lockdep: Fix a race between /proc/lock_stat and module unload (cee34d88) · Commits · 戴 / test

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key are no longer valid.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:

Jerome Marchand <jmarchan@redhat.com> Tested-by:

Jerome Marchand <jmarchan@redhat.com> Signed-off-by:

Peter 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:

Ingo Molnar <mingo@kernel.org>

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);

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