bpf hold buffer in-use flag

[Guy Helmer]

On Jan 9, 2013, at 2:35 PM, John Baldwin <jhb at 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?

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);
+		}
+	}
 	/*
 	 * If the hold buffer is empty, then do a timed sleep, which
 	 * ends when the timeout expires or when enough packets