Merge branch 'for-mingo' of git://git.kernel.org/pub/scm/linux/kernel/git/paulmck/linux-rcu into core/rcu

Pull RCU updates from Paul E. McKenney:

 - Documentation updates, yet again just simple changes.

 - Miscellaneous fixes, including a change to call_rcu()'s
   rcu_head alignment check.

 - Security-motivated list consistency checks, which are
   disabled by default behind DEBUG_LIST.

 - Torture-test updates.

Signed-off-by: Ingo Molnar <mingo@kernel.org>

2 files changed, 42 insertions, 72 deletions

diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug
index a6c8db1d62f6..9bb7d825ba14 100644
--- a/lib/Kconfig.debug
+++ b/lib/Kconfig.debug
@@ -1218,7 +1218,7 @@ config DEBUG_BUGVERBOSE
 
 config DEBUG_LIST
 	bool "Debug linked list manipulation"
-	depends on DEBUG_KERNEL
+	depends on DEBUG_KERNEL || BUG_ON_DATA_CORRUPTION
 	help
 	  Enable this to turn on extended checks in the linked-list
 	  walking routines.
@@ -1434,7 +1434,8 @@ config RCU_TRACE
 	select TRACE_CLOCK
 	help
 	  This option provides tracing in RCU which presents stats
-	  in debugfs for debugging RCU implementation.
+	  in debugfs for debugging RCU implementation.  It also enables
+	  additional tracepoints for ftrace-style event tracing.
 
 	  Say Y here if you want to enable RCU tracing
 	  Say N if you are unsure.
@@ -1964,6 +1965,16 @@ config TEST_STATIC_KEYS
 
 	  If unsure, say N.
 
+config BUG_ON_DATA_CORRUPTION
+	bool "Trigger a BUG when data corruption is detected"
+	select DEBUG_LIST
+	help
+	  Select this option if the kernel should BUG when it encounters
+	  data corruption in kernel memory structures when they get checked
+	  for validity.
+
+	  If unsure, say N.
+
 source "samples/Kconfig"
 
 source "lib/Kconfig.kgdb"
diff --git a/lib/list_debug.c b/lib/list_debug.c
index 3859bf63561c..7f7bfa55eb6d 100644
--- a/lib/list_debug.c
+++ b/lib/list_debug.c
@@ -2,8 +2,7 @@
  * Copyright 2006, Red Hat, Inc., Dave Jones
  * Released under the General Public License (GPL).
  *
- * This file contains the linked list implementations for
- * DEBUG_LIST.
+ * This file contains the linked list validation for DEBUG_LIST.
  */
 
 #include <linux/export.h>
@@ -13,88 +12,48 @@
 #include <linux/rculist.h>
 
 /*
- * Insert a new entry between two known consecutive entries.
- *
- * This is only for internal list manipulation where we know
- * the prev/next entries already!
+ * Check that the data structures for the list manipulations are reasonably
+ * valid. Failures here indicate memory corruption (and possibly an exploit
+ * attempt).
  */
 
-void __list_add(struct list_head *new,
-			      struct list_head *prev,
-			      struct list_head *next)
+bool __list_add_valid(struct list_head *new, struct list_head *prev,
+		      struct list_head *next)
 {
-	WARN(next->prev != prev,
-		"list_add corruption. next->prev should be "
-		"prev (%p), but was %p. (next=%p).\n",
+	CHECK_DATA_CORRUPTION(next->prev != prev,
+		"list_add corruption. next->prev should be prev (%p), but was %p. (next=%p).\n",
 		prev, next->prev, next);
-	WARN(prev->next != next,
-		"list_add corruption. prev->next should be "
-		"next (%p), but was %p. (prev=%p).\n",
+	CHECK_DATA_CORRUPTION(prev->next != next,
+		"list_add corruption. prev->next should be next (%p), but was %p. (prev=%p).\n",
 		next, prev->next, prev);
-	WARN(new == prev || new == next,
-	     "list_add double add: new=%p, prev=%p, next=%p.\n",
-	     new, prev, next);
-	next->prev = new;
-	new->next = next;
-	new->prev = prev;
-	WRITE_ONCE(prev->next, new);
+	CHECK_DATA_CORRUPTION(new == prev || new == next,
+		"list_add double add: new=%p, prev=%p, next=%p.\n",
+		new, prev, next);
+
+	return true;
 }
-EXPORT_SYMBOL(__list_add);
+EXPORT_SYMBOL(__list_add_valid);
 
-void __list_del_entry(struct list_head *entry)
+bool __list_del_entry_valid(struct list_head *entry)
 {
 	struct list_head *prev, *next;
 
 	prev = entry->prev;
 	next = entry->next;
 
-	if (WARN(next == LIST_POISON1,
+	CHECK_DATA_CORRUPTION(next == LIST_POISON1,
 		"list_del corruption, %p->next is LIST_POISON1 (%p)\n",
-		entry, LIST_POISON1) ||
-	    WARN(prev == LIST_POISON2,
+		entry, LIST_POISON1);
+	CHECK_DATA_CORRUPTION(prev == LIST_POISON2,
 		"list_del corruption, %p->prev is LIST_POISON2 (%p)\n",
-		entry, LIST_POISON2) ||
-	    WARN(prev->next != entry,
-		"list_del corruption. prev->next should be %p, "
-		"but was %p\n", entry, prev->next) ||
-	    WARN(next->prev != entry,
-		"list_del corruption. next->prev should be %p, "
-		"but was %p\n", entry, next->prev))
-		return;
-
-	__list_del(prev, next);
-}
-EXPORT_SYMBOL(__list_del_entry);
+		entry, LIST_POISON2);
+	CHECK_DATA_CORRUPTION(prev->next != entry,
+		"list_del corruption. prev->next should be %p, but was %p\n",
+		entry, prev->next);
+	CHECK_DATA_CORRUPTION(next->prev != entry,
+		"list_del corruption. next->prev should be %p, but was %p\n",
+		entry, next->prev);
+	return true;
 
-/**
- * list_del - deletes entry from list.
- * @entry: the element to delete from the list.
- * Note: list_empty on entry does not return true after this, the entry is
- * in an undefined state.
- */
-void list_del(struct list_head *entry)
-{
-	__list_del_entry(entry);
-	entry->next = LIST_POISON1;
-	entry->prev = LIST_POISON2;
-}
-EXPORT_SYMBOL(list_del);
-
-/*
- * RCU variants.
- */
-void __list_add_rcu(struct list_head *new,
-		    struct list_head *prev, struct list_head *next)
-{
-	WARN(next->prev != prev,
-		"list_add_rcu corruption. next->prev should be prev (%p), but was %p. (next=%p).\n",
-		prev, next->prev, next);
-	WARN(prev->next != next,
-		"list_add_rcu corruption. prev->next should be next (%p), but was %p. (prev=%p).\n",
-		next, prev->next, prev);
-	new->next = next;
-	new->prev = prev;
-	rcu_assign_pointer(list_next_rcu(prev), new);
-	next->prev = new;
 }
-EXPORT_SYMBOL(__list_add_rcu);
+EXPORT_SYMBOL(__list_del_entry_valid);