Date: Thu, 23 May 2013 16:05:39 -0500 From: Guy Helmer <guy.helmer@gmail.com> To: John Baldwin <jhb@freebsd.org> Cc: freebsd-net@freebsd.org Subject: Re: bpf hold buffer in-use flag Message-ID: <4EA47178-7CE2-40CE-A767-2689FAF7BEBD@gmail.com> In-Reply-To: <201301091535.04904.jhb@freebsd.org> References: <9C928117-2230-4F01-9B95-B6D945AF4416@gmail.com> <201301091535.04904.jhb@freebsd.org>
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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=20
> these changes to add a flag to indicate when the hold buffer cannot be=20=
> modified because it is in use. Since it's my first time using =
mtx_sleep() and=20
> wakeup(), I wanted to run these past the list to see if I can get any =
feedback=20
> on the approach.
>>=20
>>=20
>> Index: bpf.c
>> =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=
=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=
=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D
>> --- 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 =3D 0;
>> d->bd_bufmode =3D BPF_BUFMODE_BUFFER;
>> d->bd_sig =3D SIGIO;
>> d->bd_direction =3D BPF_D_INOUT;
>> @@ -872,6 +873,9 @@ bpfread(struct cdev *dev, struct uio *uio, int =
iof
>> callout_stop(&d->bd_callout);
>> timed_out =3D (d->bd_state =3D=3D BPF_TIMED_OUT);
>> d->bd_state =3D BPF_IDLE;
>> + while (d->bd_hbuf_in_use)
>> + mtx_sleep(&d->bd_hbuf_in_use, &d->bd_lock,
>> + PRINET|PCATCH, "bd_hbuf", 0);
>=20
> You need to check the return value here, otherwise the PCATCH is =
useless (you=20
> will just go back to sleep instead of failing with an error if this is=20=
> interrupted by a signal).=20
Thanks for the feedback (sorry it's taken so long to get to it). Would =
this change correctly handle interruptions?
Index: bpf.c
=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=
=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=
=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D
--- bpf.c (revision 250941)
+++ bpf.c (working copy)
@@ -856,9 +856,14 @@
callout_stop(&d->bd_callout);
timed_out =3D (d->bd_state =3D=3D BPF_TIMED_OUT);
d->bd_state =3D 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 =3D mtx_sleep(&d->bd_hbuf_in_use, &d->bd_lock,
PRINET|PCATCH, "bd_hbuf", 0);
+ if (error =3D=3D EINTR || error =3D=3D ERESTART) {
+ BPFD_UNLOCK(d);
+ return (error);
+ }
+ }
/*
* If the hold buffer is empty, then do a timed sleep, which
* ends when the timeout expires or when enough packets
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