Date: Sat, 11 Sep 2021 21:25:42 +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: <82143b59-a0e6-c23e-8b47-29d8d41eb5b4@FreeBSD.org> In-Reply-To: <4499e2b0-d1e7-5bee-519c-783fb930fc06@FreeBSD.org> 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> <fcf10f8a-1672-4a21-c64b-55044cac81c5@FreeBSD.org> <4499e2b0-d1e7-5bee-519c-783fb930fc06@FreeBSD.org>
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On 11/09/2021 17:28, Andriy Gapon wrote:
> On 11/09/2021 17:16, Andriy Gapon wrote:
>> 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.
>
> By the way, soo_stat() seems to be another good example to follow.
So, this is what I've got:
diff --git a/sys/kern/sys_socket.c b/sys/kern/sys_socket.c
index e53b0367960b..11ee03703407 100644
--- a/sys/kern/sys_socket.c
+++ b/sys/kern/sys_socket.c
@@ -210,7 +210,12 @@ 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);
+ struct sockbuf *sb;
+
+ sb = &so->so_rcv;
+ SOCKBUF_LOCK(sb);
+ *(int *)data = sbavail(sb) - sb->sb_ctl;
+ SOCKBUF_UNLOCK(sb);
}
break;
--
Andriy Gapon
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