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[PATCH 2/2] lockdep: Fix the rollback and overwrite detection in crossrelease

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As Boqun 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 it with modifying comment.

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Signed-off-by: Byungchul Park <byungchul.park@lge.com>
---
 kernel/locking/lockdep.c | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/kernel/locking/lockdep.c b/kernel/locking/lockdep.c
index 1ae4258..f0e6649 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;
@@ -5030,11 +5030,11 @@ static void commit_xhlocks(struct cross_lock *xlock)
 
 			/*
 			 * 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
+			 * 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;
-- 
1.9.1

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[PATCH 0/2] Fix a bug in crossrelease Byungchul Park <byungchul.park@lge.com> - 2017-08-14 09:10 +0200
  [PATCH 1/2] lockdep: Add a comment about crossrelease_hist_end() in lockdep_sys_exit() Byungchul Park <byungchul.park@lge.com> - 2017-08-14 09:10 +0200
    [tip:locking/core] locking/lockdep: Add a comment about  crossrelease_hist_end() in lockdep_sys_exit() tip-bot for Byungchul Park <tipbot@zytor.com> - 2017-08-14 13:50 +0200
  [PATCH 2/2] lockdep: Fix the rollback and overwrite detection in crossrelease Byungchul Park <byungchul.park@lge.com> - 2017-08-14 09:10 +0200
    [tip:locking/core] locking/lockdep: Fix the rollback and overwrite  detection logic in crossrelease tip-bot for Byungchul Park <tipbot@zytor.com> - 2017-08-14 14:00 +0200

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