[PATCH] pi-futex: rt mutex debug

Runtime debugging functionality for rt-mutexes.

Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Arjan van de Ven <arjan@linux.intel.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

8 files changed, 581 insertions, 1 deletions

diff --git a/include/linux/mm.h b/include/linux/mm.h
index 0ac255720f34..c41a1299b8cf 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -1034,6 +1034,7 @@ static inline void
 debug_check_no_locks_freed(const void *from, unsigned long len)
 {
         mutex_debug_check_no_locks_freed(from, len);
+        rt_mutex_debug_check_no_locks_freed(from, len);
 }
 
 #ifndef CONFIG_DEBUG_PAGEALLOC
diff --git a/include/linux/rtmutex.h b/include/linux/rtmutex.h
index 12309c916c68..fa4a3b82ba70 100644
--- a/include/linux/rtmutex.h
+++ b/include/linux/rtmutex.h
@@ -41,6 +41,19 @@ struct rt_mutex_waiter;
 struct hrtimer_sleeper;
 
 #ifdef CONFIG_DEBUG_RT_MUTEXES
+ extern int rt_mutex_debug_check_no_locks_freed(const void *from,
+                                                unsigned long len);
+ extern void rt_mutex_debug_check_no_locks_held(struct task_struct *task);
+#else
+ static inline int rt_mutex_debug_check_no_locks_freed(const void *from,
+                                                       unsigned long len)
+ {
+        return 0;
+ }
+# define rt_mutex_debug_check_no_locks_held(task)       do { } while (0)
+#endif
+
+#ifdef CONFIG_DEBUG_RT_MUTEXES
 # define __DEBUG_RT_MUTEX_INITIALIZER(mutexname) \
         , .name = #mutexname, .file = __FILE__, .line = __LINE__
 # define rt_mutex_init(mutex)                   __rt_mutex_init(mutex, __FUNCTION__)
@@ -48,7 +61,7 @@ struct hrtimer_sleeper;
 #else
 # define __DEBUG_RT_MUTEX_INITIALIZER(mutexname)
 # define rt_mutex_init(mutex)                   __rt_mutex_init(mutex, NULL)
-# define rt_mutex_debug_task_free(t)            do { } while (0)
+# define rt_mutex_debug_task_free(t)                    do { } while (0)
 #endif
 
 #define __RT_MUTEX_INITIALIZER(mutexname) \
diff --git a/kernel/Makefile b/kernel/Makefile
index 21df9a338ff0..f9c92d34cde5 100644
--- a/kernel/Makefile
+++ b/kernel/Makefile
@@ -17,6 +17,7 @@ ifeq ($(CONFIG_COMPAT),y)
 obj-$(CONFIG_FUTEX) += futex_compat.o
 endif
 obj-$(CONFIG_RT_MUTEXES) += rtmutex.o
+obj-$(CONFIG_DEBUG_RT_MUTEXES) += rtmutex-debug.o
 obj-$(CONFIG_GENERIC_ISA_DMA) += dma.o
 obj-$(CONFIG_SMP) += cpu.o spinlock.o
 obj-$(CONFIG_DEBUG_SPINLOCK) += spinlock.o
diff --git a/kernel/exit.c b/kernel/exit.c
index 304ef637be6c..3e8a0282e9a5 100644
--- a/kernel/exit.c
+++ b/kernel/exit.c
@@ -929,6 +929,7 @@ fastcall NORET_TYPE void do_exit(long code)
          * If DEBUG_MUTEXES is on, make sure we are holding no locks:
          */
         mutex_debug_check_no_locks_held(tsk);
+        rt_mutex_debug_check_no_locks_held(tsk);
 
         if (tsk->io_context)
                 exit_io_context();
diff --git a/kernel/rtmutex-debug.c b/kernel/rtmutex-debug.c
new file mode 100644
index 000000000000..4aa8a2c9f453
--- /dev/null
+++ b/kernel/rtmutex-debug.c
@@ -0,0 +1,513 @@
+/*
+ * RT-Mutexes: blocking mutual exclusion locks with PI support
+ *
+ * started by Ingo Molnar and Thomas Gleixner:
+ *
+ *  Copyright (C) 2004-2006 Red Hat, Inc., Ingo Molnar <mingo@redhat.com>
+ *  Copyright (C) 2006 Timesys Corp., Thomas Gleixner <tglx@timesys.com>
+ *
+ * This code is based on the rt.c implementation in the preempt-rt tree.
+ * Portions of said code are
+ *
+ *  Copyright (C) 2004  LynuxWorks, Inc., Igor Manyilov, Bill Huey
+ *  Copyright (C) 2006  Esben Nielsen
+ *  Copyright (C) 2006  Kihon Technologies Inc.,
+ *                      Steven Rostedt <rostedt@goodmis.org>
+ *
+ * See rt.c in preempt-rt for proper credits and further information
+ */
+#include <linux/config.h>
+#include <linux/sched.h>
+#include <linux/delay.h>
+#include <linux/module.h>
+#include <linux/spinlock.h>
+#include <linux/kallsyms.h>
+#include <linux/syscalls.h>
+#include <linux/interrupt.h>
+#include <linux/plist.h>
+#include <linux/fs.h>
+
+#include "rtmutex_common.h"
+
+#ifdef CONFIG_DEBUG_RT_MUTEXES
+# include "rtmutex-debug.h"
+#else
+# include "rtmutex.h"
+#endif
+
+# define TRACE_WARN_ON(x)                       WARN_ON(x)
+# define TRACE_BUG_ON(x)                        BUG_ON(x)
+
+# define TRACE_OFF()                                            \
+do {                                                            \
+        if (rt_trace_on) {                                      \
+                rt_trace_on = 0;                                \
+                console_verbose();                              \
+                if (spin_is_locked(&current->pi_lock))          \
+                        spin_unlock(&current->pi_lock);         \
+                if (spin_is_locked(&current->held_list_lock))   \
+                        spin_unlock(&current->held_list_lock);  \
+        }                                                       \
+} while (0)
+
+# define TRACE_OFF_NOLOCK()                                     \
+do {                                                            \
+        if (rt_trace_on) {                                      \
+                rt_trace_on = 0;                                \
+                console_verbose();                              \
+        }                                                       \
+} while (0)
+
+# define TRACE_BUG_LOCKED()                     \
+do {                                            \
+        TRACE_OFF();                            \
+        BUG();                                  \
+} while (0)
+
+# define TRACE_WARN_ON_LOCKED(c)                \
+do {                                            \
+        if (unlikely(c)) {                      \
+                TRACE_OFF();                    \
+                WARN_ON(1);                     \
+        }                                       \
+} while (0)
+
+# define TRACE_BUG_ON_LOCKED(c)                 \
+do {                                            \
+        if (unlikely(c))                        \
+                TRACE_BUG_LOCKED();             \
+} while (0)
+
+#ifdef CONFIG_SMP
+# define SMP_TRACE_BUG_ON_LOCKED(c)     TRACE_BUG_ON_LOCKED(c)
+#else
+# define SMP_TRACE_BUG_ON_LOCKED(c)     do { } while (0)
+#endif
+
+/*
+ * deadlock detection flag. We turn it off when we detect
+ * the first problem because we dont want to recurse back
+ * into the tracing code when doing error printk or
+ * executing a BUG():
+ */
+int rt_trace_on = 1;
+
+void deadlock_trace_off(void)
+{
+        rt_trace_on = 0;
+}
+
+static void printk_task(task_t *p)
+{
+        if (p)
+                printk("%16s:%5d [%p, %3d]", p->comm, p->pid, p, p->prio);
+        else
+                printk("<none>");
+}
+
+static void printk_task_short(task_t *p)
+{
+        if (p)
+                printk("%s/%d [%p, %3d]", p->comm, p->pid, p, p->prio);
+        else
+                printk("<none>");
+}
+
+static void printk_lock(struct rt_mutex *lock, int print_owner)
+{
+        if (lock->name)
+                printk(" [%p] {%s}\n",
+                        lock, lock->name);
+        else
+                printk(" [%p] {%s:%d}\n",
+                        lock, lock->file, lock->line);
+
+        if (print_owner && rt_mutex_owner(lock)) {
+                printk(".. ->owner: %p\n", lock->owner);
+                printk(".. held by:  ");
+                printk_task(rt_mutex_owner(lock));
+                printk("\n");
+        }
+        if (rt_mutex_owner(lock)) {
+                printk("... acquired at:               ");
+                print_symbol("%s\n", lock->acquire_ip);
+        }
+}
+
+static void printk_waiter(struct rt_mutex_waiter *w)
+{
+        printk("-------------------------\n");
+        printk("| waiter struct %p:\n", w);
+        printk("| w->list_entry: [DP:%p/%p|SP:%p/%p|PRI:%d]\n",
+               w->list_entry.plist.prio_list.prev, w->list_entry.plist.prio_list.next,
+               w->list_entry.plist.node_list.prev, w->list_entry.plist.node_list.next,
+               w->list_entry.prio);
+        printk("| w->pi_list_entry: [DP:%p/%p|SP:%p/%p|PRI:%d]\n",
+               w->pi_list_entry.plist.prio_list.prev, w->pi_list_entry.plist.prio_list.next,
+               w->pi_list_entry.plist.node_list.prev, w->pi_list_entry.plist.node_list.next,
+               w->pi_list_entry.prio);
+        printk("\n| lock:\n");
+        printk_lock(w->lock, 1);
+        printk("| w->ti->task:\n");
+        printk_task(w->task);
+        printk("| blocked at:  ");
+        print_symbol("%s\n", w->ip);
+        printk("-------------------------\n");
+}
+
+static void show_task_locks(task_t *p)
+{
+        switch (p->state) {
+        case TASK_RUNNING:              printk("R"); break;
+        case TASK_INTERRUPTIBLE:        printk("S"); break;
+        case TASK_UNINTERRUPTIBLE:      printk("D"); break;
+        case TASK_STOPPED:              printk("T"); break;
+        case EXIT_ZOMBIE:               printk("Z"); break;
+        case EXIT_DEAD:                 printk("X"); break;
+        default:                        printk("?"); break;
+        }
+        printk_task(p);
+        if (p->pi_blocked_on) {
+                struct rt_mutex *lock = p->pi_blocked_on->lock;
+
+                printk(" blocked on:");
+                printk_lock(lock, 1);
+        } else
+                printk(" (not blocked)\n");
+}
+
+void rt_mutex_show_held_locks(task_t *task, int verbose)
+{
+        struct list_head *curr, *cursor = NULL;
+        struct rt_mutex *lock;
+        task_t *t;
+        unsigned long flags;
+        int count = 0;
+
+        if (!rt_trace_on)
+                return;
+
+        if (verbose) {
+                printk("------------------------------\n");
+                printk("| showing all locks held by: |  (");
+                printk_task_short(task);
+                printk("):\n");
+                printk("------------------------------\n");
+        }
+
+next:
+        spin_lock_irqsave(&task->held_list_lock, flags);
+        list_for_each(curr, &task->held_list_head) {
+                if (cursor && curr != cursor)
+                        continue;
+                lock = list_entry(curr, struct rt_mutex, held_list_entry);
+                t = rt_mutex_owner(lock);
+                WARN_ON(t != task);
+                count++;
+                cursor = curr->next;
+                spin_unlock_irqrestore(&task->held_list_lock, flags);
+
+                printk("\n#%03d:            ", count);
+                printk_lock(lock, 0);
+                goto next;
+        }
+        spin_unlock_irqrestore(&task->held_list_lock, flags);
+
+        printk("\n");
+}
+
+void rt_mutex_show_all_locks(void)
+{
+        task_t *g, *p;
+        int count = 10;
+        int unlock = 1;
+
+        printk("\n");
+        printk("----------------------\n");
+        printk("| showing all tasks: |\n");
+        printk("----------------------\n");
+
+        /*
+         * Here we try to get the tasklist_lock as hard as possible,
+         * if not successful after 2 seconds we ignore it (but keep
+         * trying). This is to enable a debug printout even if a
+         * tasklist_lock-holding task deadlocks or crashes.
+         */
+retry:
+        if (!read_trylock(&tasklist_lock)) {
+                if (count == 10)
+                        printk("hm, tasklist_lock locked, retrying... ");
+                if (count) {
+                        count--;
+                        printk(" #%d", 10-count);
+                        mdelay(200);
+                        goto retry;
+                }
+                printk(" ignoring it.\n");
+                unlock = 0;
+        }
+        if (count != 10)
+                printk(" locked it.\n");
+
+        do_each_thread(g, p) {
+                show_task_locks(p);
+                if (!unlock)
+                        if (read_trylock(&tasklist_lock))
+                                unlock = 1;
+        } while_each_thread(g, p);
+
+        printk("\n");
+
+        printk("-----------------------------------------\n");
+        printk("| showing all locks held in the system: |\n");
+        printk("-----------------------------------------\n");
+
+        do_each_thread(g, p) {
+                rt_mutex_show_held_locks(p, 0);
+                if (!unlock)
+                        if (read_trylock(&tasklist_lock))
+                                unlock = 1;
+        } while_each_thread(g, p);
+
+
+        printk("=============================================\n\n");
+
+        if (unlock)
+                read_unlock(&tasklist_lock);
+}
+
+void rt_mutex_debug_check_no_locks_held(task_t *task)
+{
+        struct rt_mutex_waiter *w;
+        struct list_head *curr;
+        struct rt_mutex *lock;
+
+        if (!rt_trace_on)
+                return;
+        if (!rt_prio(task->normal_prio) && rt_prio(task->prio)) {
+                printk("BUG: PI priority boost leaked!\n");
+                printk_task(task);
+                printk("\n");
+        }
+        if (list_empty(&task->held_list_head))
+                return;
+
+        spin_lock(&task->pi_lock);
+        plist_for_each_entry(w, &task->pi_waiters, pi_list_entry) {
+                TRACE_OFF();
+
+                printk("hm, PI interest held at exit time? Task:\n");
+                printk_task(task);
+                printk_waiter(w);
+                return;
+        }
+        spin_unlock(&task->pi_lock);
+
+        list_for_each(curr, &task->held_list_head) {
+                lock = list_entry(curr, struct rt_mutex, held_list_entry);
+
+                printk("BUG: %s/%d, lock held at task exit time!\n",
+                       task->comm, task->pid);
+                printk_lock(lock, 1);
+                if (rt_mutex_owner(lock) != task)
+                        printk("exiting task is not even the owner??\n");
+        }
+}
+
+int rt_mutex_debug_check_no_locks_freed(const void *from, unsigned long len)
+{
+        const void *to = from + len;
+        struct list_head *curr;
+        struct rt_mutex *lock;
+        unsigned long flags;
+        void *lock_addr;
+
+        if (!rt_trace_on)
+                return 0;
+
+        spin_lock_irqsave(&current->held_list_lock, flags);
+        list_for_each(curr, &current->held_list_head) {
+                lock = list_entry(curr, struct rt_mutex, held_list_entry);
+                lock_addr = lock;
+                if (lock_addr < from || lock_addr >= to)
+                        continue;
+                TRACE_OFF();
+
+                printk("BUG: %s/%d, active lock [%p(%p-%p)] freed!\n",
+                        current->comm, current->pid, lock, from, to);
+                dump_stack();
+                printk_lock(lock, 1);
+                if (rt_mutex_owner(lock) != current)
+                        printk("freeing task is not even the owner??\n");
+                return 1;
+        }
+        spin_unlock_irqrestore(&current->held_list_lock, flags);
+
+        return 0;
+}
+
+void rt_mutex_debug_task_free(struct task_struct *task)
+{
+        WARN_ON(!plist_head_empty(&task->pi_waiters));
+        WARN_ON(task->pi_blocked_on);
+}
+
+/*
+ * We fill out the fields in the waiter to store the information about
+ * the deadlock. We print when we return. act_waiter can be NULL in
+ * case of a remove waiter operation.
+ */
+void debug_rt_mutex_deadlock(int detect, struct rt_mutex_waiter *act_waiter,
+                             struct rt_mutex *lock)
+{
+        struct task_struct *task;
+
+        if (!rt_trace_on || detect || !act_waiter)
+                return;
+
+        task = rt_mutex_owner(act_waiter->lock);
+        if (task && task != current) {
+                act_waiter->deadlock_task_pid = task->pid;
+                act_waiter->deadlock_lock = lock;
+        }
+}
+
+void debug_rt_mutex_print_deadlock(struct rt_mutex_waiter *waiter)
+{
+        struct task_struct *task;
+
+        if (!waiter->deadlock_lock || !rt_trace_on)
+                return;
+
+        task = find_task_by_pid(waiter->deadlock_task_pid);
+        if (!task)
+                return;
+
+        TRACE_OFF_NOLOCK();
+
+        printk("\n============================================\n");
+        printk(  "[ BUG: circular locking deadlock detected! ]\n");
+        printk(  "--------------------------------------------\n");
+        printk("%s/%d is deadlocking current task %s/%d\n\n",
+               task->comm, task->pid, current->comm, current->pid);
+
+        printk("\n1) %s/%d is trying to acquire this lock:\n",
+               current->comm, current->pid);
+        printk_lock(waiter->lock, 1);
+
+        printk("... trying at:                 ");
+        print_symbol("%s\n", waiter->ip);
+
+        printk("\n2) %s/%d is blocked on this lock:\n", task->comm, task->pid);
+        printk_lock(waiter->deadlock_lock, 1);
+
+        rt_mutex_show_held_locks(current, 1);
+        rt_mutex_show_held_locks(task, 1);
+
+        printk("\n%s/%d's [blocked] stackdump:\n\n", task->comm, task->pid);
+        show_stack(task, NULL);
+        printk("\n%s/%d's [current] stackdump:\n\n",
+               current->comm, current->pid);
+        dump_stack();
+        rt_mutex_show_all_locks();
+        printk("[ turning off deadlock detection."
+               "Please report this trace. ]\n\n");
+        local_irq_disable();
+}
+
+void debug_rt_mutex_lock(struct rt_mutex *lock __IP_DECL__)
+{
+        unsigned long flags;
+
+        if (rt_trace_on) {
+                TRACE_WARN_ON_LOCKED(!list_empty(&lock->held_list_entry));
+
+                spin_lock_irqsave(&current->held_list_lock, flags);
+                list_add_tail(&lock->held_list_entry, &current->held_list_head);
+                spin_unlock_irqrestore(&current->held_list_lock, flags);
+
+                lock->acquire_ip = ip;
+        }
+}
+
+void debug_rt_mutex_unlock(struct rt_mutex *lock)
+{
+        unsigned long flags;
+
+        if (rt_trace_on) {
+                TRACE_WARN_ON_LOCKED(rt_mutex_owner(lock) != current);
+                TRACE_WARN_ON_LOCKED(list_empty(&lock->held_list_entry));
+
+                spin_lock_irqsave(&current->held_list_lock, flags);
+                list_del_init(&lock->held_list_entry);
+                spin_unlock_irqrestore(&current->held_list_lock, flags);
+        }
+}
+
+void debug_rt_mutex_proxy_lock(struct rt_mutex *lock,
+                               struct task_struct *powner __IP_DECL__)
+{
+        unsigned long flags;
+
+        if (rt_trace_on) {
+                TRACE_WARN_ON_LOCKED(!list_empty(&lock->held_list_entry));
+
+                spin_lock_irqsave(&powner->held_list_lock, flags);
+                list_add_tail(&lock->held_list_entry, &powner->held_list_head);
+                spin_unlock_irqrestore(&powner->held_list_lock, flags);
+
+                lock->acquire_ip = ip;
+        }
+}
+
+void debug_rt_mutex_proxy_unlock(struct rt_mutex *lock)
+{
+        unsigned long flags;
+
+        if (rt_trace_on) {
+                struct task_struct *owner = rt_mutex_owner(lock);
+
+                TRACE_WARN_ON_LOCKED(!owner);
+                TRACE_WARN_ON_LOCKED(list_empty(&lock->held_list_entry));
+
+                spin_lock_irqsave(&owner->held_list_lock, flags);
+                list_del_init(&lock->held_list_entry);
+                spin_unlock_irqrestore(&owner->held_list_lock, flags);
+        }
+}
+
+void debug_rt_mutex_init_waiter(struct rt_mutex_waiter *waiter)
+{
+        memset(waiter, 0x11, sizeof(*waiter));
+        plist_node_init(&waiter->list_entry, MAX_PRIO);
+        plist_node_init(&waiter->pi_list_entry, MAX_PRIO);
+}
+
+void debug_rt_mutex_free_waiter(struct rt_mutex_waiter *waiter)
+{
+        TRACE_WARN_ON(!plist_node_empty(&waiter->list_entry));
+        TRACE_WARN_ON(!plist_node_empty(&waiter->pi_list_entry));
+        TRACE_WARN_ON(waiter->task);
+        memset(waiter, 0x22, sizeof(*waiter));
+}
+
+void debug_rt_mutex_init(struct rt_mutex *lock, const char *name)
+{
+        void *addr = lock;
+
+        if (rt_trace_on) {
+                rt_mutex_debug_check_no_locks_freed(addr,
+                                                    sizeof(struct rt_mutex));
+                INIT_LIST_HEAD(&lock->held_list_entry);
+                lock->name = name;
+        }
+}
+
+void rt_mutex_deadlock_account_lock(struct rt_mutex *lock, task_t *task)
+{
+}
+
+void rt_mutex_deadlock_account_unlock(struct task_struct *task)
+{
+}
+
diff --git a/kernel/rtmutex-debug.h b/kernel/rtmutex-debug.h
new file mode 100644
index 000000000000..7612fbc62d70
--- /dev/null
+++ b/kernel/rtmutex-debug.h
@@ -0,0 +1,37 @@
+/*
+ * RT-Mutexes: blocking mutual exclusion locks with PI support
+ *
+ * started by Ingo Molnar and Thomas Gleixner:
+ *
+ *  Copyright (C) 2004-2006 Red Hat, Inc., Ingo Molnar <mingo@redhat.com>
+ *  Copyright (C) 2006, Timesys Corp., Thomas Gleixner <tglx@timesys.com>
+ *
+ * This file contains macros used solely by rtmutex.c. Debug version.
+ */
+
+#define __IP_DECL__             , unsigned long ip
+#define __IP__                  , ip
+#define __RET_IP__              , (unsigned long)__builtin_return_address(0)
+
+extern void
+rt_mutex_deadlock_account_lock(struct rt_mutex *lock, struct task_struct *task);
+extern void rt_mutex_deadlock_account_unlock(struct task_struct *task);
+extern void debug_rt_mutex_init_waiter(struct rt_mutex_waiter *waiter);
+extern void debug_rt_mutex_free_waiter(struct rt_mutex_waiter *waiter);
+extern void debug_rt_mutex_init(struct rt_mutex *lock, const char *name);
+extern void debug_rt_mutex_lock(struct rt_mutex *lock __IP_DECL__);
+extern void debug_rt_mutex_unlock(struct rt_mutex *lock);
+extern void debug_rt_mutex_proxy_lock(struct rt_mutex *lock,
+                                      struct task_struct *powner __IP_DECL__);
+extern void debug_rt_mutex_proxy_unlock(struct rt_mutex *lock);
+extern void debug_rt_mutex_deadlock(int detect, struct rt_mutex_waiter *waiter,
+                                    struct rt_mutex *lock);
+extern void debug_rt_mutex_print_deadlock(struct rt_mutex_waiter *waiter);
+# define debug_rt_mutex_reset_waiter(w)                 \
+        do { (w)->deadlock_lock = NULL; } while (0)
+
+static inline int debug_rt_mutex_detect_deadlock(struct rt_mutex_waiter *waiter,
+                                                 int detect)
+{
+        return (waiter != NULL);
+}
diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug
index 8bab0102ac73..06d3ea1133c9 100644
--- a/lib/Kconfig.debug
+++ b/lib/Kconfig.debug
@@ -107,6 +107,19 @@ config DEBUG_MUTEXES
          This allows mutex semantics violations and mutex related deadlocks
          (lockups) to be detected and reported automatically.
 
+config DEBUG_RT_MUTEXES
+        bool "RT Mutex debugging, deadlock detection"
+        default y
+        depends on DEBUG_KERNEL && RT_MUTEXES
+        help
+         This allows rt mutex semantics violations and rt mutex related
+         deadlocks (lockups) to be detected and reported automatically.
+
+config DEBUG_PI_LIST
+        bool
+        default y
+        depends on DEBUG_RT_MUTEXES
+
 config DEBUG_SPINLOCK
         bool "Spinlock debugging"
         depends on DEBUG_KERNEL
diff --git a/mm/slab.c b/mm/slab.c
index f378d027c684..233e39d14caf 100644
--- a/mm/slab.c
+++ b/mm/slab.c
@@ -107,6 +107,7 @@
 #include        <linux/nodemask.h>
 #include        <linux/mempolicy.h>
 #include        <linux/mutex.h>
+#include        <linux/rtmutex.h>
 
 #include        <asm/uaccess.h>
 #include        <asm/cacheflush.h>