Date: Sat, 11 Sep 2021 17:16:23 +0300 From: Andriy Gapon <avg@freebsd.org> To: Mark Johnston <markj@freebsd.org> Cc: "net@FreeBSD.org" <net@freebsd.org>, hackers@freebsd.org Subject: Re: recvmsg() "short receive" after FIONREAD Message-ID: <fcf10f8a-1672-4a21-c64b-55044cac81c5@FreeBSD.org> In-Reply-To: <YTy5kRl0kDl495Po@nuc> References: <500a2272-c1b3-3f97-0096-9fe8117c4b95@FreeBSD.org> <6f455869-cbdd-ee20-f2f8-f633e22071e9@FreeBSD.org> <YTuznrhho4qGXqu8@nuc> <cdd2328e-e6aa-f0fc-a77a-adae03759f18@FreeBSD.org> <4a2165c5-b97b-8fb7-9ada-0acae3197824@FreeBSD.org> <b309f8a5-c550-905b-4340-0b7005ea6fe3@FreeBSD.org> <YTy5kRl0kDl495Po@nuc>
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On 11/09/2021 17:13, Mark Johnston wrote:
> I think the semantic change is ok. Did you change FIONREAD to lock the
> sockbuf? I think it would be necessary to avoid races with pulseaudio:
> sb_acc is modified before sb_ctl, so there could be windows where
> sbavail(sb) - sb->sb_ctl gives a larger.
>
> And, it is not really safe to lock the sockbuf itself, since it may be
> overwritten by a listen(2) call. SOCK_RECVBUF_LOCK(so) should be used
> instead.
I didn't think about the locking, so I didn't add it.
My current patch is trivial:
@@ -210,7 +210,7 @@ soo_ioctl(struct file *fp, u_long cmd, void *data, struct
ucred *active_cred,
if (SOLISTENING(so)) {
error = EINVAL;
} else {
- *(int *)data = sbavail(&so->so_rcv);
+ *(int *)data = sbavail(&so->so_rcv) - so->so_rcv.sb_ctl;
}
break;
Let me try adding the lock.
Thank you again!
--
Andriy Gapon
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