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

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Date:	Wed, 17 Aug 2011 16:41:39 +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>, linux-fsdevel@...r.kernel.org,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH 40/41] ncpfs: Use set_current_blocked()

On 08/17, Matt Fleming wrote:
>
> On Wed, 2011-08-17 at 14:04 +0200, Oleg Nesterov wrote:
> > On 08/16, Matt Fleming wrote:
> > >
> > > > the sighand->action[] checks are racy anyway in the mt case, siglock
> > > > can't help.
> > >
> > > Hmm.. really? I thought that ->siglock serialised modifications to
> > > sighand->action[] even in the mt case, no?
> >
> > Sure. But another thread can change sighand->action[] right after we
> > drop ->siglock. So how can this lock help? We simply read the word,
> > this is atomic and doesn't need the locking.
>
> Oh right, in the scenario in ncp_do_request(), sure I understand that. I
> thought you were saying that in the general case ->siglock doesn't
> protect sighand->action[]! That's why I was confused ;-)
>
> OK, how about this patch (instead of 40/41) which gets rid of all the
> nasties? I've Cc'd linux-fsdevel so people can hopefully OK this from a
> file system perspective.

Well, of course I am in no position to ack this change ;)

But obviously I like the idea to kill the obviously wrong code.
In particular, the PF_EXITING/SIGKILL logic looks as "must die
in any case" to me.

If maintainers object, you can remove ->siglock and convert the code
to use set_current_blocked(). IOW, simplify your original patch.

Oleg.

> From bb1650295054bdfa96f8f4ff61507d314be8296a Mon Sep 17 00:00:00 2001
> From: Matt Fleming <matt.fleming@...el.com>
> Date: Wed, 17 Aug 2011 13:59:12 +0100
> Subject: [PATCH] ncpfs: Don't attempt to mask signals during
>  do_ncp_rpc_call()
> 
> Delete the code in ncp_do_request() that attempts to mask signals
> across the call to do_ncp_rpc_call(). This code was racy because it
> dropped ->siglock across do_ncp_rpc_call() so it was possible for
> another thread to modify the signal handlers, which made the code
> pointless.
> 
> Instead of fixing the code to hold the lock across the call let's just
> delete it because, as the FIXME comment (which has been around since
> the beginning of git history) says, trying to block signals doesn't
> seem right at all.
> 
> Signed-off-by: Matt Fleming <matt.fleming@...el.com>
> ---
>  fs/ncpfs/sock.c |   32 +-------------------------------
>  1 files changed, 1 insertions(+), 31 deletions(-)
> 
> diff --git a/fs/ncpfs/sock.c b/fs/ncpfs/sock.c
> index 3a15872..6618402 100644
> --- a/fs/ncpfs/sock.c
> +++ b/fs/ncpfs/sock.c
> @@ -748,38 +748,8 @@ static int ncp_do_request(struct ncp_server *server, int size,
>  	if (!ncp_conn_valid(server)) {
>  		return -EIO;
>  	}
> -	{
> -		sigset_t old_set;
> -		unsigned long mask, flags;
> -
> -		spin_lock_irqsave(&current->sighand->siglock, flags);
> -		old_set = current->blocked;
> -		if (current->flags & PF_EXITING)
> -			mask = 0;
> -		else
> -			mask = sigmask(SIGKILL);
> -		if (server->m.flags & NCP_MOUNT_INTR) {
> -			/* FIXME: This doesn't seem right at all.  So, like,
> -			   we can't handle SIGINT and get whatever to stop?
> -			   What if we've blocked it ourselves?  What about
> -			   alarms?  Why, in fact, are we mucking with the
> -			   sigmask at all? -- r~ */
> -			if (current->sighand->action[SIGINT - 1].sa.sa_handler == SIG_DFL)
> -				mask |= sigmask(SIGINT);
> -			if (current->sighand->action[SIGQUIT - 1].sa.sa_handler == SIG_DFL)
> -				mask |= sigmask(SIGQUIT);
> -		}
> -		siginitsetinv(&current->blocked, mask);
> -		recalc_sigpending();
> -		spin_unlock_irqrestore(&current->sighand->siglock, flags);
> -		
> -		result = do_ncp_rpc_call(server, size, reply, max_reply_size);
>  
> -		spin_lock_irqsave(&current->sighand->siglock, flags);
> -		current->blocked = old_set;
> -		recalc_sigpending();
> -		spin_unlock_irqrestore(&current->sighand->siglock, flags);
> -	}
> +	result = do_ncp_rpc_call(server, size, reply, max_reply_size);
>  
>  	DDPRINTK("do_ncp_rpc_call returned %d\n", result);
>  
> -- 
> 1.7.4.4
> 
> 

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