linux-kernel - Re: [PATCH 40/41] ncpfs: Use set_current

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Message-ID: <20110816175643.GI29190@redhat.com>
Date:	Tue, 16 Aug 2011 19:56:43 +0200
From:	Oleg Nesterov <oleg@...hat.com>
To:	Matt Fleming <matt@...sole-pimps.org>
Cc:	linux-kernel@...r.kernel.org, Petr Vandrovec <petr@...drovec.name>,
	Al Viro <viro@...iv.linux.org.uk>,
	Arnd Bergmann <arnd@...db.de>
Subject: Re: [PATCH 40/41] ncpfs: Use set_current_blocked()

On 08/11, Matt Fleming wrote:
>
> As described in e6fa16ab ("signal: sigprocmask() should do
> retarget_shared_pending()") the modification of current->blocked is
> incorrect as we need to check whether the signal we're about to block
> is pending in the shared queue.

I'd wish I could understand this code but this seems impossible ;)
IOW, "This doesn't seem right at all." looks reasonable, and the
PF_EXITING adds even more confusion.

As for this patch, it looks (almost) fine anyway. But,

> @@ -749,7 +749,7 @@ static int ncp_do_request(struct ncp_server *server, int size,
>  		return -EIO;
>  	}
>  	{
> -		sigset_t old_set;
> +		sigset_t old_set, blocked;
>  		unsigned long mask, flags;
>  
>  		spin_lock_irqsave(&current->sighand->siglock, flags);
> @@ -769,16 +769,14 @@ static int ncp_do_request(struct ncp_server *server, int size,
>  			if (current->sighand->action[SIGQUIT - 1].sa.sa_handler == SIG_DFL)
>  				mask |= sigmask(SIGQUIT);
>  		}
> -		siginitsetinv(&current->blocked, mask);
> -		recalc_sigpending();
> +
> +		siginitsetinv(&blocked, mask);
> +		__set_task_blocked(current, &blocked);
>  		spin_unlock_irqrestore(&current->sighand->siglock, flags);

Why do we take ->siglock in the first place?

I think it is not needed. We can calculate mask/blocked lockless and
use set_task_blocked(). This also makes sense because __set_task_blocked
is not exported ;)

the sighand->action[] checks are racy anyway in the mt case, siglock
can't help.

Oleg.

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