[tip: locking/core] locking/lockdep: Remove the unnecessary trace saving

[tip-bot2 for Boqun Feng]

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

Commit-ID:     d4c157c7b1a67a0844a904baaca9a840c196c103
Gitweb:        https://git.kernel.org/tip/d4c157c7b1a67a0844a904baaca9a840c196c103
Author:        Boqun Feng <boqun.feng@xxxxxxxxx>
AuthorDate:    Sat, 19 Jun 2021 01:01:08 +08:00
Committer:     Peter Zijlstra <peterz@xxxxxxxxxxxxx>
CommitterDate: Tue, 22 Jun 2021 16:42:07 +02:00

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@xxxxxxxxxxxxxxxx>
Signed-off-by: Boqun Feng <boqun.feng@xxxxxxxxx>
Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
Link: https://lore.kernel.org/r/20210618170110.3699115-3-boqun.feng@xxxxxxxxx
---
 kernel/locking/lockdep.c | 3 ---
 1 file changed, 3 deletions(-)

diff --git a/kernel/locking/lockdep.c b/kernel/locking/lockdep.c
index 3b32cd9..74d084a 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");