linux-kernel - Re: [RFC] TIF_NOTIFY_RESUME, arch/*/*/*signal*.c and all such

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Date:	Wed, 2 May 2012 20:30:57 +0200
From:	Oleg Nesterov <oleg@...hat.com>
To:	Al Viro <viro@...IV.linux.org.uk>
Cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	linux-arch@...r.kernel.org, linux-kernel@...r.kernel.org,
	Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [RFC] TIF_NOTIFY_RESUME, arch/*/*/*signal*.c and all such

On 04/29, Al Viro wrote:
>
> 	* Now, if do_notify_resume() does nothing in case !user_mode(regs),
> let's lift that check to (32bit) caller.  What we have right now is
> 	do_notify_resume(%esp, NULL, %ecx)
> 	goto resume_userspace_sig;
> resume_userspace_sig:
> 	if (!user_mode_vm(%esp))
> 		goto resume_kernel;
> resume_userspace:
> So after lifting the check we get
> 	if (user_mode(%esp))
> 		do_notify_resume(%esp, NULL, %ecx)
> 	goto resume_userspace_sig;
> resume_userspace_sig:
> 	if (!user_mode_vm(%esp))
> 		goto resume_kernel;
> resume_userspace:
> but user_mode(regs) being true means that user_mode_vm(regs) is also true,
> so this code is equivalent to
> 	if (!user_mode(%esp))
> 		goto resume_kernel;
> 	do_notify_resume(%esp, NULL, %ecx)
> 	goto resume_userspace;
> (with stuff around resume_userspace_sig left without changes).

Yes, thanks, this looks correct.

I've read the new patches in your tree. Again, I do not have any
useful comment, but a couple of questions.

And just in case... I will be completely offline till May 9.

----------------------------------------
046a099ad7b3791a7f9dfbe56ac1263bda8b1974 arm: if there's no handler we need to restore sigmask, syscall or no syscall

with or without this patch, set_current_blocked(->saved_sigmask) doesn't
look exactly right after force_sigsegv(), this can block SIGSEGV.

And force_sigsegv(sig => 0) looks strange, but this is off-topic.

And the question, I am just curious...

OTOH. I am not sure I understand the "int syscall" argument correctly,
I'll assume it means the same as "regs->orig_ax > 0" on x86. In this
case it is not clear to me how "!syscall && TIF_RESTORE_SIGMASK" is
possible.

x86 does this outside of the "if (syscall_get_nr(current, regs)" block
too. Probably this makes sense because debugger can change orig_ax in
between?

(The same for the next db7fddb9574c175aabdbcaa74b736bb3d1665a8e change
 in unicore32)

----------------------------------------
415a12e79ebfa703a5ec91c85cb29f6ecc844aa1 most of set_current_blocked() callers want SIGKILL/SIGSTOP removed from set

Cosmetic nit. With this patch we have

	void set_current_blocked(sigset_t *newset)
	{
		struct task_struct *tsk = current;
		sigdelsetmask(newset, sigmask(SIGKILL) | sigmask(SIGSTOP));
		spin_lock_irq(&tsk->sighand->siglock);
		__set_task_blocked(tsk, newset);
		spin_unlock_irq(&tsk->sighand->siglock);
	}

but it could simply do

	void set_current_blocked(sigset_t *newset)
	{
		sigdelsetmask(newset, sigmask(SIGKILL) | sigmask(SIGSTOP));
		__set_current_blocked(newset);
	}

-----------------------------------------
fa04e22b239aa035f3ae77151e26b03400303245 FRV: Shrink TIF_WORK_MASK [ver #2]

Off-topic/stupid question. Even if I know nothing about arch/frv, this looks
like a nice change to me because

	#define _TIF_WORK_MASK         0x0000FFFE
	#define _TIF_ALLWORK_MASK      0x0000FFFF

looks very confusing imho. I mean, it is not clear which bits do we actually
want to check.

Can't we (cough, you ;) also cleanup _TIF_WORK_MASK/_TIF_ALLWORK_MASK on x86?

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