linux-kernel - [tip: locking/core] lockdep: Add recursive read locks into dependency graph

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Date:   Thu, 27 Aug 2020 07:54:17 -0000
From:   "tip-bot2 for Boqun Feng" <tip-bot2@...utronix.de>
To:     linux-tip-commits@...r.kernel.org
Cc:     Boqun Feng <boqun.feng@...il.com>,
        "Peter Zijlstra (Intel)" <peterz@...radead.org>,
        x86 <x86@...nel.org>, LKML <linux-kernel@...r.kernel.org>
Subject: [tip: locking/core] lockdep: Add recursive read locks into dependency graph

The following commit has been merged into the locking/core branch of tip:

Commit-ID:     621c9dac0eea7607cb9a57cc9ba47fbcd4e644c9
Gitweb:        https://git.kernel.org/tip/621c9dac0eea7607cb9a57cc9ba47fbcd4e644c9
Author:        Boqun Feng <boqun.feng@...il.com>
AuthorDate:    Fri, 07 Aug 2020 15:42:31 +08:00
Committer:     Peter Zijlstra <peterz@...radead.org>
CommitterDate: Wed, 26 Aug 2020 12:42:06 +02:00

lockdep: Add recursive read locks into dependency graph

Since we have all the fundamental to handle recursive read locks, we now
add them into the dependency graph.

Signed-off-by: Boqun Feng <boqun.feng@...il.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
Link: https://lkml.kernel.org/r/20200807074238.1632519-13-boqun.feng@gmail.com
---
 kernel/locking/lockdep.c | 19 ++-----------------
 1 file changed, 2 insertions(+), 17 deletions(-)

diff --git a/kernel/locking/lockdep.c b/kernel/locking/lockdep.c
index 6644974..b87766e 100644
--- a/kernel/locking/lockdep.c
+++ b/kernel/locking/lockdep.c
@@ -2809,16 +2809,6 @@ check_prev_add(struct task_struct *curr, struct held_lock *prev,
 		return 0;
 
 	/*
-	 * For recursive read-locks we do all the dependency checks,
-	 * but we dont store read-triggered dependencies (only
-	 * write-triggered dependencies). This ensures that only the
-	 * write-side dependencies matter, and that if for example a
-	 * write-lock never takes any other locks, then the reads are
-	 * equivalent to a NOP.
-	 */
-	if (next->read == 2 || prev->read == 2)
-		return 1;
-	/*
 	 * Is the <prev> -> <next> dependency already present?
 	 *
 	 * (this may occur even though this is a new chain: consider
@@ -2935,13 +2925,8 @@ check_prevs_add(struct task_struct *curr, struct held_lock *next)
 		u16 distance = curr->lockdep_depth - depth + 1;
 		hlock = curr->held_locks + depth - 1;
 
-		/*
-		 * Only non-recursive-read entries get new dependencies
-		 * added:
-		 */
-		if (hlock->read != 2 && hlock->check) {
-			int ret = check_prev_add(curr, hlock, next, distance,
-						 &trace);
+		if (hlock->check) {
+			int ret = check_prev_add(curr, hlock, next, distance, &trace);
 			if (!ret)
 				return 0;