From: Masami Hiramatsu <mhiramat@xxxxxxxxxx> [ Upstream commit 6743ad432ec92e680cd0d9db86cb17b949cf5a43 ] Anders reported that the lockdep warns that suspicious RCU list usage in register_kprobe() (detected by CONFIG_PROVE_RCU_LIST.) This is because get_kprobe() access kprobe_table[] by hlist_for_each_entry_rcu() without rcu_read_lock. If we call get_kprobe() from the breakpoint handler context, it is run with preempt disabled, so this is not a problem. But in other cases, instead of rcu_read_lock(), we locks kprobe_mutex so that the kprobe_table[] is not updated. So, current code is safe, but still not good from the view point of RCU. Joel suggested that we can silent that warning by passing lockdep_is_held() to the last argument of hlist_for_each_entry_rcu(). Add lockdep_is_held(&kprobe_mutex) at the end of the hlist_for_each_entry_rcu() to suppress the warning. Link: http://lkml.kernel.org/r/158927055350.27680.10261450713467997503.stgit@devnote2 Reported-by: Anders Roxell <anders.roxell@xxxxxxxxxx> Suggested-by: Joel Fernandes <joel@xxxxxxxxxxxxxxxxx> Reviewed-by: Joel Fernandes (Google) <joel@xxxxxxxxxxxxxxxxx> Signed-off-by: Masami Hiramatsu <mhiramat@xxxxxxxxxx> Signed-off-by: Steven Rostedt (VMware) <rostedt@xxxxxxxxxxx> Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx> --- kernel/kprobes.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-) diff --git a/kernel/kprobes.c b/kernel/kprobes.c index 195ecb955fcc5..950a5cfd262ce 100644 --- a/kernel/kprobes.c +++ b/kernel/kprobes.c @@ -326,7 +326,8 @@ struct kprobe *get_kprobe(void *addr) struct kprobe *p; head = &kprobe_table[hash_ptr(addr, KPROBE_HASH_BITS)]; - hlist_for_each_entry_rcu(p, head, hlist) { + hlist_for_each_entry_rcu(p, head, hlist, + lockdep_is_held(&kprobe_mutex)) { if (p->addr == addr) return p; } -- 2.25.1
