From: Masami Hiramatsu Date: Tue, 12 May 2020 08:02:33 +0000 (+0900) Subject: kprobes: Suppress the suspicious RCU warning on kprobes X-Git-Tag: v5.4.50~44 X-Git-Url: http://review.tizen.org/git/?a=commitdiff_plain;h=d14eb5d8f0f4a2783e2125e0ba8a6732b345cc35;p=platform%2Fkernel%2Flinux-rpi.git kprobes: Suppress the suspicious RCU warning on kprobes [ 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 Suggested-by: Joel Fernandes Reviewed-by: Joel Fernandes (Google) Signed-off-by: Masami Hiramatsu Signed-off-by: Steven Rostedt (VMware) Signed-off-by: Sasha Levin --- diff --git a/kernel/kprobes.c b/kernel/kprobes.c index 195ecb9..950a5cf 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; }