Commit-ID: cee34d88cabd1ba5fc93e09b5b12232bc9338c7c Gitweb: http://git.kernel.org/tip/cee34d88cabd1ba5fc93e09b5b12232bc9338c7c Author: Peter Zijlstra <pet...@infradead.org> AuthorDate: Tue, 2 Jun 2015 12:50:13 +0200 Committer: Ingo Molnar <mi...@kernel.org> CommitDate: Sun, 7 Jun 2015 15:46:30 +0200
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key are no longer valid.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: Jerome Marchand <jmarc...@redhat.com> Tested-by: Jerome Marchand <jmarc...@redhat.com> Signed-off-by: Peter Zijlstra (Intel) <pet...@infradead.org> Cc: Andrew Morton <a...@linux-foundation.org> Cc: H. Peter Anvin <h...@zytor.com> Cc: Linus Torvalds <torva...@linux-foundation.org> Cc: Peter Zijlstra <pet...@infradead.org> Cc: Thomas Gleixner <t...@linutronix.de> Link: http://lkml.kernel.org/r/20150602105013.gs3...@twins.programming.kicks-ass.net Signed-off-by: Ingo Molnar <mi...@kernel.org> --- kernel/locking/lockdep.c | 3 ++- kernel/locking/lockdep_proc.c | 22 +++++++++++++++++----- 2 files changed, 19 insertions(+), 6 deletions(-) diff --git a/kernel/locking/lockdep.c b/kernel/locking/lockdep.c index a0831e1..aaeae88 100644 --- a/kernel/locking/lockdep.c +++ b/kernel/locking/lockdep.c @@ -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) diff --git a/kernel/locking/lockdep_proc.c b/kernel/locking/lockdep_proc.c index ef43ac4..d83d798 100644 --- a/kernel/locking/lockdep_proc.c +++ b/kernel/locking/lockdep_proc.c @@ -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); -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
