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

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

[Guillaume Knispel]

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@proformatique.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;

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

[Thomas Gleixner]

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@proformatique.com>

Acked-by: Thomas Gleixner <tglx@linutronix.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;
> 

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

[Tejun Heo]

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>

Thanks.

-- 
tejun

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

[Andrew Morton]

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.

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

[Tejun Heo]

Hello,

Andrew Morton wrote:
> 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.

Yes, I was thinking about putting this for -stable too.  It's not
critical but still.

Thanks.

-- 
tejun

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

[Linus Torvalds]

On Sat, 15 Aug 2009, Andrew Morton wrote:
> 
> 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.

Hmm. I committed it when Tejun's ack came in, but I didn't tag it for 
stable. Oh well.

		Linus

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

[Linus Torvalds]

On Sat, 15 Aug 2009, Linus Torvalds wrote:
> 
> Hmm. I committed it when Tejun's ack came in, but I didn't tag it for 
> stable. Oh well.

Oh, actually, I noticed that I hadn't pushed it out yet. So I added the 
stable tag and did so.

		Linus