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| author | Peter Zijlstra <peterz@infradead.org> | 2015-06-02 12:50:13 +0200 |
|---|---|---|
| committer | Ingo Molnar <mingo@kernel.org> | 2015-06-07 15:46:30 +0200 |
| commit | cee34d88cabd1ba5fc93e09b5b12232bc9338c7c (patch) | |
| tree | 278d17b06e20285f8c2822d724ecc41a69b27e9d /kernel/locking | |
| parent | 37ef1647b7f73d4ff4c7993984599b6c4f26443a (diff) | |
| download | linux-cee34d88cabd1ba5fc93e09b5b12232bc9338c7c.tar.gz linux-cee34d88cabd1ba5fc93e09b5b12232bc9338c7c.tar.bz2 linux-cee34d88cabd1ba5fc93e09b5b12232bc9338c7c.zip | |
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no longer valid.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 <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>
Diffstat (limited to 'kernel/locking')
| -rw-r--r-- | kernel/locking/lockdep.c | 3 | ||||
| -rw-r--r-- | 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 a0831e1b99f4..aaeae885d9af 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 ef43ac4bafb5..d83d798bef95 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); |