linux-kernel - [tip:locking/core] locking/lockdep: Fix the rollback and overwrite detection logic in crossrelease

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Message-ID: <tip-907dc16d7e23ec81a126c9585435494fa1b3a4b7@git.kernel.org>
Date:   Mon, 14 Aug 2017 04:46:06 -0700
From:   tip-bot for Byungchul Park <tipbot@...or.com>
To:     linux-tip-commits@...r.kernel.org
Cc:     hpa@...or.com, byungchul.park@....com, peterz@...radead.org,
        boqun.feng@...il.com, torvalds@...ux-foundation.org,
        mingo@...nel.org, tglx@...utronix.de, linux-kernel@...r.kernel.org
Subject: [tip:locking/core] locking/lockdep: Fix the rollback and overwrite
 detection logic in crossrelease

Commit-ID:  907dc16d7e23ec81a126c9585435494fa1b3a4b7
Gitweb:     http://git.kernel.org/tip/907dc16d7e23ec81a126c9585435494fa1b3a4b7
Author:     Byungchul Park <byungchul.park@....com>
AuthorDate: Mon, 14 Aug 2017 16:00:52 +0900
Committer:  Ingo Molnar <mingo@...nel.org>
CommitDate: Mon, 14 Aug 2017 12:52:17 +0200

locking/lockdep: Fix the rollback and overwrite detection logic in crossrelease

As Boqun Feng pointed out, current->hist_id should be aligned with the
latest valid xhlock->hist_id so that hist_id_save[] storing current->hist_id
can be comparable with xhlock->hist_id. Fix it.

Additionally, the condition for overwrite-detection should be the
opposite. Fix the code and the comments as well.

           <- direction to visit
hhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhh (h: history)
                 ^^        ^
                 ||        start from here
                 |previous entry
                 current entry

Reported-by: Boqun Feng <boqun.feng@...il.com>
Signed-off-by: Byungchul Park <byungchul.park@....com>
Cc: Linus Torvalds <torvalds@...ux-foundation.org>
Cc: Peter Zijlstra <peterz@...radead.org>
Cc: Thomas Gleixner <tglx@...utronix.de>
Cc: akpm@...ux-foundation.org
Cc: kernel-team@....com
Cc: kirill@...temov.name
Cc: linux-mm@...ck.org
Cc: npiggin@...il.com
Cc: walken@...gle.com
Cc: willy@...radead.org
Link: http://lkml.kernel.org/r/1502694052-16085-3-git-send-email-byungchul.park@lge.com
[ Improve the comments some more. ]
Signed-off-by: Ingo Molnar <mingo@...nel.org>
---
 kernel/locking/lockdep.c | 12 ++++++------
 1 file changed, 6 insertions(+), 6 deletions(-)

diff --git a/kernel/locking/lockdep.c b/kernel/locking/lockdep.c
index 257931e..66011c9 100644
--- a/kernel/locking/lockdep.c
+++ b/kernel/locking/lockdep.c
@@ -4853,7 +4853,7 @@ static void add_xhlock(struct held_lock *hlock)
 
 	/* Initialize hist_lock's members */
 	xhlock->hlock = *hlock;
-	xhlock->hist_id = current->hist_id++;
+	xhlock->hist_id = ++current->hist_id;
 
 	xhlock->trace.nr_entries = 0;
 	xhlock->trace.max_entries = MAX_XHLOCK_TRACE_ENTRIES;
@@ -5029,12 +5029,12 @@ static void commit_xhlocks(struct cross_lock *xlock)
 				break;
 
 			/*
-			 * Filter out the cases that the ring buffer was
-			 * overwritten and the previous entry has a bigger
-			 * hist_id than the following one, which is impossible
-			 * otherwise.
+			 * Filter out the cases where the ring buffer was
+			 * overwritten and the current entry has a bigger
+			 * hist_id than the previous one, which is impossible
+			 * otherwise:
 			 */
-			if (unlikely(before(xhlock->hist_id, prev_hist_id)))
+			if (unlikely(before(prev_hist_id, xhlock->hist_id)))
 				break;
 
 			prev_hist_id = xhlock->hist_id;