linux-kernel - Re: [PATCH] poll/select: initialize triggered field of struct poll

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Date:	Sat, 15 Aug 2009 23:41:08 +0200 (CEST)
From:	Thomas Gleixner <tglx@...utronix.de>
To:	Guillaume Knispel <gknispel@...formatique.com>
cc:	linux-kernel@...r.kernel.org, Tejun Heo <tj@...nel.org>,
	Miklos Szeredi <mszeredi@...e.cz>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Alexander Viro <viro@...iv.linux.org.uk>,
	Arjan van de Ven <arjan@...ux.intel.com>,
	Heiko Carstens <heiko.carstens@...ibm.com>,
	linux-fsdevel@...r.kernel.org
Subject: Re: [PATCH] poll/select: initialize triggered field of struct
 poll_wqueues

Guillaume,

On Sat, 15 Aug 2009, Guillaume Knispel wrote:
> poll/select: initialize triggered field of struct poll_wqueues
> 
> The triggered field of struct poll_wqueues introduced in commit
> 5f820f648c92a5ecc771a96b3c29aa6e90013bba "poll: allow f_op->poll to
> sleep" was set to 1 in pollwake() (now __pollwake() ), tested and
> later set to 0 in poll_schedule_timeout(), but not initialized before.
> As a result when the process needs to sleep, triggered was likely to be
> non-zero even if pollwake() is not called before the first
> poll_schedule_timeout(), meaning schedule_hrtimeout_range() would not
> be called and an extra loop calling all ->poll() would be done.
> 
> This patch initialize triggered to 0 in poll_initwait() so the ->poll()
> are not called twice before the process goes to sleep when it needs to.

Indeed, triggered is random stack content, so it needs to be initialized.
 
> Signed-off-by: Guillaume Knispel <gknispel@...formatique.com>

Acked-by: Thomas Gleixner <tglx@...utronix.de>

> ---
>  fs/select.c |    1 +
>  1 files changed, 1 insertions(+), 0 deletions(-)
> 
> diff --git a/fs/select.c b/fs/select.c
> index d870237..8084834 100644
> --- a/fs/select.c
> +++ b/fs/select.c
> @@ -110,6 +110,7 @@ void poll_initwait(struct poll_wqueues *pwq)
>  {
>         init_poll_funcptr(&pwq->pt, __pollwait);
>         pwq->polling_task = current;
> +       pwq->triggered = 0;
>         pwq->error = 0;
>         pwq->table = NULL;
>         pwq->inline_index = 0;
> 
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