From: Byungchul Park <byungchul.park@lge.com>
To: peterz@infradead.org, mingo@kernel.org
Cc: tglx@linutronix.de, linux-kernel@vger.kernel.org,
linux-mm@kvack.org, linux-block@vger.kernel.org,
kernel-team@lge.com
Subject: [PATCH v3 4/5] locking/Documentation: Add an example to help crossrelease.txt more readable
Date: Sat, 11 Nov 2017 22:26:31 +0900 [thread overview]
Message-ID: <1510406792-28676-5-git-send-email-byungchul.park@lge.com> (raw)
In-Reply-To: <1510406792-28676-1-git-send-email-byungchul.park@lge.com>
Add an example explaining the rationale that the limitation that old
lockdep implies, can be relaxed.
Signed-off-by: Byungchul Park <byungchul.park@lge.com>
---
Documentation/locking/crossrelease.txt | 23 +++++++++++++++++++++++
1 file changed, 23 insertions(+)
diff --git a/Documentation/locking/crossrelease.txt b/Documentation/locking/crossrelease.txt
index bb449e8..dac56f4 100644
--- a/Documentation/locking/crossrelease.txt
+++ b/Documentation/locking/crossrelease.txt
@@ -281,6 +281,29 @@ causes a deadlock. The more lockdep adds dependencies, the more it
thoroughly works. Thus, lockdep has to do its best to detect and add as
many true dependencies to the graph as possible.
+For example:
+
+ CONTEXT X CONTEXT Y
+ --------- ---------
+ acquire A
+ acquire B /* A dependency 'A -> B' exists */
+ release B
+ release A held by Y
+
+ where A and B are different lock classes.
+
+In this case, a dependency 'A -> B' exists since:
+
+ 1. A waiter for A and a waiter for B might exist when acquiring B.
+ 2. The only way to wake up each is to release what it waits for.
+ 3. Whether the waiter for A can be woken up depends on whether the
+ other can. In other words, CONTEXT X cannot release A if it fails
+ to acquire B.
+
+Considering only typical locks, lockdep builds nothing. However,
+relaxing the limitation, a dependency 'A -> B' can be added, giving us
+more chances to check circular dependencies.
+
However, it might suffer performance degradation since
relaxing the limitation, with which design and implementation of lockdep
can be efficient, might introduce inefficiency inevitably. So lockdep
--
1.9.1
next prev parent reply other threads:[~2017-11-11 13:28 UTC|newest]
Thread overview: 12+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-11-11 13:26 [PATCH v3 0/5] Revise crossrelease.txt Byungchul Park
2017-11-11 13:26 ` [PATCH v3 1/5] locking/Documentation: Remove meaningless examples and a note Byungchul Park
2017-11-11 13:26 ` [PATCH v3 2/5] locking/Documentation: Fix typos and clear grammar errors Byungchul Park
2017-11-11 13:26 ` [PATCH v3 3/5] locking/Documentation: Fix weird expressions Byungchul Park
2017-11-11 13:26 ` Byungchul Park [this message]
2017-11-11 13:26 ` [PATCH v3 5/5] locking/Documentation: Align crossrelease.txt with the width Byungchul Park
2017-11-11 13:33 ` [PATCH] locking/Documentation: Revise Documentation/locking/crossrelease.txt Byungchul Park
2017-11-11 13:45 ` Byungchul Park
2017-11-16 0:04 ` Byungchul Park
2017-11-16 7:22 ` Ingo Molnar
2017-11-16 7:36 ` Byungchul Park
2017-12-04 0:15 ` Byungchul Park
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