Re: [PATCH] poll/select: initialize triggered field of struct poll_wqueues

[Andrew Morton <akpm@linux-foundation.org>]

On Sun, 16 Aug 2009 09:53:08 +0900 Tejun Heo <tj@kernel.org> wrote:

> 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.
> > 
> > Signed-off-by: Guillaume Knispel <gknispel@proformatique.com>
> 
> Ah... nice spotting.
> 
> Acked-by: Tejun Heo <tj@kernel.org>
> 

OK, thanks.

I tagged this for -stable backporting.  That isn't strictly needed, as
there's no particular harm caused here.  But using an uninitialised
variable in the core poll/select code is pretty gross.