[PATCH 05/18] ftrace, kprobes: Fix a deadlock on ftrace_regex_lock

Steven Rostedt
2013-05-11T00:13:49Z

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From: Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com>

Fix a deadlock on ftrace_regex_lock which happens when setting
an enable_event trigger on dynamic kprobe event as below.

----
sh-2.05b# echo p vfs_symlink > kprobe_events
sh-2.05b# echo vfs_symlink:enable_event:kprobes:p_vfs_symlink_0 > set_ftrace_filter

=============================================
[ INFO: possible recursive locking detected ]
3.9.0+ #35 Not tainted
---------------------------------------------
sh/72 is trying to acquire lock:
(ftrace_regex_lock){+.+.+.}, at: [<ffffffff810ba6c1>] ftrace_set_hash+0x81/0x1f0

but task is already holding lock:
(ftrace_regex_lock){+.+.+.}, at: [<ffffffff810b7cbd>] ftrace_regex_write.isra.29.part.30+0x3d/0x220

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

CPU0
----
lock(ftrace_regex_lock);
lock(ftrace_regex_lock);

*** DEADLOCK ***
----

To fix that, this introduces a finer regex_lock for each ftrace_ops.
ftrace_regex_lock is too big of a lock which protects all
filter/notrace_hash operations, but it doesn't need to be a global
lock after supporting multiple ftrace_ops because each ftrace_ops
has its own filter/notrace_hash.

Link: http://lkml.kernel.org/r/20130509054417.30398.84254.stgit@mhiramat-M0-7522

Cc: Srikar Dronamraju <srikar@linux.vnet.ibm.com>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Tom Zanussi <tom.zanussi@intel.com>
Signed-off-by: Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com>
[ Added initialization flag and automate mutex initialization for
non ftrace.c ftrace_probes. ]
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
---
include/linux/ftrace.h | 4 +++
kernel/trace/ftrace.c | 73 ++++++++++++++++++++++++++++++++++--------------
2 files changed, 56 insertions(+), 21 deletions(-)

diff --git a/include/linux/ftrace.h b/include/linux/ftrace.h
index f83e17a..99d0fbc 100644
--- a/include/linux/ftrace.h
+++ b/include/linux/ftrace.h
@@ -90,6 +90,8 @@ typedef void (*ftrace_func_t)(unsigned long ip, unsigned long parent_ip,
* not set this, then the ftrace infrastructure will add recursion
* protection for the caller.
* STUB - The ftrace_ops is just a place holder.
+ * INITIALIZED - The ftrace_ops has already been initialized (first use time
+ * register_ftrace_function() is called, it will initialized the ops)
*/
enum {
FTRACE_OPS_FL_ENABLED = 1 << 0,
@@ -100,6 +102,7 @@ enum {
FTRACE_OPS_FL_SAVE_REGS_IF_SUPPORTED = 1 << 5,
FTRACE_OPS_FL_RECURSION_SAFE = 1 << 6,
FTRACE_OPS_FL_STUB = 1 << 7,
+ FTRACE_OPS_FL_INITIALIZED = 1 << 8,
};

struct ftrace_ops {
@@ -110,6 +113,7 @@ struct ftrace_ops {
#ifdef CONFIG_DYNAMIC_FTRACE
struct ftrace_hash *notrace_hash;
struct ftrace_hash *filter_hash;
+ struct mutex regex_lock;
#endif
};

diff --git a/kernel/trace/ftrace.c b/kernel/trace/ftrace.c
index d85a0ad..827f2fe 100644
--- a/kernel/trace/ftrace.c
+++ b/kernel/trace/ftrace.c
@@ -64,6 +64,13 @@

#define FL_GLOBAL_CONTROL_MASK (FTRACE_OPS_FL_GLOBAL | FTRACE_OPS_FL_CONTROL)

+#ifdef CONFIG_DYNAMIC_FTRACE
+#define INIT_REGEX_LOCK(opsname) \
+ .regex_lock = __MUTEX_INITIALIZER(opsname.regex_lock),
+#else
+#define INIT_REGEX_LOCK(opsname)
+#endif
+
static struct ftrace_ops ftrace_list_end __read_mostly = {
.func = ftrace_stub,
.flags = FTRACE_OPS_FL_RECURSION_SAFE | FTRACE_OPS_FL_STUB,
@@ -131,6 +138,16 @@ static void ftrace_ops_no_ops(unsigned long ip, unsigned long parent_ip);
while (likely(op = rcu_dereference_raw((op)->next)) && \
unlikely((op) != &ftrace_list_end))

+static inline void ftrace_ops_init(struct ftrace_ops *ops)
+{
+#ifdef CONFIG_DYNAMIC_FTRACE
+ if (!(ops->flags & FTRACE_OPS_FL_INITIALIZED)) {
+ mutex_init(&ops->regex_lock);
+ ops->flags |= FTRACE_OPS_FL_INITIALIZED;
+ }
+#endif
+}
+
/**
* ftrace_nr_registered_ops - return number of ops registered
*
@@ -907,7 +924,8 @@ static void unregister_ftrace_profiler(void)
#else
static struct ftrace_ops ftrace_profile_ops __read_mostly = {
.func = function_profile_call,
- .flags = FTRACE_OPS_FL_RECURSION_SAFE,
+ .flags = FTRACE_OPS_FL_RECURSION_SAFE | FTRACE_OPS_FL_INITIALIZED,
+ INIT_REGEX_LOCK(ftrace_profile_ops)
};

static int register_ftrace_profiler(void)
@@ -1103,11 +1121,10 @@ static struct ftrace_ops global_ops = {
.func = ftrace_stub,
.notrace_hash = EMPTY_HASH,
.filter_hash = EMPTY_HASH,
- .flags = FTRACE_OPS_FL_RECURSION_SAFE,
+ .flags = FTRACE_OPS_FL_RECURSION_SAFE | FTRACE_OPS_FL_INITIALIZED,
+ INIT_REGEX_LOCK(global_ops)
};

-static DEFINE_MUTEX(ftrace_regex_lock);
-
struct ftrace_page {
struct ftrace_page *next;
struct dyn_ftrace *records;
@@ -1247,6 +1264,7 @@ static void free_ftrace_hash_rcu(struct ftrace_hash *hash)

void ftrace_free_filter(struct ftrace_ops *ops)
{
+ ftrace_ops_init(ops);
free_ftrace_hash(ops->filter_hash);
free_ftrace_hash(ops->notrace_hash);
}
@@ -2624,6 +2642,8 @@ ftrace_regex_open(struct ftrace_ops *ops, int flag,
struct ftrace_hash *hash;
int ret = 0;

+ ftrace_ops_init(ops);
+
if (unlikely(ftrace_disabled))
return -ENODEV;

@@ -2656,7 +2676,7 @@ ftrace_regex_open(struct ftrace_ops *ops, int flag,
}
}

- mutex_lock(&ftrace_regex_lock);
+ mutex_lock(&ops->regex_lock);

if ((file->f_mode & FMODE_WRITE) &&
(file->f_flags & O_TRUNC))
@@ -2677,7 +2697,7 @@ ftrace_regex_open(struct ftrace_ops *ops, int flag,
}
} else
file->private_data = iter;
- mutex_unlock(&ftrace_regex_lock);
+ mutex_unlock(&ops->regex_lock);

return ret;
}
@@ -2910,6 +2930,8 @@ static void function_trace_probe_call(unsigned long ip, unsigned long parent_ip,
static struct ftrace_ops trace_probe_ops __read_mostly =
{
.func = function_trace_probe_call,
+ .flags = FTRACE_OPS_FL_INITIALIZED,
+ INIT_REGEX_LOCK(trace_probe_ops)
};

static int ftrace_probe_registered;
@@ -3256,18 +3278,18 @@ ftrace_regex_write(struct file *file, const char __user *ubuf,
if (!cnt)
return 0;

- mutex_lock(&ftrace_regex_lock);
-
- ret = -ENODEV;
- if (unlikely(ftrace_disabled))
- goto out_unlock;
-
if (file->f_mode & FMODE_READ) {
struct seq_file *m = file->private_data;
iter = m->private;
} else
iter = file->private_data;

+ mutex_lock(&iter->ops->regex_lock);
+
+ ret = -ENODEV;
+ if (unlikely(ftrace_disabled))
+ goto out_unlock;
+
parser = &iter->parser;
read = trace_get_user(parser, ubuf, cnt, ppos);

@@ -3282,7 +3304,7 @@ ftrace_regex_write(struct file *file, const char __user *ubuf,

ret = read;
out_unlock:
- mutex_unlock(&ftrace_regex_lock);
+ mutex_unlock(&iter->ops->regex_lock);

return ret;
}
@@ -3344,7 +3366,7 @@ ftrace_set_hash(struct ftrace_ops *ops, unsigned char *buf, int len,
if (!hash)
return -ENOMEM;

- mutex_lock(&ftrace_regex_lock);
+ mutex_lock(&ops->regex_lock);
if (reset)
ftrace_filter_reset(hash);
if (buf && !ftrace_match_records(hash, buf, len)) {
@@ -3366,7 +3388,7 @@ ftrace_set_hash(struct ftrace_ops *ops, unsigned char *buf, int len,
mutex_unlock(&ftrace_lock);

out_regex_unlock:
- mutex_unlock(&ftrace_regex_lock);
+ mutex_unlock(&ops->regex_lock);

free_ftrace_hash(hash);
return ret;
@@ -3392,6 +3414,7 @@ ftrace_set_addr(struct ftrace_ops *ops, unsigned long ip, int remove,
int ftrace_set_filter_ip(struct ftrace_ops *ops, unsigned long ip,
int remove, int reset)
{
+ ftrace_ops_init(ops);
return ftrace_set_addr(ops, ip, remove, reset, 1);
}
EXPORT_SYMBOL_GPL(ftrace_set_filter_ip);
@@ -3416,6 +3439,7 @@ ftrace_set_regex(struct ftrace_ops *ops, unsigned char *buf, int len,
int ftrace_set_filter(struct ftrace_ops *ops, unsigned char *buf,
int len, int reset)
{
+ ftrace_ops_init(ops);
return ftrace_set_regex(ops, buf, len, reset, 1);
}
EXPORT_SYMBOL_GPL(ftrace_set_filter);
@@ -3434,6 +3458,7 @@ EXPORT_SYMBOL_GPL(ftrace_set_filter);
int ftrace_set_notrace(struct ftrace_ops *ops, unsigned char *buf,
int len, int reset)
{
+ ftrace_ops_init(ops);
return ftrace_set_regex(ops, buf, len, reset, 0);
}
EXPORT_SYMBOL_GPL(ftrace_set_notrace);
@@ -3524,6 +3549,8 @@ ftrace_set_early_filter(struct ftrace_ops *ops, char *buf, int enable)
{
char *func;

+ ftrace_ops_init(ops);
+
while (buf) {
func = strsep(&buf, ",");
ftrace_set_regex(ops, func, strlen(func), 0, enable);
@@ -3551,14 +3578,14 @@ int ftrace_regex_release(struct inode *inode, struct file *file)
int filter_hash;
int ret;

- mutex_lock(&ftrace_regex_lock);
if (file->f_mode & FMODE_READ) {
iter = m->private;
-
seq_release(inode, file);
} else
iter = file->private_data;

+ mutex_lock(&iter->ops->regex_lock);
+
parser = &iter->parser;
if (trace_parser_loaded(parser)) {
parser->buffer[parser->idx] = 0;
@@ -3587,7 +3614,7 @@ int ftrace_regex_release(struct inode *inode, struct file *file)
free_ftrace_hash(iter->hash);
kfree(iter);

- mutex_unlock(&ftrace_regex_lock);
+ mutex_unlock(&iter->ops->regex_lock);
return 0;
}

@@ -4126,7 +4153,8 @@ void __init ftrace_init(void)

static struct ftrace_ops global_ops = {
.func = ftrace_stub,
- .flags = FTRACE_OPS_FL_RECURSION_SAFE,
+ .flags = FTRACE_OPS_FL_RECURSION_SAFE | FTRACE_OPS_FL_INITIALIZED,
+ INIT_REGEX_LOCK(global_ops)
};

static int __init ftrace_nodyn_init(void)
@@ -4180,8 +4208,9 @@ ftrace_ops_control_func(unsigned long ip, unsigned long parent_ip,
}

static struct ftrace_ops control_ops = {
- .func = ftrace_ops_control_func,
- .flags = FTRACE_OPS_FL_RECURSION_SAFE,
+ .func = ftrace_ops_control_func,
+ .flags = FTRACE_OPS_FL_RECURSION_SAFE | FTRACE_OPS_FL_INITIALIZED,
+ INIT_REGEX_LOCK(control_ops)
};

static inline void
@@ -4539,6 +4568,8 @@ int register_ftrace_function(struct ftrace_ops *ops)
{
int ret = -1;

+ ftrace_ops_init(ops);
+
mutex_lock(&ftrace_lock);

ret = __register_ftrace_function(ops);