linux-kernel - msleep(1000) vs. schedule_timeout

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Message-ID: <20070617161439.8470.qmail@science.horizon.com>
Date:	17 Jun 2007 12:14:39 -0400
From:	linux@...izon.com
To:	linux-kernel@...r.kernel.org
Cc:	linux@...izon.com
Subject: msleep(1000) vs. schedule_timeout_uninterruptible(HZ+1)

I was looking at some of the stupider code that calls msleep(),
particularly that which does
	msleep(jiffies_to_msecs(jiff))

and I noticed that msleep() just calls schedule_timeout_uninterruptible().
But it does it in a loop.

The basic question is, when does the loop make a difference?
Is it only when you're on a wait queue?  Or are there other kinds of
unexpected wakeups that can arrive?

I see all kinds of uses of both kinds for simple "wait a while" operations,
and I'm not sure if one is more correct than the other.

(And, in drivers/media/video/cpia2/cpia2_v4l.c:cpia2_exit(), a lovely
example of calling schedule_timeout() without set_current_state() first.)
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