linux-kernel - [PATCH 2/4] locking/lockdep: Remove the unnecessary trace saving

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Date:   Sat, 19 Jun 2021 01:01:08 +0800
From:   Boqun Feng <boqun.feng@...il.com>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     Ingo Molnar <mingo@...hat.com>, Will Deacon <will@...nel.org>,
        Waiman Long <longman@...hat.com>,
        Boqun Feng <boqun.feng@...il.com>,
        linux-kernel@...r.kernel.org,
        Johannes Berg <johannes@...solutions.net>
Subject: [PATCH 2/4] locking/lockdep: Remove the unnecessary trace saving

In print_bad_irq_dependency(), save_trace() is called to set the ->trace
for @prev_root as the current call trace, however @prev_root corresponds
to the the held lock, which may not be acquired in current call trace,
therefore it's wrong to use save_trace() to set ->trace of @prev_root.
Moreover, with our adjustment of printing backwards dependency path, the
->trace of @prev_root is unncessary, so remove it.

Reported-by: Johannes Berg <johannes@...solutions.net>
Signed-off-by: Boqun Feng <boqun.feng@...il.com>
---
 kernel/locking/lockdep.c | 3 ---
 1 file changed, 3 deletions(-)

diff --git a/kernel/locking/lockdep.c b/kernel/locking/lockdep.c
index 3b32cd9cdfd0..74d084a398be 100644
--- a/kernel/locking/lockdep.c
+++ b/kernel/locking/lockdep.c
@@ -2550,9 +2550,6 @@ print_bad_irq_dependency(struct task_struct *curr,
 	lockdep_print_held_locks(curr);
 
 	pr_warn("\nthe dependencies between %s-irq-safe lock and the holding lock:\n", irqclass);
-	prev_root->trace = save_trace();
-	if (!prev_root->trace)
-		return;
 	print_shortest_lock_dependencies_backwards(backwards_entry, prev_root);
 
 	pr_warn("\nthe dependencies between the lock to be acquired");
-- 
2.30.2