From: Will Deacon <will@kernel.org>
To: linux-kernel@vger.kernel.org
Cc: Will Deacon <will@kernel.org>, Eric Dumazet <edumazet@google.com>,
Jann Horn <jannh@google.com>, Kees Cook <keescook@chromium.org>,
Maddie Stone <maddiestone@google.com>,
Marco Elver <elver@google.com>,
"Paul E . McKenney" <paulmck@kernel.org>,
Peter Zijlstra <peterz@infradead.org>,
Thomas Gleixner <tglx@linutronix.de>,
kernel-team@android.com, kernel-hardening@lists.openwall.com
Subject: [RFC PATCH 01/21] list: Remove hlist_unhashed_lockless()
Date: Tue, 24 Mar 2020 15:36:23 +0000 [thread overview]
Message-ID: <20200324153643.15527-2-will@kernel.org> (raw)
In-Reply-To: <20200324153643.15527-1-will@kernel.org>
Commit c54a2744497d ("list: Add hlist_unhashed_lockless()") added a
"lockless" variant of hlist_unhashed() that uses READ_ONCE() to access
the 'pprev' pointer of the 'hlist_node', the intention being that this
could be used by 'timer_pending()' to silence a KCSAN warning. As well
as forgetting to add the caller, the patch also sprinkles
{READ,WRITE}_ONCE() invocations over the standard (i.e. non-RCU) hlist
code, which is undesirable for a number of reasons:
1. It gives the misleading impression that the non-RCU hlist code is
in some way lock-free (despite the notable absence of any memory
barriers!) and silences KCSAN in such cases.
2. It unnecessarily penalises code generation for non-RCU hlist users
3. It makes it difficult to introduce list integrity checks because
of the possibility of concurrent callers.
Retain the {READ,WRITE}_ONCE() invocations for the RCU hlist code, but
remove them from the non-RCU implementation. Remove the unused
'hlist_unhashed_lockless()' function entirely and add the READ_ONCE()
to hlist_unhashed(), as we do already for hlist_empty() already.
Cc: Eric Dumazet <edumazet@google.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Paul E. McKenney <paulmck@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: Will Deacon <will@kernel.org>
---
include/linux/list.h | 33 ++++++++++-----------------------
1 file changed, 10 insertions(+), 23 deletions(-)
diff --git a/include/linux/list.h b/include/linux/list.h
index 884216db3246..4fed5a0f9b77 100644
--- a/include/linux/list.h
+++ b/include/linux/list.h
@@ -777,19 +777,6 @@ static inline void INIT_HLIST_NODE(struct hlist_node *h)
* node in unhashed state, but hlist_nulls_del() does not.
*/
static inline int hlist_unhashed(const struct hlist_node *h)
-{
- return !h->pprev;
-}
-
-/**
- * hlist_unhashed_lockless - Version of hlist_unhashed for lockless use
- * @h: Node to be checked
- *
- * This variant of hlist_unhashed() must be used in lockless contexts
- * to avoid potential load-tearing. The READ_ONCE() is paired with the
- * various WRITE_ONCE() in hlist helpers that are defined below.
- */
-static inline int hlist_unhashed_lockless(const struct hlist_node *h)
{
return !READ_ONCE(h->pprev);
}
@@ -852,11 +839,11 @@ static inline void hlist_del_init(struct hlist_node *n)
static inline void hlist_add_head(struct hlist_node *n, struct hlist_head *h)
{
struct hlist_node *first = h->first;
- WRITE_ONCE(n->next, first);
+ n->next = first;
if (first)
- WRITE_ONCE(first->pprev, &n->next);
+ first->pprev = &n->next;
WRITE_ONCE(h->first, n);
- WRITE_ONCE(n->pprev, &h->first);
+ n->pprev = &h->first;
}
/**
@@ -867,9 +854,9 @@ static inline void hlist_add_head(struct hlist_node *n, struct hlist_head *h)
static inline void hlist_add_before(struct hlist_node *n,
struct hlist_node *next)
{
- WRITE_ONCE(n->pprev, next->pprev);
- WRITE_ONCE(n->next, next);
- WRITE_ONCE(next->pprev, &n->next);
+ n->pprev = next->pprev;
+ n->next = next;
+ next->pprev = &n->next;
WRITE_ONCE(*(n->pprev), n);
}
@@ -881,12 +868,12 @@ static inline void hlist_add_before(struct hlist_node *n,
static inline void hlist_add_behind(struct hlist_node *n,
struct hlist_node *prev)
{
- WRITE_ONCE(n->next, prev->next);
- WRITE_ONCE(prev->next, n);
- WRITE_ONCE(n->pprev, &prev->next);
+ n->next = prev->next;
+ prev->next = n;
+ n->pprev = &prev->next;
if (n->next)
- WRITE_ONCE(n->next->pprev, &n->next);
+ n->next->pprev = &n->next;
}
/**
--
2.20.1
next prev parent reply other threads:[~2020-03-24 15:36 UTC|newest]
Thread overview: 58+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-03-24 15:36 [RFC PATCH 00/21] Improve list integrity checking Will Deacon
2020-03-24 15:36 ` Will Deacon [this message]
2020-03-24 16:27 ` [RFC PATCH 01/21] list: Remove hlist_unhashed_lockless() Greg KH
2020-03-30 23:05 ` Paul E. McKenney
2020-03-24 15:36 ` [RFC PATCH 02/21] list: Remove hlist_nulls_unhashed_lockless() Will Deacon
2020-03-24 16:27 ` Greg KH
2020-03-30 23:07 ` Paul E. McKenney
2020-03-24 15:36 ` [RFC PATCH 03/21] list: Annotate lockless list primitives with data_race() Will Deacon
2020-03-24 16:20 ` Jann Horn
2020-03-24 16:26 ` Greg KH
2020-03-24 16:38 ` Jann Horn
2020-03-24 16:59 ` Greg KH
2020-03-24 18:22 ` Jann Horn
2020-03-24 16:23 ` Marco Elver
2020-03-24 21:33 ` Will Deacon
2020-03-31 13:10 ` Will Deacon
2020-04-01 6:34 ` Marco Elver
2020-04-01 8:40 ` Will Deacon
2020-05-08 13:46 ` [tip: locking/kcsan] kcsan: Change data_race() to no longer require marking racing accesses tip-bot2 for Marco Elver
2020-03-24 16:51 ` [RFC PATCH 03/21] list: Annotate lockless list primitives with data_race() Peter Zijlstra
2020-03-24 16:56 ` Jann Horn
2020-03-24 21:32 ` Will Deacon
2020-03-30 23:13 ` Paul E. McKenney
2020-04-24 17:39 ` Will Deacon
2020-04-27 19:24 ` Paul E. McKenney
2020-03-24 15:36 ` [RFC PATCH 04/21] timers: Use hlist_unhashed() instead of open-coding in timer_pending() Will Deacon
2020-03-24 16:30 ` Greg KH
2020-03-24 15:36 ` [RFC PATCH 05/21] list: Comment missing WRITE_ONCE() in __list_del() Will Deacon
2020-03-30 23:14 ` Paul E. McKenney
2020-03-24 15:36 ` [RFC PATCH 06/21] list: Remove superfluous WRITE_ONCE() from hlist_nulls implementation Will Deacon
2020-03-30 23:21 ` Paul E. McKenney
2020-03-24 15:36 ` [RFC PATCH 07/21] Revert "list: Use WRITE_ONCE() when adding to lists and hlists" Will Deacon
2020-03-30 23:19 ` Paul E. McKenney
2020-03-24 15:36 ` [RFC PATCH 08/21] Revert "list: Use WRITE_ONCE() when initializing list_head structures" Will Deacon
2020-03-30 23:25 ` Paul E. McKenney
2020-03-31 13:11 ` Will Deacon
2020-03-31 13:47 ` Paul E. McKenney
2020-03-24 15:36 ` [RFC PATCH 09/21] list: Remove unnecessary WRITE_ONCE() from hlist_bl_add_before() Will Deacon
2020-03-30 23:30 ` Paul E. McKenney
2020-03-31 12:37 ` Will Deacon
2020-03-24 15:36 ` [RFC PATCH 10/21] kernel-hacking: Make DEBUG_{LIST,PLIST,SG,NOTIFIERS} non-debug options Will Deacon
2020-03-24 16:42 ` Greg KH
2020-03-24 15:36 ` [RFC PATCH 11/21] list: Add integrity checking to hlist implementation Will Deacon
2020-03-24 15:36 ` [RFC PATCH 12/21] list: Poison ->next pointer for non-RCU deletion of 'hlist_nulls_node' Will Deacon
2020-03-30 23:32 ` Paul E. McKenney
2020-03-24 15:36 ` [RFC PATCH 13/21] list: Add integrity checking to hlist_nulls implementation Will Deacon
2020-03-24 15:36 ` [RFC PATCH 14/21] plist: Use CHECK_DATA_CORRUPTION instead of explicit {BUG,WARN}_ON() Will Deacon
2020-03-24 16:42 ` Greg KH
2020-03-24 15:36 ` [RFC PATCH 15/21] list_bl: Use CHECK_DATA_CORRUPTION instead of custom BUG_ON() wrapper Will Deacon
2020-03-24 15:36 ` [RFC PATCH 16/21] list_bl: Extend integrity checking in deletion routines Will Deacon
2020-03-24 15:36 ` [RFC PATCH 17/21] linux/bit_spinlock.h: Include linux/processor.h Will Deacon
2020-03-24 16:28 ` Greg KH
2020-03-24 21:08 ` Will Deacon
2020-03-24 15:36 ` [RFC PATCH 18/21] list_bl: Move integrity checking out of line Will Deacon
2020-03-24 15:36 ` [RFC PATCH 19/21] list_bl: Extend integrity checking to cover the same cases as 'hlist' Will Deacon
2020-03-24 15:36 ` [RFC PATCH 20/21] list: Format CHECK_DATA_CORRUPTION error messages consistently Will Deacon
2020-03-24 16:40 ` Greg KH
2020-03-24 15:36 ` [RFC PATCH 21/21] lkdtm: Extend list corruption checks Will Deacon
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