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Commit cee34d88 authored by Peter Zijlstra's avatar Peter Zijlstra Committed by Ingo Molnar
Browse files

lockdep: Fix a race between /proc/lock_stat and module unload 



The lock_class iteration of /proc/lock_stat is not serialized against
the lockdep_free_key_range() call from module unload.

Therefore it can happen that we find a class of which ->name/->key are
no longer valid.

There is a further bug in zap_class() that left ->name dangling. Cure
this. Use RCU_INIT_POINTER() because NULL.

Since lockdep_free_key_range() is rcu_sched serialized, we can read
both ->name and ->key under rcu_read_lock_sched() (preempt-disable)
and be assured that if we observe a !NULL value it stays safe to use
for as long as we hold that lock.

If we observe both NULL, skip the entry.

Reported-by: default avatarJerome Marchand <jmarchan@redhat.com>
Tested-by: default avatarJerome Marchand <jmarchan@redhat.com>
Signed-off-by: default avatarPeter Zijlstra (Intel) <peterz@infradead.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/20150602105013.GS3644@twins.programming.kicks-ass.net


Signed-off-by: default avatarIngo Molnar <mingo@kernel.org>
parent 37ef1647

kernel/locking/lockdep.c

+2 −1
Original line number Diff line number Diff line
@@ -3900,7 +3900,8 @@ static void zap_class(struct lock_class *class) 
	list_del_rcu(&class->hash_entry);

	list_del_rcu(&class->lock_entry);



	class->key = NULL;

	RCU_INIT_POINTER(class->key, NULL);

	RCU_INIT_POINTER(class->name, NULL);

}



static inline int within(const void *addr, void *start, unsigned long size)

kernel/locking/lockdep_proc.c

+17 −5
Original line number Diff line number Diff line
@@ -426,10 +426,12 @@ static void seq_lock_time(struct seq_file *m, struct lock_time *lt) 


static void seq_stats(struct seq_file *m, struct lock_stat_data *data)

{

	char name[39];

	struct lock_class *class;

	struct lockdep_subclass_key *ckey;

	struct lock_class_stats *stats;

	struct lock_class *class;

	const char *cname;

	int i, namelen;

	char name[39];



	class = data->class;

	stats = &data->stats;
@@ -440,15 +442,25 @@ static void seq_stats(struct seq_file *m, struct lock_stat_data *data) 
	if (class->subclass)

		namelen -= 2;



	if (!class->name) {

	rcu_read_lock_sched();

	cname = rcu_dereference_sched(class->name);

	ckey  = rcu_dereference_sched(class->key);



	if (!cname && !ckey) {

		rcu_read_unlock_sched();

		return;



	} else if (!cname) {

		char str[KSYM_NAME_LEN];

		const char *key_name;



		key_name = __get_key_name(class->key, str);

		key_name = __get_key_name(ckey, str);

		snprintf(name, namelen, "%s", key_name);

	} else {

		snprintf(name, namelen, "%s", class->name);

		snprintf(name, namelen, "%s", cname);

	}

	rcu_read_unlock_sched();



	namelen = strlen(name);

	if (class->name_version > 1) {

		snprintf(name+namelen, 3, "#%d", class->name_version);