linux-kernel - Re: [patch 2/9] signalfd/timerfd

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Message-ID: <Pine.LNX.4.64.0703111108460.12947@alien.or.mcafeemobile.com>
Date:	Sun, 11 Mar 2007 11:14:42 -0700 (PDT)
From:	Davide Libenzi <davidel@...ilserver.org>
To:	Oleg Nesterov <oleg@...sign.ru>
cc:	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>
Subject: Re: [patch 2/9] signalfd/timerfd - signalfd core ...

On Sun, 11 Mar 2007, Oleg Nesterov wrote:

> On 03/10, Davide Libenzi wrote:
> >
> > +static void signalfd_put_sighand(struct signalfd_ctx *ctx,
> > +				 struct sighand_struct *sighand,
> > +				 unsigned long *flags)
> > +{
> > +	unlock_task_sighand(ctx->tsk, flags);
> > +}
> 
> Note that signalfd_put_sighand() doesn't need "sighand" parameter, please
> see below.

I want it to return the sighand, and for simmetry I prefer the "put" to be 
passed the parameter back too. Even if not used.



> > +int signalfd_deliver(struct sighand_struct *sighand, int sig,
> > +		     struct siginfo *info)
> > +{
> > +	int nsig = 0;
> > +	struct signalfd_ctx *ctx, *tmp;
> > +
> > +	list_for_each_entry_safe(ctx, tmp, &sighand->sfdlist, lnk) {
> > +		/*
> > +		 * We use a negative signal value as a way to broadcast that the
> > +		 * sighand has been orphaned, so that we can notify all the
> > +		 * listeners about this. Remeber the ctx->sigmask is inverted,
> > +		 * so if the user is interested in a signal, that corresponding
> > +		 * bit will be zero.
> > +		 */
> > +		if (sig < 0)
> > +			list_del_init(&ctx->lnk);
> 
> I'm afraid this is not right. This should be per-thread.
> 
> Suppose we have threads T1 and T2 from the same thread group. sighand->sfdlist
> contains ctx1 and ctx2 "linked" to T1 and T2. Now, T1 exits, __exit_signal()
> does signalfd_notify(sighand, -1), and "unlinks" all threads, not just T1.
> 
> IOW, we should do
> 
> 	if (ctx->tsk == current) {
> 		list_del_init(&ctx->lnk);
> 		wake_up(&ctx->wqh);
> 	}

Yes, of course. Dunno why the change got lost.



> Perhaps it makes sense to not re-use signalfd_deliver(), but introduce
> a new signalfd_xxx(sighand, tsk) helper for de_thread/exit_signal.
> 
> Btw, signalfd_deliver() doesn't use "info" parameter.
> 
> > +		if (sig < 0 || !sigismember(&ctx->sigmask, sig)) {
> > +			wake_up(&ctx->wqh);
> 
> Minor nit. Perhaps it makes sense to do
> 
> 	void signalfd_deliver(struct task_struct *tsk, int sig, struct sigpending *pending)
> 	{
> 		struct sighand_struct *sighand = tsk->sighand;
> 		int private = (tsk->pending == pending);
> 
> 		list_for_each_entry_safe(ctx, tmp, &sighand->sfdlist, lnk) {
> 			if (private && ctx->tsk != tsk)
> 				continue;
> 			if (!sigismember(&ctx->sigmask, sig))
> 				wake_up(&ctx->wqh);
> 		}
> 	}
> 
> Even better: signalfd_deliver(struct task_struct *tsk, int sig, int private).
> This way specific_send_sig_info/send_sigqueue won't do a "false" wakeup.

I agree in the latter.



> > +asmlinkage long sys_signalfd(int ufd, sigset_t __user *user_mask, size_t sizemask)
> > +{
> > ...
> > +		if ((sighand = signalfd_get_sighand(ctx, &flags)) != NULL) {
> > +			ctx->sigmask = sigmask;
> > +			signalfd_put_sighand(ctx, sighand, &flags);
> > +		}
> 
> This looks like unneeded complication to me, I'd suggest
> 
> 		if (signalfd_get_sighand(ctx, &flags)) {
> 			ctx->sigmask = sigmask;
> 			signalfd_put_sighand(ctx, flags);
> 		}
> 
> unlock_task_sighand() (and thus signalfd_put_sighand) doesn't need "sighand"
> parameter. signalfd_get_sighand() is in fact boolean. It makes sense to return
> sighand, it may be useful, but this patch only needs != NULL.
> 
> Every usage of signalfd_get_sighand() could be simplified accordingly.

As I said before, I prefer that way.


> > +	 * Tell all the sighand listeners that this sighand has
> > +	 * been detached. Needs to be called with the sighand lock
> > +	 * held.
> > +	 */
> > +	if (unlikely(!list_empty(&oldsighand->sfdlist))) {
> > +		spin_lock_irq(&oldsighand->siglock);
> > +		signalfd_notify(oldsighand, -1, NULL);
> > +		spin_unlock_irq(&oldsighand->siglock);
> > +	}
> 
> Very minor nit. I'd suggest to make a new helper and put it in signalfd.h
> (like signalfd_notify()). This will help CONFIG_SIGNALFD.

Yes, makes sense.



- Davide


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