Date: Tue, 13 Nov 2012 15:40:57 -0600 From: Guy Helmer <guy.helmer@gmail.com> To: "freebsd-net@freebsd.org" <freebsd-net@freebsd.org> Subject: bpf hold buffer in-use flag Message-ID: <9C928117-2230-4F01-9B95-B6D945AF4416@gmail.com>
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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
=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);
/*
* If the hold buffer is empty, then do a timed sleep, which
* ends when the timeout expires or when enough packets
@@ -940,27 +944,27 @@ bpfread(struct cdev *dev, struct uio *uio, int iof
/*
* At this point, we know we have something in the hold slot.
*/
+ d->bd_hbuf_in_use =3D 1;
BPFD_UNLOCK(d);
/*
* Move data from hold buffer into user space.
* We know the entire buffer is transferred since
* we checked above that the read buffer is bpf_bufsize bytes.
- *
- * XXXRW: More synchronization needed here: what if a second =
thread
- * issues a read on the same fd at the same time? Don't want =
this
- * getting invalidated.
+ *
+ * We do not have to worry about simultaneous reads because
+ * we waited for sole access to the hold buffer above.
*/
error =3D bpf_uiomove(d, d->bd_hbuf, d->bd_hlen, uio);
BPFD_LOCK(d);
- if (d->bd_hbuf !=3D NULL) {
- /* Free the hold buffer only if it is still valid. */
- d->bd_fbuf =3D d->bd_hbuf;
- d->bd_hbuf =3D NULL;
- d->bd_hlen =3D 0;
- bpf_buf_reclaimed(d);
- }
+ KASSERT(d->bd_hbuf !=3D NULL, ("bpfread: lost bd_hbuf"));
+ d->bd_fbuf =3D d->bd_hbuf;
+ d->bd_hbuf =3D NULL;
+ d->bd_hlen =3D 0;
+ bpf_buf_reclaimed(d);
+ d->bd_hbuf_in_use =3D 0;
+ wakeup(&d->bd_hbuf_in_use);
BPFD_UNLOCK(d);
return (error);
@@ -1114,6 +1118,9 @@ reset_d(struct bpf_d *d)
BPFD_LOCK_ASSERT(d);
+ while (d->bd_hbuf_in_use)
+ mtx_sleep(&d->bd_hbuf_in_use, &d->bd_lock, PRINET,
+ "bd_hbuf", 0);
if ((d->bd_hbuf !=3D NULL) &&
(d->bd_bufmode !=3D BPF_BUFMODE_ZBUF || bpf_canfreebuf(d))) =
{
/* Free the hold buffer. */
@@ -1254,6 +1261,9 @@ bpfioctl(struct cdev *dev, u_long cmd, caddr_t add
BPFD_LOCK(d);
n =3D d->bd_slen;
+ while (d->bd_hbuf_in_use)
+ mtx_sleep(&d->bd_hbuf_in_use, =
&d->bd_lock,
+ PRINET, "bd_hbuf", 0);
if (d->bd_hbuf)
n +=3D d->bd_hlen;
BPFD_UNLOCK(d);
@@ -1967,6 +1977,9 @@ filt_bpfread(struct knote *kn, long hint)
ready =3D bpf_ready(d);
if (ready) {
kn->kn_data =3D d->bd_slen;
+ while (d->bd_hbuf_in_use)
+ mtx_sleep(&d->bd_hbuf_in_use, &d->bd_lock,
+ PRINET, "bd_hbuf", 0);
if (d->bd_hbuf)
kn->kn_data +=3D d->bd_hlen;
} else if (d->bd_rtout > 0 && d->bd_state =3D=3D BPF_IDLE) {
@@ -2299,6 +2312,9 @@ catchpacket(struct bpf_d *d, u_char *pkt, u_int pk
* spot to do it.
*/
if (d->bd_fbuf =3D=3D NULL && bpf_canfreebuf(d)) {
+ while (d->bd_hbuf_in_use)
+ mtx_sleep(&d->bd_hbuf_in_use, &d->bd_lock,
+ PRINET, "bd_hbuf", 0);
d->bd_fbuf =3D d->bd_hbuf;
d->bd_hbuf =3D NULL;
d->bd_hlen =3D 0;
@@ -2341,6 +2357,9 @@ catchpacket(struct bpf_d *d, u_char *pkt, u_int pk
++d->bd_dcount;
return;
}
+ while (d->bd_hbuf_in_use)
+ mtx_sleep(&d->bd_hbuf_in_use, &d->bd_lock,
+ PRINET, "bd_hbuf", 0);
ROTATE_BUFFERS(d);
do_wakeup =3D 1;
curlen =3D 0;
Index: bpf.h
=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.h (revision 242997)
+++ bpf.h (working copy)
@@ -1235,7 +1235,8 @@ SYSCTL_DECL(_net_bpf);
/*
* Rotate the packet buffers in descriptor d. Move the store buffer =
into the
* hold slot, and the free buffer ino the store slot. Zero the length =
of the
- * new store buffer. Descriptor lock should be held.
+ * new store buffer. Descriptor lock should be held. Hold buffer must
+ * not be marked "in use".
*/
#define ROTATE_BUFFERS(d) do { =
\
(d)->bd_hbuf =3D (d)->bd_sbuf; =
\
Index: bpf_buffer.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_buffer.c (revision 242997)
+++ bpf_buffer.c (working copy)
@@ -189,6 +189,9 @@ bpf_buffer_ioctl_sblen(struct bpf_d *d, u_int *i)
return (EINVAL);
}
+ while (d->bd_hbuf_in_use)
+ mtx_sleep(&d->bd_hbuf_in_use, &d->bd_lock,
+ PRINET, "bd_hbuf", 0);
/* Free old buffers if set */
if (d->bd_fbuf !=3D NULL)
free(d->bd_fbuf, M_BPF);
Index: bpfdesc.h
=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
--- bpfdesc.h (revision 242997)
+++ bpfdesc.h (working copy)
@@ -63,6 +63,7 @@ struct bpf_d {
caddr_t bd_sbuf; /* store slot */
caddr_t bd_hbuf; /* hold slot */
caddr_t bd_fbuf; /* free slot */
+ int bd_hbuf_in_use; /* don't rotate buffers */
int bd_slen; /* current length of store =
buffer */
int bd_hlen; /* current length of hold buffer =
*/
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