On Tue, Nov 13, 2012 at 05:49:51PM +0100, Oleg Nesterov wrote:
> On 11/13, Cyrill Gorcunov wrote:
> >
> > struct signalfd_ctx {
> > + rwlock_t lock;
> > sigset_t sigmask;
>
> Oh, I don't think.
>
> rwlock_t is horrible in general, and what it can buy for signalfd?
> A plain spinlock would be better. Or seqlock_t.
>
> Whatever you do, you are trying to introduce the lock which should
> serialize the access to ->sigmask correctly. In this case I think
> you should split this change into 2 patches. The first one should
> fix the locking, imo. sys_signalfd4() should not use ->siglock at
> all, and the users which take ->siglock to read ->sigmask should be
> updated.
I see
>
> Or,
>
> > +#ifdef CONFIG_PROC_FS
> > +static int signalfd_show_fdinfo(struct seq_file *m, struct file *f)
> > +{
> > + struct signalfd_ctx *ctx = f->private_data;
> > + sigset_t sigmask;
> > +
> > + read_lock(&ctx->lock);
> > + sigmask = ctx->sigmask;
> > + read_unlock(&ctx->lock);
>
> Just read ctx->sigmask lockless. Do we really care if show_fdinfo()
> reads the value "in between" ?
As from c/r patch I think we can read it lockless (since we do stop
tasks anyway before doing checkpoint). So I would prefer to provide
it without locks at all.
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