git: 61a14ddfe012 - main - unix: Fix a lock order reveral

The branch main has been updated by markj:

URL: https://cgit.FreeBSD.org/src/commit/?id=61a14ddfe012ca7b57a101725e5c654269f200ca

commit 61a14ddfe012ca7b57a101725e5c654269f200ca
Author:     Mark Johnston <markj@FreeBSD.org>
AuthorDate: 2023-09-27 12:24:11 +0000
Commit:     Mark Johnston <markj@FreeBSD.org>
CommitDate: 2023-09-27 12:29:34 +0000

    unix: Fix a lock order reveral
    
    Running the test suite yields:
    
    lock order reversal:
     1st 0xfffff80004bc6700 unp (unp, sleep mutex) @ sys/kern/uipc_usrreq.c:390
     2nd 0xffffffff81a94b30 unp_link_rwlock (unp_link_rwlock, rw) @ sys/kern/uipc_usrreq.c:2934
    lock order unp -> unp_link_rwlock attempted at:
    0xffffffff80bc216e at witness_checkorder+0xbbe
    0xffffffff80b493a5 at _rw_wlock_cookie+0x65
    0xffffffff80c0a8e2 at unp_discard+0x22
    0xffffffff80c0a888 at unp_freerights+0x38
    0xffffffff80c09fdd at unp_scan+0x9d
    0xffffffff80c0f9a7 at uipc_sosend_dgram+0x727
    0xffffffff80c00a79 at sousrsend+0x79
    0xffffffff80c072d0 at kern_sendit+0x1c0
    0xffffffff80c074d7 at sendit+0xb7
    0xffffffff80c076f3 at sys_sendmsg+0x63
    0xffffffff8104d957 at amd64_syscall+0x6b7
    0xffffffff8101f9eb at fast_syscall_common+0xf8
    
    This happens when uipc_sosend_dgram() discards a control message because
    the receive socket buffer is full.  The overflow handling frees
    internalized file references in the socket buffer before freeing mbufs.
    It does this with socket PCBs locked, leading to the LOR.  Defer
    handling of file references until the PCBs are unlocked.
    
    Reviewed by:    glebius
    MFC after:      1 week
    Differential Revision:  https://reviews.freebsd.org/D41884
---
 sys/kern/uipc_usrreq.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/sys/kern/uipc_usrreq.c b/sys/kern/uipc_usrreq.c
index 291ff7cf8cae..f12693f3982a 100644
--- a/sys/kern/uipc_usrreq.c
+++ b/sys/kern/uipc_usrreq.c
@@ -1332,8 +1332,10 @@ uipc_sosend_dgram(struct socket *so, struct sockaddr *addr, struct uio *uio,
 	} else {
 		soroverflow_locked(so2);
 		error = ENOBUFS;
-		if (f->m_next->m_type == MT_CONTROL)
-			unp_scan(f->m_next, unp_freerights);
+		if (f->m_next->m_type == MT_CONTROL) {
+			c = f->m_next;
+			f->m_next = NULL;
+		}
 	}
 
 	if (addr != NULL)