore Ts'o" <tytso@....edu>
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