Instead of spamming the console on each curvnet recursion event, print

out each such call graph only once, along with a stack backtrace.  This
should make kernels built with VNET_DEBUG reasonably usable again in
busy / production environments.

Introduce a new DDB command "show vnetrcrs" which dumps the whole log
of distinctive curvnet recursion events.  This might be useful when
recursion reports get burried / lost too deep in the message buffer.
In the later case stack backtraces are not available.

Reviewed by:	bz
MFC after:	3 days

1 files changed, 71 insertions, 0 deletions

diff --git a/sys/net/vnet.c b/sys/net/vnet.c
index 298ffb2..26635db 100644
--- a/sys/net/vnet.c
+++ b/sys/net/vnet.c
@@ -37,8 +37,10 @@
 __FBSDID("$FreeBSD$");
 
 #include "opt_ddb.h"
+#include "opt_kdb.h"
 
 #include <sys/param.h>
+#include <sys/kdb.h>
 #include <sys/kernel.h>
 #include <sys/jail.h>
 #include <sys/systm.h>
@@ -616,6 +618,65 @@ vnet_sysuninit(void)
 	VNET_SYSINIT_RUNLOCK();
 }
 
+#ifdef VNET_DEBUG
+struct vnet_recursion {
+	SLIST_ENTRY(vnet_recursion)	 vnr_le;
+	const char			*prev_fn;
+	const char			*where_fn;
+	int				 where_line;
+	struct vnet			*old_vnet;
+	struct vnet			*new_vnet;
+};
+
+static SLIST_HEAD(, vnet_recursion) vnet_recursions =
+    SLIST_HEAD_INITIALIZER(vnet_recursions);
+
+static void
+vnet_print_recursion(struct vnet_recursion *vnr, int brief)
+{
+
+	if (!brief)
+		printf("CURVNET_SET() recursion in ");
+	printf("%s() line %d, prev in %s()", vnr->where_fn, vnr->where_line,
+	    vnr->prev_fn);
+	if (brief)
+		printf(", ");
+	else
+		printf("\n    ");
+	printf("%p -> %p\n", vnr->old_vnet, vnr->new_vnet);
+}
+
+void
+vnet_log_recursion(struct vnet *old_vnet, const char *old_fn, int line)
+{
+	struct vnet_recursion *vnr;
+
+	/* Skip already logged recursion events. */
+	SLIST_FOREACH(vnr, &vnet_recursions, vnr_le)
+		if (vnr->prev_fn == old_fn &&
+		    vnr->where_fn == curthread->td_vnet_lpush &&
+		    vnr->where_line == line &&
+		    (vnr->old_vnet == vnr->new_vnet) == (curvnet == old_vnet))
+			return;
+
+	vnr = malloc(sizeof(*vnr), M_VNET, M_NOWAIT | M_ZERO);
+	if (vnr == NULL)
+		panic("%s: malloc failed", __func__);
+	vnr->prev_fn = old_fn;
+	vnr->where_fn = curthread->td_vnet_lpush;
+	vnr->where_line = line;
+	vnr->old_vnet = old_vnet;
+	vnr->new_vnet = curvnet;
+
+	SLIST_INSERT_HEAD(&vnet_recursions, vnr, vnr_le);
+
+	vnet_print_recursion(vnr, 0);
+#ifdef KDB
+	kdb_backtrace();
+#endif
+}
+#endif /* VNET_DEBUG */
+
 #ifdef DDB
 DB_SHOW_COMMAND(vnets, db_show_vnets)
 {
@@ -637,4 +698,14 @@ DB_SHOW_COMMAND(vnets, db_show_vnets)
 			break;
 	}
 }
+
+#ifdef VNET_DEBUG
+DB_SHOW_COMMAND(vnetrcrs, db_show_vnetrcrs)
+{
+	struct vnet_recursion *vnr;
+
+	SLIST_FOREACH(vnr, &vnet_recursions, vnr_le)
+		vnet_print_recursion(vnr, 1);
+}
 #endif
+#endif /* DDB */