linux-kernel - [PATCH 1/2] lockdep: Add a comment about crossrelease_hist_end() in lockdep_sys

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Date:   Mon, 14 Aug 2017 16:00:51 +0900
From:   Byungchul Park <byungchul.park@....com>
To:     peterz@...radead.org, mingo@...nel.org
Cc:     tglx@...utronix.de, walken@...gle.com, boqun.feng@...il.com,
        kirill@...temov.name, linux-kernel@...r.kernel.org,
        linux-mm@...ck.org, akpm@...ux-foundation.org, willy@...radead.org,
        npiggin@...il.com, kernel-team@....com
Subject: [PATCH 1/2] lockdep: Add a comment about crossrelease_hist_end() in lockdep_sys_exit()

In lockdep_sys_exit(), crossrelease_hist_end() is called unconditionally
even when getting here without having started e.g. just after forked.
But it's no problem since it anyway would rollback to an invalid element.
A comment would be helpful to understand this situation.

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

diff --git a/kernel/locking/lockdep.c b/kernel/locking/lockdep.c
index 1114dc4..1ae4258 100644
--- a/kernel/locking/lockdep.c
+++ b/kernel/locking/lockdep.c
@@ -4623,6 +4623,10 @@ asmlinkage __visible void lockdep_sys_exit(void)
 	/*
 	 * The lock history for each syscall should be independent. So wipe the
 	 * slate clean on return to userspace.
+	 *
+	 * crossrelease_hist_end() would work well even when getting here
+	 * without starting just after forked, it rollbacks back the index
+	 * to point to the last which is already invalid.
 	 */
 	crossrelease_hist_end(XHLOCK_PROC);
 	crossrelease_hist_start(XHLOCK_PROC);
-- 
1.9.1