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

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Date:	Sat, 15 Aug 2009 19:30:24 +0200
From:	Guillaume Knispel <gknispel@...formatique.com>
To:	linux-kernel@...r.kernel.org
Cc:	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>,
	Thomas Gleixner <tglx@...utronix.de>,
	linux-fsdevel@...r.kernel.org
Subject: [PATCH] poll/select: initialize triggered field of struct
 poll_wqueues

Hi,

That's only the second time I read fs/select.c so this has to be
reviewed carefully.
It has been quickly tested on my Debian Lenny x86_32 box and everything
seems to works fine on the surface.

Cheers,
Guillaume Knispel

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.

Signed-off-by: Guillaume Knispel <gknispel@...formatique.com>
---
 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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