Commit 1f8a6a10 authored by Peter Zijlstra's avatar Peter Zijlstra Committed by Steven Rostedt
Browse files

ring-buffer: pass in lockdep class key for reader_lock

On Sun, 7 Jun 2009, Ingo Molnar wrote:
> Testing tracer sched_switch: <6>Starting ring buffer hammer
> Testing tracer sysprof: PASSED
> Testing tracer function: PASSED
> Testing tracer irqsoff:
> =============================================
> Testing tracer preemptoff: PASSED
> Testing tracer preemptirqsoff: [ INFO: possible recursive locking detected ]
> Testing tracer branch: 2.6.30-rc8-tip-01972-ge5b9078-dirty #5760
> ---------------------------------------------
> rb_consumer/431 is trying to acquire lock:
>  (&cpu_buffer->reader_lock){......}, at: [<c109eef7>] ring_buffer_reset_cpu+0x37/0x70
> but task is already holding lock:
>  (&cpu_buffer->reader_lock){......}, at: [<c10a019e>] ring_buffer_consume+0x7e/0xc0
> other info that might help us debug this:
> 1 lock held by rb_consumer/431:
>  #0:  (&cpu_buffer->reader_lock){......}, at: [<c10a019e>] ring_buffer_consume+0x7e/0xc0

The ring buffer is a generic structure, and can be used outside of
ftrace. If ftrace traces within the use of the ring buffer, it can produce
false positives with lockdep.

This patch passes in a static lock key into the allocation of the ring
buffer, so that different ring buffers will have their own lock class.
Reported-by: default avatarIngo Molnar <>
Signed-off-by: default avatarPeter Zijlstra <>
LKML-Reference: <1244477919.13761.9042.camel@twins>

[ store key in ring buffer descriptor ]
Signed-off-by: default avatarSteven Rostedt <>
parent 918143e8
......@@ -105,7 +105,19 @@ void ring_buffer_discard_commit(struct ring_buffer *buffer,
* size is in bytes for each per CPU buffer.
struct ring_buffer *
ring_buffer_alloc(unsigned long size, unsigned flags);
__ring_buffer_alloc(unsigned long size, unsigned flags, struct lock_class_key *key);
* Because the ring buffer is generic, if other users of the ring buffer get
* traced by ftrace, it can produce lockdep warnings. We need to keep each
* ring buffer's lock class separate.
#define ring_buffer_alloc(size, flags) \
({ \
static struct lock_class_key __key; \
__ring_buffer_alloc((size), (flags), &__key); \
void ring_buffer_free(struct ring_buffer *buffer);
int ring_buffer_resize(struct ring_buffer *buffer, unsigned long size);
......@@ -426,6 +426,8 @@ struct ring_buffer {
atomic_t record_disabled;
cpumask_var_t cpumask;
struct lock_class_key *reader_lock_key;
struct mutex mutex;
struct ring_buffer_per_cpu **buffers;
......@@ -565,6 +567,7 @@ rb_allocate_cpu_buffer(struct ring_buffer *buffer, int cpu)
cpu_buffer->cpu = cpu;
cpu_buffer->buffer = buffer;
lockdep_set_class(&cpu_buffer->reader_lock, buffer->reader_lock_key);
cpu_buffer->lock = (raw_spinlock_t)__RAW_SPIN_LOCK_UNLOCKED;
......@@ -635,7 +638,8 @@ static int rb_cpu_notify(struct notifier_block *self,
* when the buffer wraps. If this flag is not set, the buffer will
* drop data when the tail hits the head.
struct ring_buffer *ring_buffer_alloc(unsigned long size, unsigned flags)
struct ring_buffer *__ring_buffer_alloc(unsigned long size, unsigned flags,
struct lock_class_key *key)
struct ring_buffer *buffer;
int bsize;
......@@ -658,6 +662,7 @@ struct ring_buffer *ring_buffer_alloc(unsigned long size, unsigned flags)
buffer->pages = DIV_ROUND_UP(size, BUF_PAGE_SIZE);
buffer->flags = flags;
buffer->clock = trace_clock_local;
buffer->reader_lock_key = key;
/* need at least two pages */
if (buffer->pages == 1)
......@@ -715,7 +720,7 @@ struct ring_buffer *ring_buffer_alloc(unsigned long size, unsigned flags)
return NULL;
* ring_buffer_free - free a ring buffer.
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