linux-kernel - [PATCH] lockdep: Let lock_is_held_type() detect recursive read as read

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Message-ID: <20210901162255.u2vhecaxgjsjfdtc@linutronix.de>
Date:   Wed, 1 Sep 2021 18:22:55 +0200
From:   Sebastian Andrzej Siewior <bigeasy@...utronix.de>
To:     linux-kernel@...r.kernel.org
Cc:     Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>, Will Deacon <will@...nel.org>,
        Waiman Long <longman@...hat.com>,
        Boqun Feng <boqun.feng@...il.com>,
        Thomas Gleixner <tglx@...utronix.de>
Subject: [PATCH] lockdep: Let lock_is_held_type() detect recursive read as
 read

lock_is_held_type(, 1) detects acquired read locks. It only recognized
locks acquired with lock_acquire_shared(). Read locks acquired with
lock_acquire_shared_recursive() are not recognized because a `2' is
stored as the read value.

Rework the check to additionally recognise lock's read value one and two
as a read held lock.

Fixes: e918188611f07 ("locking: More accurate annotations for read_lock()")
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@...utronix.de>
---

On a related note: What exactly means read_lock_is_recursive() in terms
of recursive locking? The second items mentions QRW locks. Does this
mean that a pending WRITER blocks further READER from acquiring the
lock?

 kernel/locking/lockdep.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/kernel/locking/lockdep.c b/kernel/locking/lockdep.c
index f15df3fd7c5a6..39f98454a8827 100644
--- a/kernel/locking/lockdep.c
+++ b/kernel/locking/lockdep.c
@@ -5366,7 +5366,9 @@ int __lock_is_held(const struct lockdep_map *lock, int read)
 		struct held_lock *hlock = curr->held_locks + i;
 
 		if (match_held_lock(hlock, lock)) {
-			if (read == -1 || hlock->read == read)
+			if (read == -1 ||
+			    (read == 0 && hlock->read == 0) ||
+			    (read == 1 && hlock->read > 0))
 				return LOCK_STATE_HELD;
 
 			return LOCK_STATE_NOT_HELD;
-- 
2.33.0