Re: [PATCH 40/41] ncpfs: Use set_current_blocked()

Oleg Nesterov
2011-08-17T14:44:39Z

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@intel.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@intel.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
>
>