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* [Linux-kernel-mentees] [PATCH net v2 1/2] ipmr: Fix RCU list debugging warning
@ 2020-05-14 18:01 Amol Grover
  2020-05-14 18:01 ` [Linux-kernel-mentees] [PATCH net v2 2/2] ipmr: Add lockdep expression to ipmr_for_each_table macro Amol Grover
  2020-05-15  1:01 ` [Linux-kernel-mentees] [PATCH net v2 1/2] ipmr: Fix RCU list debugging warning David Miller
  0 siblings, 2 replies; 4+ messages in thread
From: Amol Grover @ 2020-05-14 18:01 UTC (permalink / raw)
  To: David S . Miller, Alexey Kuznetsov, Hideaki YOSHIFUJI,
	Jakub Kicinski, Patrick McHardy, Stephen Rothwell, Qian Cai
  Cc: Paul E . McKenney, netdev, linux-kernel, Madhuparna Bhowmik,
	Joel Fernandes, linux-kernel-mentees

ipmr_for_each_table() macro uses list_for_each_entry_rcu()
for traversing outside of an RCU read side critical section
but under the protection of rtnl_mutex. Hence, add the
corresponding lockdep expression to silence the following
false-positive warning at boot:

[    4.319347] =============================
[    4.319349] WARNING: suspicious RCU usage
[    4.319351] 5.5.4-stable #17 Tainted: G            E
[    4.319352] -----------------------------
[    4.319354] net/ipv4/ipmr.c:1757 RCU-list traversed in non-reader section!!

Fixes: f0ad0860d01e ("ipv4: ipmr: support multiple tables")
Signed-off-by: Amol Grover <frextrite@gmail.com>
---
v2:
- Add appropriate Fixes tag

 net/ipv4/ipmr.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/net/ipv4/ipmr.c b/net/ipv4/ipmr.c
index 9cf83cc85e4a..4897f7420c8f 100644
--- a/net/ipv4/ipmr.c
+++ b/net/ipv4/ipmr.c
@@ -110,7 +110,8 @@ static void ipmr_expire_process(struct timer_list *t);
 
 #ifdef CONFIG_IP_MROUTE_MULTIPLE_TABLES
 #define ipmr_for_each_table(mrt, net) \
-	list_for_each_entry_rcu(mrt, &net->ipv4.mr_tables, list)
+	list_for_each_entry_rcu(mrt, &net->ipv4.mr_tables, list, \
+				lockdep_rtnl_is_held())
 
 static struct mr_table *ipmr_mr_table_iter(struct net *net,
 					   struct mr_table *mrt)
-- 
2.24.1

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^ permalink raw reply	[flat|nested] 4+ messages in thread

* [Linux-kernel-mentees] [PATCH net v2 2/2] ipmr: Add lockdep expression to ipmr_for_each_table macro
  2020-05-14 18:01 [Linux-kernel-mentees] [PATCH net v2 1/2] ipmr: Fix RCU list debugging warning Amol Grover
@ 2020-05-14 18:01 ` Amol Grover
  2020-05-15  1:01   ` David Miller
  2020-05-15  1:01 ` [Linux-kernel-mentees] [PATCH net v2 1/2] ipmr: Fix RCU list debugging warning David Miller
  1 sibling, 1 reply; 4+ messages in thread
From: Amol Grover @ 2020-05-14 18:01 UTC (permalink / raw)
  To: David S . Miller, Alexey Kuznetsov, Hideaki YOSHIFUJI,
	Jakub Kicinski, Patrick McHardy, Stephen Rothwell, Qian Cai
  Cc: Paul E . McKenney, netdev, syzbot+1519f497f2f9f08183c6,
	linux-kernel, Madhuparna Bhowmik, Joel Fernandes,
	linux-kernel-mentees

During the initialization process, ipmr_new_table() is called
to create new tables which in turn calls ipmr_get_table() which
traverses net->ipv4.mr_tables without holding the writer lock.
However, this is safe to do so as no tables exist at this time.
Hence add a suitable lockdep expression to silence the following
false-positive warning:

=============================
WARNING: suspicious RCU usage
5.7.0-rc3-next-20200428-syzkaller #0 Not tainted
-----------------------------
net/ipv4/ipmr.c:136 RCU-list traversed in non-reader section!!

ipmr_get_table+0x130/0x160 net/ipv4/ipmr.c:136
ipmr_new_table net/ipv4/ipmr.c:403 [inline]
ipmr_rules_init net/ipv4/ipmr.c:248 [inline]
ipmr_net_init+0x133/0x430 net/ipv4/ipmr.c:3089

Fixes: f0ad0860d01e ("ipv4: ipmr: support multiple tables")
Reported-by: syzbot+1519f497f2f9f08183c6@syzkaller.appspotmail.com
Suggested-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: Amol Grover <frextrite@gmail.com>
---
v2:
- Change the lockdep expression to check for list emptiness at init
- Add Fixes tag
- Add Reported-by tag for syzbot report

 net/ipv4/ipmr.c | 7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)

diff --git a/net/ipv4/ipmr.c b/net/ipv4/ipmr.c
index 4897f7420c8f..5c218db2dede 100644
--- a/net/ipv4/ipmr.c
+++ b/net/ipv4/ipmr.c
@@ -109,9 +109,10 @@ static void mroute_clean_tables(struct mr_table *mrt, int flags);
 static void ipmr_expire_process(struct timer_list *t);
 
 #ifdef CONFIG_IP_MROUTE_MULTIPLE_TABLES
-#define ipmr_for_each_table(mrt, net) \
-	list_for_each_entry_rcu(mrt, &net->ipv4.mr_tables, list, \
-				lockdep_rtnl_is_held())
+#define ipmr_for_each_table(mrt, net)					\
+	list_for_each_entry_rcu(mrt, &net->ipv4.mr_tables, list,	\
+				lockdep_rtnl_is_held() ||		\
+				list_empty(&net->ipv4.mr_tables))
 
 static struct mr_table *ipmr_mr_table_iter(struct net *net,
 					   struct mr_table *mrt)
-- 
2.24.1

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Linux-kernel-mentees@lists.linuxfoundation.org
https://lists.linuxfoundation.org/mailman/listinfo/linux-kernel-mentees

^ permalink raw reply	[flat|nested] 4+ messages in thread

* Re: [Linux-kernel-mentees] [PATCH net v2 1/2] ipmr: Fix RCU list debugging warning
  2020-05-14 18:01 [Linux-kernel-mentees] [PATCH net v2 1/2] ipmr: Fix RCU list debugging warning Amol Grover
  2020-05-14 18:01 ` [Linux-kernel-mentees] [PATCH net v2 2/2] ipmr: Add lockdep expression to ipmr_for_each_table macro Amol Grover
@ 2020-05-15  1:01 ` David Miller
  1 sibling, 0 replies; 4+ messages in thread
From: David Miller @ 2020-05-15  1:01 UTC (permalink / raw)
  To: frextrite
  Cc: sfr, paulmck, yoshfuji, netdev, linux-kernel,
	madhuparnabhowmik10, cai, kuba, joel, kuznet,
	linux-kernel-mentees, kaber

From: Amol Grover <frextrite@gmail.com>
Date: Thu, 14 May 2020 23:31:02 +0530

> ipmr_for_each_table() macro uses list_for_each_entry_rcu()
> for traversing outside of an RCU read side critical section
> but under the protection of rtnl_mutex. Hence, add the
> corresponding lockdep expression to silence the following
> false-positive warning at boot:
> 
> [    4.319347] =============================
> [    4.319349] WARNING: suspicious RCU usage
> [    4.319351] 5.5.4-stable #17 Tainted: G            E
> [    4.319352] -----------------------------
> [    4.319354] net/ipv4/ipmr.c:1757 RCU-list traversed in non-reader section!!
> 
> Fixes: f0ad0860d01e ("ipv4: ipmr: support multiple tables")
> Signed-off-by: Amol Grover <frextrite@gmail.com>

Applied.
_______________________________________________
Linux-kernel-mentees mailing list
Linux-kernel-mentees@lists.linuxfoundation.org
https://lists.linuxfoundation.org/mailman/listinfo/linux-kernel-mentees

^ permalink raw reply	[flat|nested] 4+ messages in thread

* Re: [Linux-kernel-mentees] [PATCH net v2 2/2] ipmr: Add lockdep expression to ipmr_for_each_table macro
  2020-05-14 18:01 ` [Linux-kernel-mentees] [PATCH net v2 2/2] ipmr: Add lockdep expression to ipmr_for_each_table macro Amol Grover
@ 2020-05-15  1:01   ` David Miller
  0 siblings, 0 replies; 4+ messages in thread
From: David Miller @ 2020-05-15  1:01 UTC (permalink / raw)
  To: frextrite
  Cc: sfr, paulmck, syzbot+1519f497f2f9f08183c6, yoshfuji, netdev,
	linux-kernel, madhuparnabhowmik10, cai, kuba, joel, kuznet,
	linux-kernel-mentees, kaber

From: Amol Grover <frextrite@gmail.com>
Date: Thu, 14 May 2020 23:31:03 +0530

> During the initialization process, ipmr_new_table() is called
> to create new tables which in turn calls ipmr_get_table() which
> traverses net->ipv4.mr_tables without holding the writer lock.
> However, this is safe to do so as no tables exist at this time.
> Hence add a suitable lockdep expression to silence the following
> false-positive warning:
> 
> =============================
> WARNING: suspicious RCU usage
> 5.7.0-rc3-next-20200428-syzkaller #0 Not tainted
> -----------------------------
> net/ipv4/ipmr.c:136 RCU-list traversed in non-reader section!!
> 
> ipmr_get_table+0x130/0x160 net/ipv4/ipmr.c:136
> ipmr_new_table net/ipv4/ipmr.c:403 [inline]
> ipmr_rules_init net/ipv4/ipmr.c:248 [inline]
> ipmr_net_init+0x133/0x430 net/ipv4/ipmr.c:3089
> 
> Fixes: f0ad0860d01e ("ipv4: ipmr: support multiple tables")
> Reported-by: syzbot+1519f497f2f9f08183c6@syzkaller.appspotmail.com
> Suggested-by: Jakub Kicinski <kuba@kernel.org>
> Signed-off-by: Amol Grover <frextrite@gmail.com>

Applied.
_______________________________________________
Linux-kernel-mentees mailing list
Linux-kernel-mentees@lists.linuxfoundation.org
https://lists.linuxfoundation.org/mailman/listinfo/linux-kernel-mentees

^ permalink raw reply	[flat|nested] 4+ messages in thread

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-- links below jump to the message on this page --
2020-05-14 18:01 [Linux-kernel-mentees] [PATCH net v2 1/2] ipmr: Fix RCU list debugging warning Amol Grover
2020-05-14 18:01 ` [Linux-kernel-mentees] [PATCH net v2 2/2] ipmr: Add lockdep expression to ipmr_for_each_table macro Amol Grover
2020-05-15  1:01   ` David Miller
2020-05-15  1:01 ` [Linux-kernel-mentees] [PATCH net v2 1/2] ipmr: Fix RCU list debugging warning David Miller

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