ifnet: vnet_if_return(): Avoid unnecessary recursive acquisition of ifnet_detach_sxlock

vnet_if_return() will be invocked by vnet_sysuninit() on vnet destructing,
while the lock ifnet_detach_sxlock has been acquired in vnet_destroy()
already.

With this change the order of locking is more clear. There should be no
functional change.

Reviewed by:	pouria
Fixes:		868bf82153e8 if: avoid interface destroy race
MFC after:	1 week
Differential Revision:	https://reviews.freebsd.org/D56288

1 files changed, 2 insertions, 2 deletions

diff --git a/sys/net/if.c b/sys/net/if.c
index 519b23750b52..73138716cf46 100644
--- a/sys/net/if.c
+++ b/sys/net/if.c
@@ -479,6 +479,8 @@ vnet_if_return(const void *unused __unused)
 
 	i = 0;
 
+	/* The lock has already been aquired in vnet_destroy() */
+	sx_assert(&ifnet_detach_sxlock, SX_XLOCKED);
 	/*
 	 * We need to protect our access to the V_ifnet tailq. Ordinarily we'd
 	 * enter NET_EPOCH, but that's not possible, because if_vmove() calls
@@ -507,9 +509,7 @@ vnet_if_return(const void *unused __unused)
 	IFNET_WUNLOCK();
 
 	for (int j = 0; j < i; j++) {
-		sx_xlock(&ifnet_detach_sxlock);
 		if_vmove(pending[j], pending[j]->if_home_vnet);
-		sx_xunlock(&ifnet_detach_sxlock);
 	}
 
 	free(pending, M_IFNET);