From: Byungchul Park <byungchul.park@lge.com>
To: linux-kernel@vger.kernel.org
Cc: kernel-team@lge.com, ying.huang@intel.com, peterz@infradead.org,
mingo@kernel.org, jiangshanlai@gmail.com,
paulmck@linux.vnet.ibm.com, josh@joshtriplett.org,
rostedt@goodmis.org, mathieu.desnoyers@efficios.com,
joel@joelfernandes.org, len.brown@intel.com, glider@google.com,
peter@hurleysoftware.com, aik@ozlabs.ru
Subject: [QUESTION] llist: Comment releasing 'must delete' restriction before traversing
Date: Tue, 31 Jul 2018 09:58:36 +0900 [thread overview]
Message-ID: <1532998716-5037-1-git-send-email-byungchul.park@lge.com> (raw)
Hello folks,
I'm careful in saying.. and curious about..
In restrictive cases like only addtions happen but never deletion, can't
we safely traverse a llist? I believe llist can be more useful if we can
release the restriction. Can't we?
If yes, we may add another function traversing starting from a head. Or
just use existing funtion with head->first.
Thank a lot for your answers in advance :)
----->8-----
From 1e73882799b269cd86e7a7c955021e3a18d1e6cf Mon Sep 17 00:00:00 2001
From: Byungchul Park <byungchul.park@lge.com>
Date: Tue, 31 Jul 2018 09:31:57 +0900
Subject: [QUESTION] llist: Comment releasing 'must delete' restriction before
traversing
llist traversing can run without deletion in restrictive cases all
items are added but never deleted like a rculist traversing such as
list_for_each_entry_lockless. So add the comment.
Signed-off-by: Byungchul Park <byungchul.park@lge.com>
---
include/linux/llist.h | 24 ++++++++++++++++++------
1 file changed, 18 insertions(+), 6 deletions(-)
diff --git a/include/linux/llist.h b/include/linux/llist.h
index 85abc29..d012d3e 100644
--- a/include/linux/llist.h
+++ b/include/linux/llist.h
@@ -32,8 +32,12 @@
* operation, with "-" being no lock needed, while "L" being lock is needed.
*
* The list entries deleted via llist_del_all can be traversed with
- * traversing function such as llist_for_each etc. But the list
- * entries can not be traversed safely before deleted from the list.
+ * traversing function such as llist_for_each etc. Normally the list
+ * entries cannot be traversed safely before deleted from the list
+ * except the cases items are added to the list but never deleted. In
+ * that restrictive cases the list may be safely traversed concurrently
+ * with llist_add.
+ *
* The order of deleted entries is from the newest to the oldest added
* one. If you want to traverse from the oldest to the newest, you
* must reverse the order by yourself before traversing.
@@ -116,7 +120,9 @@ static inline void init_llist_head(struct llist_head *list)
*
* In general, some entries of the lock-less list can be traversed
* safely only after being deleted from list, so start with an entry
- * instead of list head.
+ * instead of list head. But in restrictive cases items are added to
+ * the list but never deleted, the list may be safely traversed
+ * concurrently with llist_add.
*
* If being used on entries deleted from lock-less list directly, the
* traverse order is from the newest to the oldest added entry. If
@@ -135,7 +141,9 @@ static inline void init_llist_head(struct llist_head *list)
*
* In general, some entries of the lock-less list can be traversed
* safely only after being deleted from list, so start with an entry
- * instead of list head.
+ * instead of list head. But in restrictive cases items are added to
+ * the list but never deleted, the list may be safely traversed
+ * concurrently with llist_add.
*
* If being used on entries deleted from lock-less list directly, the
* traverse order is from the newest to the oldest added entry. If
@@ -153,7 +161,9 @@ static inline void init_llist_head(struct llist_head *list)
*
* In general, some entries of the lock-less list can be traversed
* safely only after being removed from list, so start with an entry
- * instead of list head.
+ * instead of list head. But in restrictive cases items are added to
+ * the list but never deleted, the list may be safely traversed
+ * concurrently with llist_add.
*
* If being used on entries deleted from lock-less list directly, the
* traverse order is from the newest to the oldest added entry. If
@@ -175,7 +185,9 @@ static inline void init_llist_head(struct llist_head *list)
*
* In general, some entries of the lock-less list can be traversed
* safely only after being removed from list, so start with an entry
- * instead of list head.
+ * instead of list head. But in restrictive cases items are added to
+ * the list but never deleted, the list may be safely traversed
+ * concurrently with llist_add.
*
* If being used on entries deleted from lock-less list directly, the
* traverse order is from the newest to the oldest added entry. If
--
1.9.1
next reply other threads:[~2018-07-31 0:58 UTC|newest]
Thread overview: 14+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-07-31 0:58 Byungchul Park [this message]
2018-07-31 1:37 ` [QUESTION] llist: Comment releasing 'must delete' restriction before traversing Huang, Ying
2018-07-31 5:25 ` Byungchul Park
2018-07-31 5:45 ` Huang, Ying
2018-07-31 4:30 ` Paul E. McKenney
2018-07-31 9:29 ` Byungchul Park
2018-07-31 14:30 ` Paul E. McKenney
2018-08-01 5:34 ` Byungchul Park
2018-08-01 5:43 ` Huang, Ying
2018-08-01 8:52 ` Byungchul Park
2018-07-31 8:52 ` Peter Zijlstra
2018-07-31 9:38 ` Byungchul Park
2018-07-31 13:46 ` Steven Rostedt
2018-08-01 5:35 ` Byungchul Park
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