diff --git a/sys/conf/options b/sys/conf/options
index 6957a2d236ef..875a3bc461e0 100644
--- a/sys/conf/options
+++ b/sys/conf/options
@@ -712,6 +712,8 @@ WITNESS_SKIPSPIN	opt_witness.h
 WITNESS_COUNT		opt_witness.h
 OPENSOLARIS_WITNESS	opt_global.h
 
+EPOCH_TRACE		opt_epoch.h
+
 # options for ACPI support
 ACPI_DEBUG		opt_acpi.h
 ACPI_MAX_TASKS		opt_acpi.h
diff --git a/sys/kern/kern_thread.c b/sys/kern/kern_thread.c
index 378bdb88d3a6..cf5beb4acfbc 100644
--- a/sys/kern/kern_thread.c
+++ b/sys/kern/kern_thread.c
@@ -668,6 +668,7 @@ thread_link(struct thread *td, struct proc *p)
 	LIST_INIT(&td->td_contested);
 	LIST_INIT(&td->td_lprof[0]);
 	LIST_INIT(&td->td_lprof[1]);
+	SLIST_INIT(&td->td_epochs);
 	sigqueue_init(&td->td_sigqueue, p);
 	callout_init(&td->td_slpcallout, 1);
 	TAILQ_INSERT_TAIL(&p->p_threads, td, td_plist);
@@ -684,6 +685,8 @@ thread_unlink(struct thread *td)
 	struct proc *p = td->td_proc;
 
 	PROC_LOCK_ASSERT(p, MA_OWNED);
+	MPASS(SLIST_EMPTY(&td->td_epochs));
+
 	TAILQ_REMOVE(&p->p_threads, td, td_plist);
 	p->p_numthreads--;
 	/* could clear a few other things here */
diff --git a/sys/kern/subr_epoch.c b/sys/kern/subr_epoch.c
index aec3a70c27d2..c76697b91608 100644
--- a/sys/kern/subr_epoch.c
+++ b/sys/kern/subr_epoch.c
@@ -30,7 +30,6 @@
 __FBSDID("$FreeBSD$");
 
 #include <sys/param.h>
-#include <sys/types.h>
 #include <sys/systm.h>
 #include <sys/counter.h>
 #include <sys/epoch.h>
@@ -47,6 +46,11 @@ __FBSDID("$FreeBSD$");
 #include <sys/smp.h>
 #include <sys/sysctl.h>
 #include <sys/turnstile.h>
+#ifdef EPOCH_TRACE
+#include <machine/stdarg.h>
+#include <sys/stack.h>
+#include <sys/tree.h>
+#endif
 #include <vm/vm.h>
 #include <vm/vm_extern.h>
 #include <vm/vm_kern.h>
@@ -80,6 +84,7 @@ struct epoch {
 	struct sx e_drain_sx;
 	struct mtx e_drain_mtx;
 	volatile int e_drain_count;
+	const char *e_name;
 };
 
 /* arbitrary --- needs benchmarking */
@@ -134,6 +139,103 @@ __read_mostly epoch_t global_epoch_preempt;
 static void epoch_call_task(void *context __unused);
 static 	uma_zone_t pcpu_zone_record;
 
+#ifdef EPOCH_TRACE
+struct stackentry {
+	RB_ENTRY(stackentry) se_node;
+	struct stack se_stack;
+};
+
+static int
+stackentry_compare(struct stackentry *a, struct stackentry *b)
+{
+
+	if (a->se_stack.depth > b->se_stack.depth)
+		return (1);
+	if (a->se_stack.depth < b->se_stack.depth)
+		return (-1);
+	for (int i = 0; i < a->se_stack.depth; i++) {
+		if (a->se_stack.pcs[i] > b->se_stack.pcs[i])
+			return (1);
+		if (a->se_stack.pcs[i] < b->se_stack.pcs[i])
+			return (-1);
+	}
+
+	return (0);
+}
+
+RB_HEAD(stacktree, stackentry) epoch_stacks = RB_INITIALIZER(&epoch_stacks);
+RB_GENERATE_STATIC(stacktree, stackentry, se_node, stackentry_compare);
+
+static struct mtx epoch_stacks_lock;
+MTX_SYSINIT(epochstacks, &epoch_stacks_lock, "epoch_stacks", MTX_DEF);
+
+static void epoch_trace_report(const char *fmt, ...) __printflike(1, 2);
+static inline void
+epoch_trace_report(const char *fmt, ...)
+{
+	va_list ap;
+	struct stackentry se, *new;
+
+	stack_zero(&se.se_stack);	/* XXX: is it really needed? */
+	stack_save(&se.se_stack);
+
+	/* Tree is never reduced - go lockless. */
+	if (RB_FIND(stacktree, &epoch_stacks, &se) != NULL)
+		return;
+
+	new = malloc(sizeof(*new), M_STACK, M_NOWAIT);
+	if (new != NULL) {
+		bcopy(&se.se_stack, &new->se_stack, sizeof(struct stack));
+
+		mtx_lock(&epoch_stacks_lock);
+		new = RB_INSERT(stacktree, &epoch_stacks, new);
+		mtx_unlock(&epoch_stacks_lock);
+		if (new != NULL)
+			free(new, M_STACK);
+	}
+
+	va_start(ap, fmt);
+	(void)vprintf(fmt, ap);
+	va_end(ap);
+	stack_print_ddb(&se.se_stack);
+}
+
+static inline void
+epoch_trace_enter(struct thread *td, epoch_t epoch, epoch_tracker_t et,
+    const char *file, int line)
+{
+	epoch_tracker_t iet;
+
+	SLIST_FOREACH(iet, &td->td_epochs, et_tlink)
+		if (iet->et_epoch == epoch)
+			epoch_trace_report("Recursively entering epoch %s "
+			    "previously entered at %s:%d\n",
+			    epoch->e_name, iet->et_file, iet->et_line);
+	et->et_epoch = epoch;
+	et->et_file = file;
+	et->et_line = line;
+	SLIST_INSERT_HEAD(&td->td_epochs, et, et_tlink);
+}
+
+static inline void
+epoch_trace_exit(struct thread *td, epoch_t epoch, epoch_tracker_t et,
+    const char *file, int line)
+{
+
+	if (SLIST_FIRST(&td->td_epochs) != et) {
+		epoch_trace_report("Exiting epoch %s in a not nested order. "
+		    "Most recently entered %s at %s:%d\n",
+		    epoch->e_name,
+		    SLIST_FIRST(&td->td_epochs)->et_epoch->e_name,
+		    SLIST_FIRST(&td->td_epochs)->et_file,
+		    SLIST_FIRST(&td->td_epochs)->et_line);
+		/* This will panic if et is not anywhere on td_epochs. */
+		SLIST_REMOVE(&td->td_epochs, et, epoch_tracker, et_tlink);
+	} else
+		SLIST_REMOVE_HEAD(&td->td_epochs, et_tlink);
+}
+#endif /* EPOCH_TRACE */
+
 static void
 epoch_init(void *arg __unused)
 {
@@ -156,9 +258,10 @@ epoch_init(void *arg __unused)
 		    DPCPU_ID_PTR(cpu, epoch_cb_task), NULL, cpu, NULL, NULL,
 		    "epoch call task");
 	}
+	SLIST_INIT(&thread0.td_epochs);
 	inited = 1;
-	global_epoch = epoch_alloc(0);
-	global_epoch_preempt = epoch_alloc(EPOCH_PREEMPT);
+	global_epoch = epoch_alloc("Global", 0);
+	global_epoch_preempt = epoch_alloc("Global preemptible", EPOCH_PREEMPT);
 }
 SYSINIT(epoch, SI_SUB_TASKQ + 1, SI_ORDER_FIRST, epoch_init, NULL);
 
@@ -198,7 +301,7 @@ epoch_adjust_prio(struct thread *td, u_char prio)
 }
 
 epoch_t
-epoch_alloc(int flags)
+epoch_alloc(const char *name, int flags)
 {
 	epoch_t epoch;
 
@@ -210,6 +313,7 @@ epoch_alloc(int flags)
 	MPASS(epoch_count < MAX_EPOCHS - 2);
 	epoch->e_flags = flags;
 	epoch->e_idx = epoch_count;
+	epoch->e_name = name;
 	sx_init(&epoch->e_drain_sx, "epoch-drain-sx");
 	mtx_init(&epoch->e_drain_mtx, "epoch-drain-mtx", NULL, MTX_DEF);
 	allepochs[epoch_count++] = epoch;
@@ -243,7 +347,7 @@ epoch_currecord(epoch_t epoch)
 	} while (0)
 
 void
-epoch_enter_preempt(epoch_t epoch, epoch_tracker_t et)
+_epoch_enter_preempt(epoch_t epoch, epoch_tracker_t et EPOCH_FILE_LINE)
 {
 	struct epoch_record *er;
 	struct thread *td;
@@ -251,16 +355,14 @@ epoch_enter_preempt(epoch_t epoch, epoch_tracker_t et)
 	MPASS(cold || epoch != NULL);
 	INIT_CHECK(epoch);
 	MPASS(epoch->e_flags & EPOCH_PREEMPT);
-#ifdef EPOCH_TRACKER_DEBUG
-	et->et_magic_pre = EPOCH_MAGIC0;
-	et->et_magic_post = EPOCH_MAGIC1;
-#endif
 	td = curthread;
+#ifdef EPOCH_TRACE
+	epoch_trace_enter(td, epoch, et, file, line);
+#endif
 	et->et_td = td;
 	td->td_epochnest++;
 	critical_enter();
 	sched_pin();
-
 	td->td_pre_epoch_prio = td->td_priority;
 	er = epoch_currecord(epoch);
 	TAILQ_INSERT_TAIL(&er->er_tdlist, et, et_link);
@@ -277,7 +379,6 @@ epoch_enter(epoch_t epoch)
 	MPASS(cold || epoch != NULL);
 	INIT_CHECK(epoch);
 	td = curthread;
-
 	td->td_epochnest++;
 	critical_enter();
 	er = epoch_currecord(epoch);
@@ -285,7 +386,7 @@ epoch_enter(epoch_t epoch)
 }
 
 void
-epoch_exit_preempt(epoch_t epoch, epoch_tracker_t et)
+_epoch_exit_preempt(epoch_t epoch, epoch_tracker_t et EPOCH_FILE_LINE)
 {
 	struct epoch_record *er;
 	struct thread *td;
@@ -300,12 +401,6 @@ epoch_exit_preempt(epoch_t epoch, epoch_tracker_t et)
 	MPASS(epoch->e_flags & EPOCH_PREEMPT);
 	MPASS(et != NULL);
 	MPASS(et->et_td == td);
-#ifdef EPOCH_TRACKER_DEBUG
-	MPASS(et->et_magic_pre == EPOCH_MAGIC0);
-	MPASS(et->et_magic_post == EPOCH_MAGIC1);
-	et->et_magic_pre = 0;
-	et->et_magic_post = 0;
-#endif
 #ifdef INVARIANTS
 	et->et_td = (void*)0xDEADBEEF;
 #endif
@@ -315,6 +410,9 @@ epoch_exit_preempt(epoch_t epoch, epoch_tracker_t et)
 	if (__predict_false(td->td_pre_epoch_prio != td->td_priority))
 		epoch_adjust_prio(td, td->td_pre_epoch_prio);
 	critical_exit();
+#ifdef EPOCH_TRACE
+	epoch_trace_exit(td, epoch, et, file, line);
+#endif
 }
 
 void
diff --git a/sys/kern/subr_stack.c b/sys/kern/subr_stack.c
index 0429a5fb2434..0ec11e85e9a5 100644
--- a/sys/kern/subr_stack.c
+++ b/sys/kern/subr_stack.c
@@ -45,7 +45,7 @@ __FBSDID("$FreeBSD$");
 
 FEATURE(stack, "Support for capturing kernel stack");
 
-static MALLOC_DEFINE(M_STACK, "stack", "Stack Traces");
+MALLOC_DEFINE(M_STACK, "stack", "Stack Traces");
 
 static int stack_symbol(vm_offset_t pc, char *namebuf, u_int buflen,
 	    long *offset, int flags);
diff --git a/sys/net/if.c b/sys/net/if.c
index 8de83b2d7bc5..7e9f800593bc 100644
--- a/sys/net/if.c
+++ b/sys/net/if.c
@@ -940,8 +940,8 @@ static void
 if_epochalloc(void *dummy __unused)
 {
 
-	net_epoch_preempt = epoch_alloc(EPOCH_PREEMPT);
-	net_epoch = epoch_alloc(0);
+	net_epoch_preempt = epoch_alloc("Net preemptible", EPOCH_PREEMPT);
+	net_epoch = epoch_alloc("Net", 0);
 }
 SYSINIT(ifepochalloc, SI_SUB_TASKQ + 1, SI_ORDER_ANY,
     if_epochalloc, NULL);
diff --git a/sys/sys/epoch.h b/sys/sys/epoch.h
index 3078a53fedbf..4d7172dd91a9 100644
--- a/sys/sys/epoch.h
+++ b/sys/sys/epoch.h
@@ -41,6 +41,8 @@ typedef struct epoch_context *epoch_context_t;
 #include <sys/pcpu.h>
 #include <ck_epoch.h>
 
+#include "opt_epoch.h"
+
 struct epoch;
 typedef struct epoch *epoch_t;
 
@@ -51,21 +53,19 @@ extern epoch_t global_epoch;
 extern epoch_t global_epoch_preempt;
 
 struct epoch_tracker {
-#ifdef	EPOCH_TRACKER_DEBUG
-#define	EPOCH_MAGIC0 0xFADECAFEF00DD00D
-#define	EPOCH_MAGIC1 0xBADDBABEDEEDFEED
-	uint64_t et_magic_pre;
-#endif
 	TAILQ_ENTRY(epoch_tracker) et_link;
 	struct thread *et_td;
 	ck_epoch_section_t et_section;
-#ifdef	EPOCH_TRACKER_DEBUG
-	uint64_t et_magic_post;
+#ifdef EPOCH_TRACE
+	struct epoch *et_epoch;
+	SLIST_ENTRY(epoch_tracker) et_tlink;
+	const char *et_file;
+	int et_line;
 #endif
 }  __aligned(sizeof(void *));
 typedef struct epoch_tracker *epoch_tracker_t;
 
-epoch_t	epoch_alloc(int flags);
+epoch_t	epoch_alloc(const char *name, int flags);
 void	epoch_free(epoch_t epoch);
 void	epoch_wait(epoch_t epoch);
 void	epoch_wait_preempt(epoch_t epoch);
@@ -75,11 +75,22 @@ int	in_epoch(epoch_t epoch);
 int in_epoch_verbose(epoch_t epoch, int dump_onfail);
 DPCPU_DECLARE(int, epoch_cb_count);
 DPCPU_DECLARE(struct grouptask, epoch_cb_task);
-#define EPOCH_MAGIC0 0xFADECAFEF00DD00D
-#define EPOCH_MAGIC1 0xBADDBABEDEEDFEED
 
-void epoch_enter_preempt(epoch_t epoch, epoch_tracker_t et);
-void epoch_exit_preempt(epoch_t epoch, epoch_tracker_t et);
+#ifdef EPOCH_TRACE
+#define	EPOCH_FILE_LINE	, const char *file, int line
+#else
+#define	EPOCH_FILE_LINE
+#endif
+
+void _epoch_enter_preempt(epoch_t epoch, epoch_tracker_t et EPOCH_FILE_LINE);
+void _epoch_exit_preempt(epoch_t epoch, epoch_tracker_t et EPOCH_FILE_LINE);
+#ifdef EPOCH_TRACE
+#define	epoch_enter_preempt(epoch, et)	_epoch_enter_preempt(epoch, et, __FILE__, __LINE__)
+#define	epoch_exit_preempt(epoch, et)	_epoch_exit_preempt(epoch, et, __FILE__, __LINE__)
+#else
+#define epoch_enter_preempt(epoch, et)	_epoch_enter_preempt(epoch, et)
+#define	epoch_exit_preempt(epoch, et)	_epoch_exit_preempt(epoch, et)
+#endif
 void epoch_enter(epoch_t epoch);
 void epoch_exit(epoch_t epoch);
 
diff --git a/sys/sys/proc.h b/sys/sys/proc.h
index ae605a1266dd..8edca8ad889b 100644
--- a/sys/sys/proc.h
+++ b/sys/sys/proc.h
@@ -367,6 +367,7 @@ struct thread {
 	void		*td_lkpi_task;	/* LinuxKPI task struct pointer */
 	struct epoch_tracker *td_et;	/* (k) compat KPI spare tracker */
 	int		td_pmcpend;
+	SLIST_HEAD(, epoch_tracker) td_epochs;
 };
 
 struct thread0_storage {
diff --git a/sys/sys/stack.h b/sys/sys/stack.h
index 3b4eff8ab117..03a7dbfb3c97 100644
--- a/sys/sys/stack.h
+++ b/sys/sys/stack.h
@@ -33,6 +33,10 @@
 
 #include <sys/_stack.h>
 
+#ifdef _SYS_MALLOC_H_
+MALLOC_DECLARE(M_STACK);
+#endif
+
 struct sbuf;
 
 /* MI Routines. */