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From: Masami Hiramatsu <mhiramat@kernel.org>
To: Ingo Molnar <mingo@kernel.org>
Cc: Anders Roxell <anders.roxell@linaro.org>,
	paulmck@kernel.org, joel@joelfernandes.org,
	"Naveen N . Rao" <naveen.n.rao@linux.ibm.com>,
	Anil S Keshavamurthy <anil.s.keshavamurthy@intel.com>,
	David Miller <davem@davemloft.net>,
	Masami Hiramatsu <mhiramat@kernel.org>,
	Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
Subject: [PATCH -tip V2 1/2] kprobes: Suppress the suspicious RCU warning on kprobes
Date: Tue,  3 Dec 2019 15:06:17 +0900	[thread overview]
Message-ID: <157535317763.16485.12112495601308191775.stgit@devnote2> (raw)
In-Reply-To: <157535316659.16485.11817291759382261088.stgit@devnote2>

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.

Reported-by: Anders Roxell <anders.roxell@linaro.org>
Suggested-by: Joel Fernandes <joel@joelfernandes.org>
Signed-off-by: Masami Hiramatsu <mhiramat@kernel.org>
Reviewed-by: Joel Fernandes (Google) <joel@joelfernandes.org>
---
 kernel/kprobes.c |    3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/kernel/kprobes.c b/kernel/kprobes.c
index 53534aa258a6..f9ecb6d532fb 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;
 	}


  reply	other threads:[~2019-12-03  6:06 UTC|newest]

Thread overview: 14+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-12-03  6:06 [PATCH -tip V2 0/2] kprobes: Fix RCU warning and cleanup Masami Hiramatsu
2019-12-03  6:06 ` Masami Hiramatsu [this message]
2019-12-03  6:06 ` [PATCH -tip V2 2/2] kprobes: Use non RCU traversal APIs on kprobe_tables if possible Masami Hiramatsu
2020-01-14 13:56   ` Joel Fernandes
2020-01-15  1:31     ` Masami Hiramatsu
2019-12-20 18:55 ` [PATCH -tip V2 0/2] kprobes: Fix RCU warning and cleanup Masami Hiramatsu
2020-01-07 12:15   ` Masami Hiramatsu
2020-01-10 21:14     ` Joel Fernandes
2020-01-10 23:35       ` Masami Hiramatsu
2020-01-12  2:05         ` Joel Fernandes
2020-01-13  3:16           ` Masami Hiramatsu
2020-01-13 13:09             ` Masami Hiramatsu
2020-01-13 19:23               ` Paul E. McKenney
2020-01-14 11:49                 ` Masami Hiramatsu

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