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* [PATCH 1/2] list: add hlist_unhashed_lockless()
@ 2019-11-07 19:37 Eric Dumazet
  2019-11-07 19:37 ` [PATCH 2/2] timer: use hlist_unhashed_lockless() in timer_pending() Eric Dumazet
  2019-11-08 19:24 ` [PATCH 1/2] list: add hlist_unhashed_lockless() Paul E. McKenney
  0 siblings, 2 replies; 9+ messages in thread
From: Eric Dumazet @ 2019-11-07 19:37 UTC (permalink / raw)
  To: Thomas Gleixner
  Cc: linux-kernel, Eric Dumazet, Eric Dumazet, Paul E. McKenney

We would like to use hlist_unhashed() from timer_pending(),
which runs without protection of a lock.

Note that other callers might also want to use this variant.

Instead of forcing a READ_ONCE() for all hlist_unhashed()
callers, add a new helper with an explicit _lockless suffix
in the name to better document what is going on.

Also add various WRITE_ONCE() in __hlist_del(), hlist_add_head()
and hlist_add_before()/hlist_add_behind() to pair with
the READ_ONCE().

Signed-off-by: Eric Dumazet <edumazet@google.com>
Cc: "Paul E. McKenney" <paulmck@kernel.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
---
 include/linux/list.h | 32 +++++++++++++++++++++-----------
 1 file changed, 21 insertions(+), 11 deletions(-)

diff --git a/include/linux/list.h b/include/linux/list.h
index 85c92555e31f85f019354e54d6efb8e79c2aee17..61f5aaf96192cdc4c1644741a415590b63c3c201 100644
--- a/include/linux/list.h
+++ b/include/linux/list.h
@@ -749,6 +749,16 @@ static inline int hlist_unhashed(const struct hlist_node *h)
 	return !h->pprev;
 }
 
+/* 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);
+}
+
 static inline int hlist_empty(const struct hlist_head *h)
 {
 	return !READ_ONCE(h->first);
@@ -761,7 +771,7 @@ static inline void __hlist_del(struct hlist_node *n)
 
 	WRITE_ONCE(*pprev, next);
 	if (next)
-		next->pprev = pprev;
+		WRITE_ONCE(next->pprev, pprev);
 }
 
 static inline void hlist_del(struct hlist_node *n)
@@ -782,32 +792,32 @@ 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;
-	n->next = first;
+	WRITE_ONCE(n->next, first);
 	if (first)
-		first->pprev = &n->next;
+		WRITE_ONCE(first->pprev, &n->next);
 	WRITE_ONCE(h->first, n);
-	n->pprev = &h->first;
+	WRITE_ONCE(n->pprev, &h->first);
 }
 
 /* next must be != NULL */
 static inline void hlist_add_before(struct hlist_node *n,
 					struct hlist_node *next)
 {
-	n->pprev = next->pprev;
-	n->next = next;
-	next->pprev = &n->next;
+	WRITE_ONCE(n->pprev, next->pprev);
+	WRITE_ONCE(n->next, next);
+	WRITE_ONCE(next->pprev, &n->next);
 	WRITE_ONCE(*(n->pprev), n);
 }
 
 static inline void hlist_add_behind(struct hlist_node *n,
 				    struct hlist_node *prev)
 {
-	n->next = prev->next;
-	prev->next = n;
-	n->pprev = &prev->next;
+	WRITE_ONCE(n->next, prev->next);
+	WRITE_ONCE(prev->next, n);
+	WRITE_ONCE(n->pprev, &prev->next);
 
 	if (n->next)
-		n->next->pprev  = &n->next;
+		WRITE_ONCE(n->next->pprev, &n->next);
 }
 
 /* after that we'll appear to be on some hlist and hlist_del will work */
-- 
2.24.0.432.g9d3f5f5b63-goog


^ permalink raw reply	[flat|nested] 9+ messages in thread

* [PATCH 2/2] timer: use hlist_unhashed_lockless() in timer_pending()
  2019-11-07 19:37 [PATCH 1/2] list: add hlist_unhashed_lockless() Eric Dumazet
@ 2019-11-07 19:37 ` Eric Dumazet
  2019-11-08 19:27   ` Paul E. McKenney
  2019-11-08 19:24 ` [PATCH 1/2] list: add hlist_unhashed_lockless() Paul E. McKenney
  1 sibling, 1 reply; 9+ messages in thread
From: Eric Dumazet @ 2019-11-07 19:37 UTC (permalink / raw)
  To: Thomas Gleixner
  Cc: linux-kernel, Eric Dumazet, Eric Dumazet, Paul E. McKenney

timer_pending() is mostly used in lockless contexts.

Without proper annotations, KCSAN might detect a data-race [1]

Using hlist_unhashed_lockless() instead of hand-coding it
seems appropriate (as suggested by Paul E. McKenney).

[1]

BUG: KCSAN: data-race in del_timer / detach_if_pending

write to 0xffff88808697d870 of 8 bytes by task 10 on cpu 0:
 __hlist_del include/linux/list.h:764 [inline]
 detach_timer kernel/time/timer.c:815 [inline]
 detach_if_pending+0xcd/0x2d0 kernel/time/timer.c:832
 try_to_del_timer_sync+0x60/0xb0 kernel/time/timer.c:1226
 del_timer_sync+0x6b/0xa0 kernel/time/timer.c:1365
 schedule_timeout+0x2d2/0x6e0 kernel/time/timer.c:1896
 rcu_gp_fqs_loop+0x37c/0x580 kernel/rcu/tree.c:1639
 rcu_gp_kthread+0x143/0x230 kernel/rcu/tree.c:1799
 kthread+0x1d4/0x200 drivers/block/aoe/aoecmd.c:1253
 ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:352

read to 0xffff88808697d870 of 8 bytes by task 12060 on cpu 1:
 del_timer+0x3b/0xb0 kernel/time/timer.c:1198
 sk_stop_timer+0x25/0x60 net/core/sock.c:2845
 inet_csk_clear_xmit_timers+0x69/0xa0 net/ipv4/inet_connection_sock.c:523
 tcp_clear_xmit_timers include/net/tcp.h:606 [inline]
 tcp_v4_destroy_sock+0xa3/0x3f0 net/ipv4/tcp_ipv4.c:2096
 inet_csk_destroy_sock+0xf4/0x250 net/ipv4/inet_connection_sock.c:836
 tcp_close+0x6f3/0x970 net/ipv4/tcp.c:2497
 inet_release+0x86/0x100 net/ipv4/af_inet.c:427
 __sock_release+0x85/0x160 net/socket.c:590
 sock_close+0x24/0x30 net/socket.c:1268
 __fput+0x1e1/0x520 fs/file_table.c:280
 ____fput+0x1f/0x30 fs/file_table.c:313
 task_work_run+0xf6/0x130 kernel/task_work.c:113
 tracehook_notify_resume include/linux/tracehook.h:188 [inline]
 exit_to_usermode_loop+0x2b4/0x2c0 arch/x86/entry/common.c:163

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 PID: 12060 Comm: syz-executor.5 Not tainted 5.4.0-rc3+ #0
Hardware name: Google Google Compute Engine/Google Compute Engine,

Signed-off-by: Eric Dumazet <edumazet@google.com>
Cc: "Paul E. McKenney" <paulmck@kernel.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
---
 include/linux/timer.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/include/linux/timer.h b/include/linux/timer.h
index 1e6650ed066d5d28251b0bd385fc37ef94c96532..0dc19a8c39c9e49a7cde3d34bfa4be8871cbc1c2 100644
--- a/include/linux/timer.h
+++ b/include/linux/timer.h
@@ -164,7 +164,7 @@ static inline void destroy_timer_on_stack(struct timer_list *timer) { }
  */
 static inline int timer_pending(const struct timer_list * timer)
 {
-	return timer->entry.pprev != NULL;
+	return !hlist_unhashed_lockless(&timer->entry);
 }
 
 extern void add_timer_on(struct timer_list *timer, int cpu);
-- 
2.24.0.432.g9d3f5f5b63-goog


^ permalink raw reply	[flat|nested] 9+ messages in thread

* Re: [PATCH 1/2] list: add hlist_unhashed_lockless()
  2019-11-07 19:37 [PATCH 1/2] list: add hlist_unhashed_lockless() Eric Dumazet
  2019-11-07 19:37 ` [PATCH 2/2] timer: use hlist_unhashed_lockless() in timer_pending() Eric Dumazet
@ 2019-11-08 19:24 ` Paul E. McKenney
  2019-11-08 20:17   ` Eric Dumazet
  1 sibling, 1 reply; 9+ messages in thread
From: Paul E. McKenney @ 2019-11-08 19:24 UTC (permalink / raw)
  To: Eric Dumazet; +Cc: Thomas Gleixner, linux-kernel, Eric Dumazet

On Thu, Nov 07, 2019 at 11:37:37AM -0800, Eric Dumazet wrote:
> We would like to use hlist_unhashed() from timer_pending(),
> which runs without protection of a lock.
> 
> Note that other callers might also want to use this variant.
> 
> Instead of forcing a READ_ONCE() for all hlist_unhashed()
> callers, add a new helper with an explicit _lockless suffix
> in the name to better document what is going on.
> 
> Also add various WRITE_ONCE() in __hlist_del(), hlist_add_head()
> and hlist_add_before()/hlist_add_behind() to pair with
> the READ_ONCE().
> 
> Signed-off-by: Eric Dumazet <edumazet@google.com>
> Cc: "Paul E. McKenney" <paulmck@kernel.org>
> Cc: Thomas Gleixner <tglx@linutronix.de>

I have queued this, but if you prefer it go some other way:

Acked-by: Paul E. McKenney <paulmck@kernel.org>

But shouldn't the uses in include/linux/rculist.h also be converted
into the patch below?  If so, I will squash the following into your
patch.

						Thanx, Paul

------------------------------------------------------------------------

diff --git a/include/linux/rculist.h b/include/linux/rculist.h
index 61c6728a..4b7ae1b 100644
--- a/include/linux/rculist.h
+++ b/include/linux/rculist.h
@@ -173,7 +173,7 @@ static inline void hlist_del_init_rcu(struct hlist_node *n)
 {
 	if (!hlist_unhashed(n)) {
 		__hlist_del(n);
-		n->pprev = NULL;
+		WRITE_ONCE(n->pprev, NULL);
 	}
 }
 
@@ -473,7 +473,7 @@ static inline void list_splice_tail_init_rcu(struct list_head *list,
 static inline void hlist_del_rcu(struct hlist_node *n)
 {
 	__hlist_del(n);
-	n->pprev = LIST_POISON2;
+	WRITE_ONCE(n->pprev, LIST_POISON2);
 }
 
 /**
@@ -489,11 +489,11 @@ static inline void hlist_replace_rcu(struct hlist_node *old,
 	struct hlist_node *next = old->next;
 
 	new->next = next;
-	new->pprev = old->pprev;
+	WRITE_ONCE(new->pprev, old->pprev);
 	rcu_assign_pointer(*(struct hlist_node __rcu **)new->pprev, new);
 	if (next)
-		new->next->pprev = &new->next;
-	old->pprev = LIST_POISON2;
+		WRITE_ONCE(new->next->pprev, &new->next);
+	WRITE_ONCE(old->pprev, LIST_POISON2);
 }
 
 /*
@@ -528,10 +528,10 @@ static inline void hlist_add_head_rcu(struct hlist_node *n,
 	struct hlist_node *first = h->first;
 
 	n->next = first;
-	n->pprev = &h->first;
+	WRITE_ONCE(n->pprev, &h->first);
 	rcu_assign_pointer(hlist_first_rcu(h), n);
 	if (first)
-		first->pprev = &n->next;
+		WRITE_ONCE(first->pprev, &n->next);
 }
 
 /**
@@ -564,7 +564,7 @@ static inline void hlist_add_tail_rcu(struct hlist_node *n,
 
 	if (last) {
 		n->next = last->next;
-		n->pprev = &last->next;
+		WRITE_ONCE(n->pprev, &last->next);
 		rcu_assign_pointer(hlist_next_rcu(last), n);
 	} else {
 		hlist_add_head_rcu(n, h);
@@ -592,10 +592,10 @@ static inline void hlist_add_tail_rcu(struct hlist_node *n,
 static inline void hlist_add_before_rcu(struct hlist_node *n,
 					struct hlist_node *next)
 {
-	n->pprev = next->pprev;
+	WRITE_ONCE(n->pprev, next->pprev);
 	n->next = next;
 	rcu_assign_pointer(hlist_pprev_rcu(n), n);
-	next->pprev = &n->next;
+	WRITE_ONCE(next->pprev, &n->next);
 }
 
 /**
@@ -620,10 +620,10 @@ static inline void hlist_add_behind_rcu(struct hlist_node *n,
 					struct hlist_node *prev)
 {
 	n->next = prev->next;
-	n->pprev = &prev->next;
+	WRITE_ONCE(n->pprev, &prev->next);
 	rcu_assign_pointer(hlist_next_rcu(prev), n);
 	if (n->next)
-		n->next->pprev = &n->next;
+		WRITE_ONCE(n->next->pprev, &n->next);
 }
 
 #define __hlist_for_each_rcu(pos, head)				\

^ permalink raw reply	[flat|nested] 9+ messages in thread

* Re: [PATCH 2/2] timer: use hlist_unhashed_lockless() in timer_pending()
  2019-11-07 19:37 ` [PATCH 2/2] timer: use hlist_unhashed_lockless() in timer_pending() Eric Dumazet
@ 2019-11-08 19:27   ` Paul E. McKenney
  0 siblings, 0 replies; 9+ messages in thread
From: Paul E. McKenney @ 2019-11-08 19:27 UTC (permalink / raw)
  To: Eric Dumazet; +Cc: Thomas Gleixner, linux-kernel, Eric Dumazet

On Thu, Nov 07, 2019 at 11:37:38AM -0800, Eric Dumazet wrote:
> timer_pending() is mostly used in lockless contexts.
> 
> Without proper annotations, KCSAN might detect a data-race [1]
> 
> Using hlist_unhashed_lockless() instead of hand-coding it
> seems appropriate (as suggested by Paul E. McKenney).
> 
> [1]
> 
> BUG: KCSAN: data-race in del_timer / detach_if_pending
> 
> write to 0xffff88808697d870 of 8 bytes by task 10 on cpu 0:
>  __hlist_del include/linux/list.h:764 [inline]
>  detach_timer kernel/time/timer.c:815 [inline]
>  detach_if_pending+0xcd/0x2d0 kernel/time/timer.c:832
>  try_to_del_timer_sync+0x60/0xb0 kernel/time/timer.c:1226
>  del_timer_sync+0x6b/0xa0 kernel/time/timer.c:1365
>  schedule_timeout+0x2d2/0x6e0 kernel/time/timer.c:1896
>  rcu_gp_fqs_loop+0x37c/0x580 kernel/rcu/tree.c:1639
>  rcu_gp_kthread+0x143/0x230 kernel/rcu/tree.c:1799
>  kthread+0x1d4/0x200 drivers/block/aoe/aoecmd.c:1253
>  ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:352
> 
> read to 0xffff88808697d870 of 8 bytes by task 12060 on cpu 1:
>  del_timer+0x3b/0xb0 kernel/time/timer.c:1198
>  sk_stop_timer+0x25/0x60 net/core/sock.c:2845
>  inet_csk_clear_xmit_timers+0x69/0xa0 net/ipv4/inet_connection_sock.c:523
>  tcp_clear_xmit_timers include/net/tcp.h:606 [inline]
>  tcp_v4_destroy_sock+0xa3/0x3f0 net/ipv4/tcp_ipv4.c:2096
>  inet_csk_destroy_sock+0xf4/0x250 net/ipv4/inet_connection_sock.c:836
>  tcp_close+0x6f3/0x970 net/ipv4/tcp.c:2497
>  inet_release+0x86/0x100 net/ipv4/af_inet.c:427
>  __sock_release+0x85/0x160 net/socket.c:590
>  sock_close+0x24/0x30 net/socket.c:1268
>  __fput+0x1e1/0x520 fs/file_table.c:280
>  ____fput+0x1f/0x30 fs/file_table.c:313
>  task_work_run+0xf6/0x130 kernel/task_work.c:113
>  tracehook_notify_resume include/linux/tracehook.h:188 [inline]
>  exit_to_usermode_loop+0x2b4/0x2c0 arch/x86/entry/common.c:163
> 
> Reported by Kernel Concurrency Sanitizer on:
> CPU: 1 PID: 12060 Comm: syz-executor.5 Not tainted 5.4.0-rc3+ #0
> Hardware name: Google Google Compute Engine/Google Compute Engine,
> 
> Signed-off-by: Eric Dumazet <edumazet@google.com>
> Cc: "Paul E. McKenney" <paulmck@kernel.org>
> Cc: Thomas Gleixner <tglx@linutronix.de>

And I queued this one as well, but again if you would prefer it go
up elsewhere, for whatever it is worth:

Acked-by: Paul E. McKenney <paulmck@kernel.org>

> ---
>  include/linux/timer.h | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/include/linux/timer.h b/include/linux/timer.h
> index 1e6650ed066d5d28251b0bd385fc37ef94c96532..0dc19a8c39c9e49a7cde3d34bfa4be8871cbc1c2 100644
> --- a/include/linux/timer.h
> +++ b/include/linux/timer.h
> @@ -164,7 +164,7 @@ static inline void destroy_timer_on_stack(struct timer_list *timer) { }
>   */
>  static inline int timer_pending(const struct timer_list * timer)
>  {
> -	return timer->entry.pprev != NULL;
> +	return !hlist_unhashed_lockless(&timer->entry);
>  }
>  
>  extern void add_timer_on(struct timer_list *timer, int cpu);
> -- 
> 2.24.0.432.g9d3f5f5b63-goog
> 

^ permalink raw reply	[flat|nested] 9+ messages in thread

* Re: [PATCH 1/2] list: add hlist_unhashed_lockless()
  2019-11-08 19:24 ` [PATCH 1/2] list: add hlist_unhashed_lockless() Paul E. McKenney
@ 2019-11-08 20:17   ` Eric Dumazet
  2019-11-08 23:42     ` Paul E. McKenney
  0 siblings, 1 reply; 9+ messages in thread
From: Eric Dumazet @ 2019-11-08 20:17 UTC (permalink / raw)
  To: Paul E. McKenney; +Cc: Thomas Gleixner, linux-kernel, Eric Dumazet

On Fri, Nov 8, 2019 at 11:24 AM Paul E. McKenney <paulmck@kernel.org> wrote:
>
> On Thu, Nov 07, 2019 at 11:37:37AM -0800, Eric Dumazet wrote:
> > We would like to use hlist_unhashed() from timer_pending(),
> > which runs without protection of a lock.
> >
> > Note that other callers might also want to use this variant.
> >
> > Instead of forcing a READ_ONCE() for all hlist_unhashed()
> > callers, add a new helper with an explicit _lockless suffix
> > in the name to better document what is going on.
> >
> > Also add various WRITE_ONCE() in __hlist_del(), hlist_add_head()
> > and hlist_add_before()/hlist_add_behind() to pair with
> > the READ_ONCE().
> >
> > Signed-off-by: Eric Dumazet <edumazet@google.com>
> > Cc: "Paul E. McKenney" <paulmck@kernel.org>
> > Cc: Thomas Gleixner <tglx@linutronix.de>
>
> I have queued this, but if you prefer it go some other way:
>
> Acked-by: Paul E. McKenney <paulmck@kernel.org>
>
> But shouldn't the uses in include/linux/rculist.h also be converted
> into the patch below?  If so, I will squash the following into your
> patch.
>
>                                                 Thanx, Paul
>
> ------------------------------------------------------------------------

Agreed, thanks for the addition of this Paul.

^ permalink raw reply	[flat|nested] 9+ messages in thread

* Re: [PATCH 1/2] list: add hlist_unhashed_lockless()
  2019-11-08 20:17   ` Eric Dumazet
@ 2019-11-08 23:42     ` Paul E. McKenney
  2019-11-09  3:15       ` Eric Dumazet
  0 siblings, 1 reply; 9+ messages in thread
From: Paul E. McKenney @ 2019-11-08 23:42 UTC (permalink / raw)
  To: Eric Dumazet; +Cc: Thomas Gleixner, linux-kernel, Eric Dumazet

On Fri, Nov 08, 2019 at 12:17:49PM -0800, Eric Dumazet wrote:
> On Fri, Nov 8, 2019 at 11:24 AM Paul E. McKenney <paulmck@kernel.org> wrote:
> >
> > On Thu, Nov 07, 2019 at 11:37:37AM -0800, Eric Dumazet wrote:
> > > We would like to use hlist_unhashed() from timer_pending(),
> > > which runs without protection of a lock.
> > >
> > > Note that other callers might also want to use this variant.
> > >
> > > Instead of forcing a READ_ONCE() for all hlist_unhashed()
> > > callers, add a new helper with an explicit _lockless suffix
> > > in the name to better document what is going on.
> > >
> > > Also add various WRITE_ONCE() in __hlist_del(), hlist_add_head()
> > > and hlist_add_before()/hlist_add_behind() to pair with
> > > the READ_ONCE().
> > >
> > > Signed-off-by: Eric Dumazet <edumazet@google.com>
> > > Cc: "Paul E. McKenney" <paulmck@kernel.org>
> > > Cc: Thomas Gleixner <tglx@linutronix.de>
> >
> > I have queued this, but if you prefer it go some other way:
> >
> > Acked-by: Paul E. McKenney <paulmck@kernel.org>
> >
> > But shouldn't the uses in include/linux/rculist.h also be converted
> > into the patch below?  If so, I will squash the following into your
> > patch.
> >
> >                                                 Thanx, Paul
> >
> > ------------------------------------------------------------------------
> 
> Agreed, thanks for the addition of this Paul.

Very good, squashed and pushed, thank you!

							Thanx, Paul

^ permalink raw reply	[flat|nested] 9+ messages in thread

* Re: [PATCH 1/2] list: add hlist_unhashed_lockless()
  2019-11-08 23:42     ` Paul E. McKenney
@ 2019-11-09  3:15       ` Eric Dumazet
  2019-11-09 17:54         ` Paul E. McKenney
  0 siblings, 1 reply; 9+ messages in thread
From: Eric Dumazet @ 2019-11-09  3:15 UTC (permalink / raw)
  To: Paul E. McKenney; +Cc: Thomas Gleixner, linux-kernel, Eric Dumazet

On Fri, Nov 8, 2019 at 3:42 PM Paul E. McKenney <paulmck@kernel.org> wrote:
>
> On Fri, Nov 08, 2019 at 12:17:49PM -0800, Eric Dumazet wrote:
> > On Fri, Nov 8, 2019 at 11:24 AM Paul E. McKenney <paulmck@kernel.org> wrote:
> > >
> > > On Thu, Nov 07, 2019 at 11:37:37AM -0800, Eric Dumazet wrote:
> > > > We would like to use hlist_unhashed() from timer_pending(),
> > > > which runs without protection of a lock.
> > > >
> > > > Note that other callers might also want to use this variant.
> > > >
> > > > Instead of forcing a READ_ONCE() for all hlist_unhashed()
> > > > callers, add a new helper with an explicit _lockless suffix
> > > > in the name to better document what is going on.
> > > >
> > > > Also add various WRITE_ONCE() in __hlist_del(), hlist_add_head()
> > > > and hlist_add_before()/hlist_add_behind() to pair with
> > > > the READ_ONCE().
> > > >
> > > > Signed-off-by: Eric Dumazet <edumazet@google.com>
> > > > Cc: "Paul E. McKenney" <paulmck@kernel.org>
> > > > Cc: Thomas Gleixner <tglx@linutronix.de>
> > >
> > > I have queued this, but if you prefer it go some other way:
> > >
> > > Acked-by: Paul E. McKenney <paulmck@kernel.org>
> > >
> > > But shouldn't the uses in include/linux/rculist.h also be converted
> > > into the patch below?  If so, I will squash the following into your
> > > patch.
> > >
> > >                                                 Thanx, Paul
> > >
> > > ------------------------------------------------------------------------
> >
> > Agreed, thanks for the addition of this Paul.
>
> Very good, squashed and pushed, thank you!
>

I have another KCSAN report of a bug that will force us to use
hlist_unhashed_lockless() from sk_unhashed()

(Meaning we also need to add some WRITE_ONCE() annotations to
include/linux/list_nulls.h )

BUG: KCSAN: data-race in inet_unhash / inet_unhash

write to 0xffff8880a69a0170 of 8 bytes by interrupt on cpu 1:
 __hlist_nulls_del include/linux/list_nulls.h:88 [inline]
 hlist_nulls_del_init_rcu include/linux/rculist_nulls.h:36 [inline]
 __sk_nulls_del_node_init_rcu include/net/sock.h:676 [inline]
 inet_unhash+0x38f/0x4a0 net/ipv4/inet_hashtables.c:612
 tcp_set_state+0xfa/0x3e0 net/ipv4/tcp.c:2249
 tcp_done+0x93/0x1e0 net/ipv4/tcp.c:3854
 tcp_write_err+0x7e/0xc0 net/ipv4/tcp_timer.c:56
 tcp_retransmit_timer+0x9b8/0x16d0 net/ipv4/tcp_timer.c:479
 tcp_write_timer_handler+0x42d/0x510 net/ipv4/tcp_timer.c:599
 tcp_write_timer+0xd1/0xf0 net/ipv4/tcp_timer.c:619
 call_timer_fn+0x5f/0x2f0 kernel/time/timer.c:1404
 expire_timers kernel/time/timer.c:1449 [inline]
 __run_timers kernel/time/timer.c:1773 [inline]
 __run_timers kernel/time/timer.c:1740 [inline]
 run_timer_softirq+0xc0c/0xcd0 kernel/time/timer.c:1786
 __do_softirq+0x115/0x33f kernel/softirq.c:292
 invoke_softirq kernel/softirq.c:373 [inline]
 irq_exit+0xbb/0xe0 kernel/softirq.c:413
 exiting_irq arch/x86/include/asm/apic.h:536 [inline]
 smp_apic_timer_interrupt+0xe6/0x280 arch/x86/kernel/apic/apic.c:1137
 apic_timer_interrupt+0xf/0x20 arch/x86/entry/entry_64.S:830
 native_safe_halt+0xe/0x10 arch/x86/kernel/paravirt.c:71
 arch_cpu_idle+0x1f/0x30 arch/x86/kernel/process.c:571
 default_idle_call+0x1e/0x40 kernel/sched/idle.c:94
 cpuidle_idle_call kernel/sched/idle.c:154 [inline]
 do_idle+0x1af/0x280 kernel/sched/idle.c:263
 cpu_startup_entry+0x1b/0x20 kernel/sched/idle.c:355
 start_secondary+0x208/0x260 arch/x86/kernel/smpboot.c:264
 secondary_startup_64+0xa4/0xb0 arch/x86/kernel/head_64.S:241

read to 0xffff8880a69a0170 of 8 bytes by interrupt on cpu 0:
 sk_unhashed include/net/sock.h:607 [inline]
 inet_unhash+0x3d/0x4a0 net/ipv4/inet_hashtables.c:592
 tcp_set_state+0xfa/0x3e0 net/ipv4/tcp.c:2249
 tcp_done+0x93/0x1e0 net/ipv4/tcp.c:3854
 tcp_write_err+0x7e/0xc0 net/ipv4/tcp_timer.c:56
 tcp_retransmit_timer+0x9b8/0x16d0 net/ipv4/tcp_timer.c:479
 tcp_write_timer_handler+0x42d/0x510 net/ipv4/tcp_timer.c:599
 tcp_write_timer+0xd1/0xf0 net/ipv4/tcp_timer.c:619
 call_timer_fn+0x5f/0x2f0 kernel/time/timer.c:1404
 expire_timers kernel/time/timer.c:1449 [inline]
 __run_timers kernel/time/timer.c:1773 [inline]
 __run_timers kernel/time/timer.c:1740 [inline]
 run_timer_softirq+0xc0c/0xcd0 kernel/time/timer.c:1786
 __do_softirq+0x115/0x33f kernel/softirq.c:292
 invoke_softirq kernel/softirq.c:373 [inline]
 irq_exit+0xbb/0xe0 kernel/softirq.c:413
 exiting_irq arch/x86/include/asm/apic.h:536 [inline]
 smp_apic_timer_interrupt+0xe6/0x280 arch/x86/kernel/apic/apic.c:1137
 apic_timer_interrupt+0xf/0x20 arch/x86/entry/entry_64.S:830
 native_safe_halt+0xe/0x10 arch/x86/kernel/paravirt.c:71
 arch_cpu_idle+0x1f/0x30 arch/x86/kernel/process.c:571
 default_idle_call+0x1e/0x40 kernel/sched/idle.c:94
 cpuidle_idle_call kernel/sched/idle.c:154 [inline]
 do_idle+0x1af/0x280 kernel/sched/idle.c:263
 cpu_startup_entry+0x1b/0x20 kernel/sched/idle.c:355
 rest_init+0xec/0xf6 init/main.c:452
 arch_call_rest_init+0x17/0x37
 start_kernel+0x838/0x85e init/main.c:786
 x86_64_start_reservations+0x29/0x2b arch/x86/kernel/head64.c:490
 x86_64_start_kernel+0x72/0x76 arch/x86/kernel/head64.c:471
 secondary_startup_64+0xa4/0xb0 arch/x86/kernel/head_64.S:241

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 PID: 0 Comm: swapper/0 Not tainted 5.4.0-rc6+ #0
Hardware name: Google Google Compute Engine/Google Compute Engine,
BIOS Google 01/01/2011

^ permalink raw reply	[flat|nested] 9+ messages in thread

* Re: [PATCH 1/2] list: add hlist_unhashed_lockless()
  2019-11-09  3:15       ` Eric Dumazet
@ 2019-11-09 17:54         ` Paul E. McKenney
  2019-11-09 18:53           ` Paul E. McKenney
  0 siblings, 1 reply; 9+ messages in thread
From: Paul E. McKenney @ 2019-11-09 17:54 UTC (permalink / raw)
  To: Eric Dumazet; +Cc: Thomas Gleixner, linux-kernel, Eric Dumazet

On Fri, Nov 08, 2019 at 07:15:16PM -0800, Eric Dumazet wrote:
> On Fri, Nov 8, 2019 at 3:42 PM Paul E. McKenney <paulmck@kernel.org> wrote:
> >
> > On Fri, Nov 08, 2019 at 12:17:49PM -0800, Eric Dumazet wrote:
> > > On Fri, Nov 8, 2019 at 11:24 AM Paul E. McKenney <paulmck@kernel.org> wrote:
> > > >
> > > > On Thu, Nov 07, 2019 at 11:37:37AM -0800, Eric Dumazet wrote:
> > > > > We would like to use hlist_unhashed() from timer_pending(),
> > > > > which runs without protection of a lock.
> > > > >
> > > > > Note that other callers might also want to use this variant.
> > > > >
> > > > > Instead of forcing a READ_ONCE() for all hlist_unhashed()
> > > > > callers, add a new helper with an explicit _lockless suffix
> > > > > in the name to better document what is going on.
> > > > >
> > > > > Also add various WRITE_ONCE() in __hlist_del(), hlist_add_head()
> > > > > and hlist_add_before()/hlist_add_behind() to pair with
> > > > > the READ_ONCE().
> > > > >
> > > > > Signed-off-by: Eric Dumazet <edumazet@google.com>
> > > > > Cc: "Paul E. McKenney" <paulmck@kernel.org>
> > > > > Cc: Thomas Gleixner <tglx@linutronix.de>
> > > >
> > > > I have queued this, but if you prefer it go some other way:
> > > >
> > > > Acked-by: Paul E. McKenney <paulmck@kernel.org>
> > > >
> > > > But shouldn't the uses in include/linux/rculist.h also be converted
> > > > into the patch below?  If so, I will squash the following into your
> > > > patch.
> > > >
> > > >                                                 Thanx, Paul
> > > >
> > > > ------------------------------------------------------------------------
> > >
> > > Agreed, thanks for the addition of this Paul.
> >
> > Very good, squashed and pushed, thank you!
> >
> 
> I have another KCSAN report of a bug that will force us to use
> hlist_unhashed_lockless() from sk_unhashed()
> 
> (Meaning we also need to add some WRITE_ONCE() annotations to
> include/linux/list_nulls.h )
> 
> BUG: KCSAN: data-race in inet_unhash / inet_unhash
> 
> write to 0xffff8880a69a0170 of 8 bytes by interrupt on cpu 1:
>  __hlist_nulls_del include/linux/list_nulls.h:88 [inline]
>  hlist_nulls_del_init_rcu include/linux/rculist_nulls.h:36 [inline]
>  __sk_nulls_del_node_init_rcu include/net/sock.h:676 [inline]
>  inet_unhash+0x38f/0x4a0 net/ipv4/inet_hashtables.c:612
>  tcp_set_state+0xfa/0x3e0 net/ipv4/tcp.c:2249
>  tcp_done+0x93/0x1e0 net/ipv4/tcp.c:3854
>  tcp_write_err+0x7e/0xc0 net/ipv4/tcp_timer.c:56
>  tcp_retransmit_timer+0x9b8/0x16d0 net/ipv4/tcp_timer.c:479
>  tcp_write_timer_handler+0x42d/0x510 net/ipv4/tcp_timer.c:599
>  tcp_write_timer+0xd1/0xf0 net/ipv4/tcp_timer.c:619
>  call_timer_fn+0x5f/0x2f0 kernel/time/timer.c:1404
>  expire_timers kernel/time/timer.c:1449 [inline]
>  __run_timers kernel/time/timer.c:1773 [inline]
>  __run_timers kernel/time/timer.c:1740 [inline]
>  run_timer_softirq+0xc0c/0xcd0 kernel/time/timer.c:1786
>  __do_softirq+0x115/0x33f kernel/softirq.c:292
>  invoke_softirq kernel/softirq.c:373 [inline]
>  irq_exit+0xbb/0xe0 kernel/softirq.c:413
>  exiting_irq arch/x86/include/asm/apic.h:536 [inline]
>  smp_apic_timer_interrupt+0xe6/0x280 arch/x86/kernel/apic/apic.c:1137
>  apic_timer_interrupt+0xf/0x20 arch/x86/entry/entry_64.S:830
>  native_safe_halt+0xe/0x10 arch/x86/kernel/paravirt.c:71
>  arch_cpu_idle+0x1f/0x30 arch/x86/kernel/process.c:571
>  default_idle_call+0x1e/0x40 kernel/sched/idle.c:94
>  cpuidle_idle_call kernel/sched/idle.c:154 [inline]
>  do_idle+0x1af/0x280 kernel/sched/idle.c:263
>  cpu_startup_entry+0x1b/0x20 kernel/sched/idle.c:355
>  start_secondary+0x208/0x260 arch/x86/kernel/smpboot.c:264
>  secondary_startup_64+0xa4/0xb0 arch/x86/kernel/head_64.S:241
> 
> read to 0xffff8880a69a0170 of 8 bytes by interrupt on cpu 0:
>  sk_unhashed include/net/sock.h:607 [inline]
>  inet_unhash+0x3d/0x4a0 net/ipv4/inet_hashtables.c:592
>  tcp_set_state+0xfa/0x3e0 net/ipv4/tcp.c:2249
>  tcp_done+0x93/0x1e0 net/ipv4/tcp.c:3854
>  tcp_write_err+0x7e/0xc0 net/ipv4/tcp_timer.c:56
>  tcp_retransmit_timer+0x9b8/0x16d0 net/ipv4/tcp_timer.c:479
>  tcp_write_timer_handler+0x42d/0x510 net/ipv4/tcp_timer.c:599
>  tcp_write_timer+0xd1/0xf0 net/ipv4/tcp_timer.c:619
>  call_timer_fn+0x5f/0x2f0 kernel/time/timer.c:1404
>  expire_timers kernel/time/timer.c:1449 [inline]
>  __run_timers kernel/time/timer.c:1773 [inline]
>  __run_timers kernel/time/timer.c:1740 [inline]
>  run_timer_softirq+0xc0c/0xcd0 kernel/time/timer.c:1786
>  __do_softirq+0x115/0x33f kernel/softirq.c:292
>  invoke_softirq kernel/softirq.c:373 [inline]
>  irq_exit+0xbb/0xe0 kernel/softirq.c:413
>  exiting_irq arch/x86/include/asm/apic.h:536 [inline]
>  smp_apic_timer_interrupt+0xe6/0x280 arch/x86/kernel/apic/apic.c:1137
>  apic_timer_interrupt+0xf/0x20 arch/x86/entry/entry_64.S:830
>  native_safe_halt+0xe/0x10 arch/x86/kernel/paravirt.c:71
>  arch_cpu_idle+0x1f/0x30 arch/x86/kernel/process.c:571
>  default_idle_call+0x1e/0x40 kernel/sched/idle.c:94
>  cpuidle_idle_call kernel/sched/idle.c:154 [inline]
>  do_idle+0x1af/0x280 kernel/sched/idle.c:263
>  cpu_startup_entry+0x1b/0x20 kernel/sched/idle.c:355
>  rest_init+0xec/0xf6 init/main.c:452
>  arch_call_rest_init+0x17/0x37
>  start_kernel+0x838/0x85e init/main.c:786
>  x86_64_start_reservations+0x29/0x2b arch/x86/kernel/head64.c:490
>  x86_64_start_kernel+0x72/0x76 arch/x86/kernel/head64.c:471
>  secondary_startup_64+0xa4/0xb0 arch/x86/kernel/head_64.S:241
> 
> Reported by Kernel Concurrency Sanitizer on:
> CPU: 0 PID: 0 Comm: swapper/0 Not tainted 5.4.0-rc6+ #0
> Hardware name: Google Google Compute Engine/Google Compute Engine,
> BIOS Google 01/01/2011

Like this?

						Thanx, Paul

------------------------------------------------------------------------

commit fef2da9c0cfa4f9ec405ff059fceb00d29de34dc
Author: Paul E. McKenney <paulmck@kernel.org>
Date:   Sat Nov 9 09:42:13 2019 -0800

    rcu: Use WRITE_ONCE() for assignments to ->pprev for hlist_nulls
    
    Eric Dumazet supplied a KCSAN report of a bug that forces use
    of hlist_unhashed_lockless() from sk_unhashed():
    
    ------------------------------------------------------------------------
    
    BUG: KCSAN: data-race in inet_unhash / inet_unhash
    
    write to 0xffff8880a69a0170 of 8 bytes by interrupt on cpu 1:
     __hlist_nulls_del include/linux/list_nulls.h:88 [inline]
     hlist_nulls_del_init_rcu include/linux/rculist_nulls.h:36 [inline]
     __sk_nulls_del_node_init_rcu include/net/sock.h:676 [inline]
     inet_unhash+0x38f/0x4a0 net/ipv4/inet_hashtables.c:612
     tcp_set_state+0xfa/0x3e0 net/ipv4/tcp.c:2249
     tcp_done+0x93/0x1e0 net/ipv4/tcp.c:3854
     tcp_write_err+0x7e/0xc0 net/ipv4/tcp_timer.c:56
     tcp_retransmit_timer+0x9b8/0x16d0 net/ipv4/tcp_timer.c:479
     tcp_write_timer_handler+0x42d/0x510 net/ipv4/tcp_timer.c:599
     tcp_write_timer+0xd1/0xf0 net/ipv4/tcp_timer.c:619
     call_timer_fn+0x5f/0x2f0 kernel/time/timer.c:1404
     expire_timers kernel/time/timer.c:1449 [inline]
     __run_timers kernel/time/timer.c:1773 [inline]
     __run_timers kernel/time/timer.c:1740 [inline]
     run_timer_softirq+0xc0c/0xcd0 kernel/time/timer.c:1786
     __do_softirq+0x115/0x33f kernel/softirq.c:292
     invoke_softirq kernel/softirq.c:373 [inline]
     irq_exit+0xbb/0xe0 kernel/softirq.c:413
     exiting_irq arch/x86/include/asm/apic.h:536 [inline]
     smp_apic_timer_interrupt+0xe6/0x280 arch/x86/kernel/apic/apic.c:1137
     apic_timer_interrupt+0xf/0x20 arch/x86/entry/entry_64.S:830
     native_safe_halt+0xe/0x10 arch/x86/kernel/paravirt.c:71
     arch_cpu_idle+0x1f/0x30 arch/x86/kernel/process.c:571
     default_idle_call+0x1e/0x40 kernel/sched/idle.c:94
     cpuidle_idle_call kernel/sched/idle.c:154 [inline]
     do_idle+0x1af/0x280 kernel/sched/idle.c:263
     cpu_startup_entry+0x1b/0x20 kernel/sched/idle.c:355
     start_secondary+0x208/0x260 arch/x86/kernel/smpboot.c:264
     secondary_startup_64+0xa4/0xb0 arch/x86/kernel/head_64.S:241
    
    read to 0xffff8880a69a0170 of 8 bytes by interrupt on cpu 0:
     sk_unhashed include/net/sock.h:607 [inline]
     inet_unhash+0x3d/0x4a0 net/ipv4/inet_hashtables.c:592
     tcp_set_state+0xfa/0x3e0 net/ipv4/tcp.c:2249
     tcp_done+0x93/0x1e0 net/ipv4/tcp.c:3854
     tcp_write_err+0x7e/0xc0 net/ipv4/tcp_timer.c:56
     tcp_retransmit_timer+0x9b8/0x16d0 net/ipv4/tcp_timer.c:479
     tcp_write_timer_handler+0x42d/0x510 net/ipv4/tcp_timer.c:599
     tcp_write_timer+0xd1/0xf0 net/ipv4/tcp_timer.c:619
     call_timer_fn+0x5f/0x2f0 kernel/time/timer.c:1404
     expire_timers kernel/time/timer.c:1449 [inline]
     __run_timers kernel/time/timer.c:1773 [inline]
     __run_timers kernel/time/timer.c:1740 [inline]
     run_timer_softirq+0xc0c/0xcd0 kernel/time/timer.c:1786
     __do_softirq+0x115/0x33f kernel/softirq.c:292
     invoke_softirq kernel/softirq.c:373 [inline]
     irq_exit+0xbb/0xe0 kernel/softirq.c:413
     exiting_irq arch/x86/include/asm/apic.h:536 [inline]
     smp_apic_timer_interrupt+0xe6/0x280 arch/x86/kernel/apic/apic.c:1137
     apic_timer_interrupt+0xf/0x20 arch/x86/entry/entry_64.S:830
     native_safe_halt+0xe/0x10 arch/x86/kernel/paravirt.c:71
     arch_cpu_idle+0x1f/0x30 arch/x86/kernel/process.c:571
     default_idle_call+0x1e/0x40 kernel/sched/idle.c:94
     cpuidle_idle_call kernel/sched/idle.c:154 [inline]
     do_idle+0x1af/0x280 kernel/sched/idle.c:263
     cpu_startup_entry+0x1b/0x20 kernel/sched/idle.c:355
     rest_init+0xec/0xf6 init/main.c:452
     arch_call_rest_init+0x17/0x37
     start_kernel+0x838/0x85e init/main.c:786
     x86_64_start_reservations+0x29/0x2b arch/x86/kernel/head64.c:490
     x86_64_start_kernel+0x72/0x76 arch/x86/kernel/head64.c:471
     secondary_startup_64+0xa4/0xb0 arch/x86/kernel/head_64.S:241
    
    Reported by Kernel Concurrency Sanitizer on:
    CPU: 0 PID: 0 Comm: swapper/0 Not tainted 5.4.0-rc6+ #0
    Hardware name: Google Google Compute Engine/Google Compute Engine,
    BIOS Google 01/01/2011
    
    ------------------------------------------------------------------------
    
    This commit therefore replaces C-language assignments with WRITE_ONCE()
    in include/linux/list_nulls.h and include/linux/rculist_nulls.h.
    
    Reported-by: Eric Dumazet <edumazet@google.com> # For KCSAN
    Signed-off-by: Paul E. McKenney <paulmck@kernel.org>

diff --git a/include/linux/list_nulls.h b/include/linux/list_nulls.h
index 3ef9674..1ecd356 100644
--- a/include/linux/list_nulls.h
+++ b/include/linux/list_nulls.h
@@ -72,10 +72,10 @@ static inline void hlist_nulls_add_head(struct hlist_nulls_node *n,
 	struct hlist_nulls_node *first = h->first;
 
 	n->next = first;
-	n->pprev = &h->first;
+	WRITE_ONCE(n->pprev, &h->first);
 	h->first = n;
 	if (!is_a_nulls(first))
-		first->pprev = &n->next;
+		WRITE_ONCE(first->pprev, &n->next);
 }
 
 static inline void __hlist_nulls_del(struct hlist_nulls_node *n)
@@ -85,13 +85,13 @@ static inline void __hlist_nulls_del(struct hlist_nulls_node *n)
 
 	WRITE_ONCE(*pprev, next);
 	if (!is_a_nulls(next))
-		next->pprev = pprev;
+		WRITE_ONCE(next->pprev, pprev);
 }
 
 static inline void hlist_nulls_del(struct hlist_nulls_node *n)
 {
 	__hlist_nulls_del(n);
-	n->pprev = LIST_POISON2;
+	WRITE_ONCE(n->pprev, LIST_POISON2);
 }
 
 /**
diff --git a/include/linux/rculist_nulls.h b/include/linux/rculist_nulls.h
index bc8206a..517a06f 100644
--- a/include/linux/rculist_nulls.h
+++ b/include/linux/rculist_nulls.h
@@ -34,7 +34,7 @@ static inline void hlist_nulls_del_init_rcu(struct hlist_nulls_node *n)
 {
 	if (!hlist_nulls_unhashed(n)) {
 		__hlist_nulls_del(n);
-		n->pprev = NULL;
+		WRITE_ONCE(n->pprev, NULL);
 	}
 }
 
@@ -66,7 +66,7 @@ static inline void hlist_nulls_del_init_rcu(struct hlist_nulls_node *n)
 static inline void hlist_nulls_del_rcu(struct hlist_nulls_node *n)
 {
 	__hlist_nulls_del(n);
-	n->pprev = LIST_POISON2;
+	WRITE_ONCE(n->pprev, LIST_POISON2);
 }
 
 /**
@@ -94,10 +94,10 @@ static inline void hlist_nulls_add_head_rcu(struct hlist_nulls_node *n,
 	struct hlist_nulls_node *first = h->first;
 
 	n->next = first;
-	n->pprev = &h->first;
+	WRITE_ONCE(n->pprev, &h->first);
 	rcu_assign_pointer(hlist_nulls_first_rcu(h), n);
 	if (!is_a_nulls(first))
-		first->pprev = &n->next;
+		WRITE_ONCE(first->pprev, &n->next);
 }
 
 /**

^ permalink raw reply	[flat|nested] 9+ messages in thread

* Re: [PATCH 1/2] list: add hlist_unhashed_lockless()
  2019-11-09 17:54         ` Paul E. McKenney
@ 2019-11-09 18:53           ` Paul E. McKenney
  0 siblings, 0 replies; 9+ messages in thread
From: Paul E. McKenney @ 2019-11-09 18:53 UTC (permalink / raw)
  To: Eric Dumazet; +Cc: Thomas Gleixner, linux-kernel, Eric Dumazet

On Sat, Nov 09, 2019 at 09:54:40AM -0800, Paul E. McKenney wrote:
> On Fri, Nov 08, 2019 at 07:15:16PM -0800, Eric Dumazet wrote:
> > On Fri, Nov 8, 2019 at 3:42 PM Paul E. McKenney <paulmck@kernel.org> wrote:
> > >
> > > On Fri, Nov 08, 2019 at 12:17:49PM -0800, Eric Dumazet wrote:
> > > > On Fri, Nov 8, 2019 at 11:24 AM Paul E. McKenney <paulmck@kernel.org> wrote:
> > > > >
> > > > > On Thu, Nov 07, 2019 at 11:37:37AM -0800, Eric Dumazet wrote:
> > > > > > We would like to use hlist_unhashed() from timer_pending(),
> > > > > > which runs without protection of a lock.
> > > > > >
> > > > > > Note that other callers might also want to use this variant.
> > > > > >
> > > > > > Instead of forcing a READ_ONCE() for all hlist_unhashed()
> > > > > > callers, add a new helper with an explicit _lockless suffix
> > > > > > in the name to better document what is going on.
> > > > > >
> > > > > > Also add various WRITE_ONCE() in __hlist_del(), hlist_add_head()
> > > > > > and hlist_add_before()/hlist_add_behind() to pair with
> > > > > > the READ_ONCE().
> > > > > >
> > > > > > Signed-off-by: Eric Dumazet <edumazet@google.com>
> > > > > > Cc: "Paul E. McKenney" <paulmck@kernel.org>
> > > > > > Cc: Thomas Gleixner <tglx@linutronix.de>
> > > > >
> > > > > I have queued this, but if you prefer it go some other way:
> > > > >
> > > > > Acked-by: Paul E. McKenney <paulmck@kernel.org>
> > > > >
> > > > > But shouldn't the uses in include/linux/rculist.h also be converted
> > > > > into the patch below?  If so, I will squash the following into your
> > > > > patch.
> > > > >
> > > > >                                                 Thanx, Paul
> > > > >
> > > > > ------------------------------------------------------------------------
> > > >
> > > > Agreed, thanks for the addition of this Paul.
> > >
> > > Very good, squashed and pushed, thank you!
> > >
> > 
> > I have another KCSAN report of a bug that will force us to use
> > hlist_unhashed_lockless() from sk_unhashed()
> > 
> > (Meaning we also need to add some WRITE_ONCE() annotations to
> > include/linux/list_nulls.h )
> > 
> > BUG: KCSAN: data-race in inet_unhash / inet_unhash
> > 
> > write to 0xffff8880a69a0170 of 8 bytes by interrupt on cpu 1:
> >  __hlist_nulls_del include/linux/list_nulls.h:88 [inline]
> >  hlist_nulls_del_init_rcu include/linux/rculist_nulls.h:36 [inline]
> >  __sk_nulls_del_node_init_rcu include/net/sock.h:676 [inline]
> >  inet_unhash+0x38f/0x4a0 net/ipv4/inet_hashtables.c:612
> >  tcp_set_state+0xfa/0x3e0 net/ipv4/tcp.c:2249
> >  tcp_done+0x93/0x1e0 net/ipv4/tcp.c:3854
> >  tcp_write_err+0x7e/0xc0 net/ipv4/tcp_timer.c:56
> >  tcp_retransmit_timer+0x9b8/0x16d0 net/ipv4/tcp_timer.c:479
> >  tcp_write_timer_handler+0x42d/0x510 net/ipv4/tcp_timer.c:599
> >  tcp_write_timer+0xd1/0xf0 net/ipv4/tcp_timer.c:619
> >  call_timer_fn+0x5f/0x2f0 kernel/time/timer.c:1404
> >  expire_timers kernel/time/timer.c:1449 [inline]
> >  __run_timers kernel/time/timer.c:1773 [inline]
> >  __run_timers kernel/time/timer.c:1740 [inline]
> >  run_timer_softirq+0xc0c/0xcd0 kernel/time/timer.c:1786
> >  __do_softirq+0x115/0x33f kernel/softirq.c:292
> >  invoke_softirq kernel/softirq.c:373 [inline]
> >  irq_exit+0xbb/0xe0 kernel/softirq.c:413
> >  exiting_irq arch/x86/include/asm/apic.h:536 [inline]
> >  smp_apic_timer_interrupt+0xe6/0x280 arch/x86/kernel/apic/apic.c:1137
> >  apic_timer_interrupt+0xf/0x20 arch/x86/entry/entry_64.S:830
> >  native_safe_halt+0xe/0x10 arch/x86/kernel/paravirt.c:71
> >  arch_cpu_idle+0x1f/0x30 arch/x86/kernel/process.c:571
> >  default_idle_call+0x1e/0x40 kernel/sched/idle.c:94
> >  cpuidle_idle_call kernel/sched/idle.c:154 [inline]
> >  do_idle+0x1af/0x280 kernel/sched/idle.c:263
> >  cpu_startup_entry+0x1b/0x20 kernel/sched/idle.c:355
> >  start_secondary+0x208/0x260 arch/x86/kernel/smpboot.c:264
> >  secondary_startup_64+0xa4/0xb0 arch/x86/kernel/head_64.S:241
> > 
> > read to 0xffff8880a69a0170 of 8 bytes by interrupt on cpu 0:
> >  sk_unhashed include/net/sock.h:607 [inline]
> >  inet_unhash+0x3d/0x4a0 net/ipv4/inet_hashtables.c:592
> >  tcp_set_state+0xfa/0x3e0 net/ipv4/tcp.c:2249
> >  tcp_done+0x93/0x1e0 net/ipv4/tcp.c:3854
> >  tcp_write_err+0x7e/0xc0 net/ipv4/tcp_timer.c:56
> >  tcp_retransmit_timer+0x9b8/0x16d0 net/ipv4/tcp_timer.c:479
> >  tcp_write_timer_handler+0x42d/0x510 net/ipv4/tcp_timer.c:599
> >  tcp_write_timer+0xd1/0xf0 net/ipv4/tcp_timer.c:619
> >  call_timer_fn+0x5f/0x2f0 kernel/time/timer.c:1404
> >  expire_timers kernel/time/timer.c:1449 [inline]
> >  __run_timers kernel/time/timer.c:1773 [inline]
> >  __run_timers kernel/time/timer.c:1740 [inline]
> >  run_timer_softirq+0xc0c/0xcd0 kernel/time/timer.c:1786
> >  __do_softirq+0x115/0x33f kernel/softirq.c:292
> >  invoke_softirq kernel/softirq.c:373 [inline]
> >  irq_exit+0xbb/0xe0 kernel/softirq.c:413
> >  exiting_irq arch/x86/include/asm/apic.h:536 [inline]
> >  smp_apic_timer_interrupt+0xe6/0x280 arch/x86/kernel/apic/apic.c:1137
> >  apic_timer_interrupt+0xf/0x20 arch/x86/entry/entry_64.S:830
> >  native_safe_halt+0xe/0x10 arch/x86/kernel/paravirt.c:71
> >  arch_cpu_idle+0x1f/0x30 arch/x86/kernel/process.c:571
> >  default_idle_call+0x1e/0x40 kernel/sched/idle.c:94
> >  cpuidle_idle_call kernel/sched/idle.c:154 [inline]
> >  do_idle+0x1af/0x280 kernel/sched/idle.c:263
> >  cpu_startup_entry+0x1b/0x20 kernel/sched/idle.c:355
> >  rest_init+0xec/0xf6 init/main.c:452
> >  arch_call_rest_init+0x17/0x37
> >  start_kernel+0x838/0x85e init/main.c:786
> >  x86_64_start_reservations+0x29/0x2b arch/x86/kernel/head64.c:490
> >  x86_64_start_kernel+0x72/0x76 arch/x86/kernel/head64.c:471
> >  secondary_startup_64+0xa4/0xb0 arch/x86/kernel/head_64.S:241
> > 
> > Reported by Kernel Concurrency Sanitizer on:
> > CPU: 0 PID: 0 Comm: swapper/0 Not tainted 5.4.0-rc6+ #0
> > Hardware name: Google Google Compute Engine/Google Compute Engine,
> > BIOS Google 01/01/2011
> 
> Like this?

Hmmm...  Do you also need this?

						Thanx, Paul

------------------------------------------------------------------------

commit cf78c8772c9dc26a36c0e5eae1262cc396bbfb3f
Author: Paul E. McKenney <paulmck@kernel.org>
Date:   Sat Nov 9 10:45:47 2019 -0800

    rcu: Add a hlist_nulls_unhashed_lockless() function
    
    This commit adds an hlist_nulls_unhashed_lockless() to allow lockless
    checking for whether or note an hlist_nulls_node is hashed or not.
    While in the area, this commit also adds a docbook comment to the existing
    hlist_nulls_unhashed() function.
    
    Signed-off-by: Paul E. McKenney <paulmck@kernel.org>

diff --git a/include/linux/list_nulls.h b/include/linux/list_nulls.h
index 1ecd356..fa6e847 100644
--- a/include/linux/list_nulls.h
+++ b/include/linux/list_nulls.h
@@ -56,11 +56,33 @@ static inline unsigned long get_nulls_value(const struct hlist_nulls_node *ptr)
 	return ((unsigned long)ptr) >> 1;
 }
 
+/**
+ * hlist_nulls_unhashed - Has node been removed and reinitialized?
+ * @h: Node to be checked
+ *
+ * Not that not all removal functions will leave a node in unhashed state.
+ * For example, hlist_del_init_rcu() leaves the node in unhashed state,
+ * but hlist_nulls_del() does not.
+ */
 static inline int hlist_nulls_unhashed(const struct hlist_nulls_node *h)
 {
 	return !h->pprev;
 }
 
+/**
+ * hlist_nulls_unhashed_lockless - Has node been removed and reinitialized?
+ * @h: Node to be checked
+ *
+ * Not that not all removal functions will leave a node in unhashed state.
+ * For example, hlist_del_init_rcu() leaves the node in unhashed state,
+ * but hlist_nulls_del() does not.  Unlike hlist_nulls_unhashed(), this
+ * function may be used locklessly.
+ */
+static inline int hlist_nulls_unhashed_lockless(const struct hlist_nulls_node *h)
+{
+	return !READ_ONCE(h->pprev);
+}
+
 static inline int hlist_nulls_empty(const struct hlist_nulls_head *h)
 {
 	return is_a_nulls(READ_ONCE(h->first));

^ permalink raw reply	[flat|nested] 9+ messages in thread

end of thread, back to index

Thread overview: 9+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2019-11-07 19:37 [PATCH 1/2] list: add hlist_unhashed_lockless() Eric Dumazet
2019-11-07 19:37 ` [PATCH 2/2] timer: use hlist_unhashed_lockless() in timer_pending() Eric Dumazet
2019-11-08 19:27   ` Paul E. McKenney
2019-11-08 19:24 ` [PATCH 1/2] list: add hlist_unhashed_lockless() Paul E. McKenney
2019-11-08 20:17   ` Eric Dumazet
2019-11-08 23:42     ` Paul E. McKenney
2019-11-09  3:15       ` Eric Dumazet
2019-11-09 17:54         ` Paul E. McKenney
2019-11-09 18:53           ` Paul E. McKenney

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