[PATCH RT 3/8] mm: slab: Fix potential deadlock

Steven Rostedt
2012-10-12T01:21:41Z

[-- Attachment #1: 0003-mm-slab-Fix-potential-deadlock.patch --]
[-- Type: text/plain, Size: 3517 bytes --]

From: Thomas Gleixner <tglx@linutronix.de>

=============================================
[ INFO: possible recursive locking detected ]
3.6.0-rt1+ #49 Not tainted
---------------------------------------------
swapper/0/1 is trying to acquire lock:
lock_slab_on+0x72/0x77

but task is already holding lock:
__local_lock_irq+0x24/0x77

other info that might help us debug this:
Possible unsafe locking scenario:

CPU0
----
lock(&per_cpu(slab_lock, __cpu).lock);
lock(&per_cpu(slab_lock, __cpu).lock);

*** DEADLOCK ***

May be due to missing lock nesting notation

2 locks held by swapper/0/1:
kmem_cache_create+0x33/0x89
__local_lock_irq+0x24/0x77

stack backtrace:
Pid: 1, comm: swapper/0 Not tainted 3.6.0-rt1+ #49
Call Trace:
__lock_acquire+0x9a4/0xdc4
? __local_lock_irq+0x24/0x77
? lock_slab_on+0x72/0x77
lock_acquire+0xc4/0x108
? lock_slab_on+0x72/0x77
? unlock_slab_on+0x5b/0x5b
rt_spin_lock+0x36/0x3d
? lock_slab_on+0x72/0x77
? migrate_disable+0x85/0x93
lock_slab_on+0x72/0x77
do_ccupdate_local+0x19/0x44
slab_on_each_cpu+0x36/0x5a
do_tune_cpucache+0xc1/0x305
enable_cpucache+0x8c/0xb5
setup_cpu_cache+0x28/0x182
__kmem_cache_create+0x34b/0x380
? shmem_mount+0x1a/0x1a
kmem_cache_create+0x4a/0x89
? shmem_mount+0x1a/0x1a
shmem_init+0x3e/0xd4
kernel_init+0x11c/0x214
kernel_thread_helper+0x4/0x10
? retint_restore_args+0x13/0x13
? start_kernel+0x3bc/0x3bc
? gs_change+0x13/0x13

It's not a missing annotation. It's simply wrong code and needs to be
fixed. Instead of nesting the local and the remote cpu lock simply
acquire only the remote cpu lock, which is sufficient protection for
this procedure.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: stable-rt@vger.kernel.org
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
---
include/linux/locallock.h | 8 ++++++++
mm/slab.c | 10 ++--------
2 files changed, 10 insertions(+), 8 deletions(-)

diff --git a/include/linux/locallock.h b/include/linux/locallock.h
index 8fbc393..0161fbb 100644
--- a/include/linux/locallock.h
+++ b/include/linux/locallock.h
@@ -96,6 +96,9 @@ static inline void __local_lock_irq(struct local_irq_lock *lv)
#define local_lock_irq(lvar) \
do { __local_lock_irq(&get_local_var(lvar)); } while (0)

+#define local_lock_irq_on(lvar, cpu) \
+ do { __local_lock_irq(&per_cpu(lvar, cpu)); } while (0)
+
static inline void __local_unlock_irq(struct local_irq_lock *lv)
{
LL_WARN(!lv->nestcnt);
@@ -111,6 +114,11 @@ static inline void __local_unlock_irq(struct local_irq_lock *lv)
put_local_var(lvar); \
} while (0)

+#define local_unlock_irq_on(lvar, cpu) \
+ do { \
+ __local_unlock_irq(&per_cpu(lvar, cpu)); \
+ } while (0)
+
static inline int __local_lock_irqsave(struct local_irq_lock *lv)
{
if (lv->owner != current) {
diff --git a/mm/slab.c b/mm/slab.c
index 411c545..6a8fd1b 100644
--- a/mm/slab.c
+++ b/mm/slab.c
@@ -747,18 +747,12 @@ slab_on_each_cpu(void (*func)(void *arg, int this_cpu), void *arg)

static void lock_slab_on(unsigned int cpu)
{
- if (cpu == smp_processor_id())
- local_lock_irq(slab_lock);
- else
- local_spin_lock_irq(slab_lock, &per_cpu(slab_lock, cpu).lock);
+ local_lock_irq_on(slab_lock, cpu);
}

static void unlock_slab_on(unsigned int cpu)
{
- if (cpu == smp_processor_id())
- local_unlock_irq(slab_lock);
- else
- local_spin_unlock_irq(slab_lock, &per_cpu(slab_lock, cpu).lock);
+ local_unlock_irq_on(slab_lock, cpu);
}
#endif

--
1.7.10.4