Date: Thu, 23 May 2013 17:28:05 -0400 From: John Baldwin <jhb@freebsd.org> To: Guy Helmer <guy.helmer@gmail.com> Cc: freebsd-net@freebsd.org Subject: Re: bpf hold buffer in-use flag Message-ID: <201305231728.05253.jhb@freebsd.org> In-Reply-To: <4EA47178-7CE2-40CE-A767-2689FAF7BEBD@gmail.com> References: <9C928117-2230-4F01-9B95-B6D945AF4416@gmail.com> <201301091535.04904.jhb@freebsd.org> <4EA47178-7CE2-40CE-A767-2689FAF7BEBD@gmail.com>
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On Thursday, May 23, 2013 5:05:39 pm Guy Helmer wrote: > > On Jan 9, 2013, at 2:35 PM, John Baldwin <jhb@freebsd.org> wrote: > > > On Tuesday, November 13, 2012 4:40:57 pm Guy Helmer wrote: > >> To try to completely resolve the race in bpfread(), I have put together > > these changes to add a flag to indicate when the hold buffer cannot be > > modified because it is in use. Since it's my first time using mtx_sleep() and > > wakeup(), I wanted to run these past the list to see if I can get any feedback > > on the approach. > >> > >> > >> Index: bpf.c > >> =================================================================== > >> --- bpf.c (revision 242997) > >> +++ bpf.c (working copy) > >> @@ -819,6 +819,7 @@ bpfopen(struct cdev *dev, int flags, int fmt, stru > >> * particular buffer method. > >> */ > >> bpf_buffer_init(d); > >> + d->bd_hbuf_in_use = 0; > >> d->bd_bufmode = BPF_BUFMODE_BUFFER; > >> d->bd_sig = SIGIO; > >> d->bd_direction = BPF_D_INOUT; > >> @@ -872,6 +873,9 @@ bpfread(struct cdev *dev, struct uio *uio, int iof > >> callout_stop(&d->bd_callout); > >> timed_out = (d->bd_state == BPF_TIMED_OUT); > >> d->bd_state = BPF_IDLE; > >> + while (d->bd_hbuf_in_use) > >> + mtx_sleep(&d->bd_hbuf_in_use, &d->bd_lock, > >> + PRINET|PCATCH, "bd_hbuf", 0); > > > > You need to check the return value here, otherwise the PCATCH is useless (you > > will just go back to sleep instead of failing with an error if this is > > interrupted by a signal). > > Thanks for the feedback (sorry it's taken so long to get to it). Would this > change correctly handle interruptions? Yes. > Index: bpf.c > =================================================================== > --- bpf.c (revision 250941) > +++ bpf.c (working copy) > @@ -856,9 +856,14 @@ > callout_stop(&d->bd_callout); > timed_out = (d->bd_state == BPF_TIMED_OUT); > d->bd_state = BPF_IDLE; > - while (d->bd_hbuf_in_use) > - mtx_sleep(&d->bd_hbuf_in_use, &d->bd_lock, > + while (d->bd_hbuf_in_use) { > + error = mtx_sleep(&d->bd_hbuf_in_use, &d->bd_lock, > PRINET|PCATCH, "bd_hbuf", 0); > + if (error == EINTR || error == ERESTART) { > + BPFD_UNLOCK(d); > + return (error); > + } > + } Maybe simplify the check to just 'if (error != 0)'? -- John Baldwin
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