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!!
Signed-off-by: Amol Grover <[email protected]>
---
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 6e68def66822..99c864eb6e34 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
ipmr_for_each_table() uses list_for_each_entry_rcu() for
traversing outside of an RCU read-side critical section but
under the protection of pernet_ops_rwsem. Hence add the
corresponding lockdep expression to silence the following
false-positive warning at boot:
[ 0.645292] =============================
[ 0.645294] WARNING: suspicious RCU usage
[ 0.645296] 5.5.4-stable #17 Not tainted
[ 0.645297] -----------------------------
[ 0.645299] net/ipv4/ipmr.c:136 RCU-list traversed in non-reader section!!
Signed-off-by: Amol Grover <[email protected]>
---
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 99c864eb6e34..950ffe9943da 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() || \
+ lockdep_is_held(&pernet_ops_rwsem))
static struct mr_table *ipmr_mr_table_iter(struct net *net,
struct mr_table *mrt)
--
2.24.1
On Sat, 9 May 2020 12:52:44 +0530 Amol Grover wrote:
> ipmr_for_each_table() uses list_for_each_entry_rcu() for
> traversing outside of an RCU read-side critical section but
> under the protection of pernet_ops_rwsem. Hence add the
> corresponding lockdep expression to silence the following
> false-positive warning at boot:
Thanks for the fix, the warning has been annoying me as well!
> [ 0.645292] =============================
> [ 0.645294] WARNING: suspicious RCU usage
> [ 0.645296] 5.5.4-stable #17 Not tainted
> [ 0.645297] -----------------------------
> [ 0.645299] net/ipv4/ipmr.c:136 RCU-list traversed in non-reader section!!
please provide a fuller stack trace, it would have helped the review
> Signed-off-by: Amol Grover <[email protected]>
> ---
> 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 99c864eb6e34..950ffe9943da 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() || \
> + lockdep_is_held(&pernet_ops_rwsem))
This is a strange condition, IMHO. How can we be fine with either
lock.. This is supposed to be the writer side lock, one can't have
two writer side locks..
I think what is happening is this:
ipmr_net_init() -> ipmr_rules_init() -> ipmr_new_table()
ipmr_new_table() returns an existing table if there is one, but
obviously none can exist at init. So a better fix would be:
#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))
Thoughts?
On Sat, May 09, 2020 at 02:19:38PM -0700, Jakub Kicinski wrote:
> On Sat, 9 May 2020 12:52:44 +0530 Amol Grover wrote:
> > ipmr_for_each_table() uses list_for_each_entry_rcu() for
> > traversing outside of an RCU read-side critical section but
> > under the protection of pernet_ops_rwsem. Hence add the
> > corresponding lockdep expression to silence the following
> > false-positive warning at boot:
>
> Thanks for the fix, the warning has been annoying me as well!
>
> > [ 0.645292] =============================
> > [ 0.645294] WARNING: suspicious RCU usage
> > [ 0.645296] 5.5.4-stable #17 Not tainted
> > [ 0.645297] -----------------------------
> > [ 0.645299] net/ipv4/ipmr.c:136 RCU-list traversed in non-reader section!!
>
> please provide a fuller stack trace, it would have helped the review
>
> > Signed-off-by: Amol Grover <[email protected]>
> > ---
> > 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 99c864eb6e34..950ffe9943da 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() || \
> > + lockdep_is_held(&pernet_ops_rwsem))
>
> This is a strange condition, IMHO. How can we be fine with either
> lock.. This is supposed to be the writer side lock, one can't have
> two writer side locks..
>
> I think what is happening is this:
>
> ipmr_net_init() -> ipmr_rules_init() -> ipmr_new_table()
>
> ipmr_new_table() returns an existing table if there is one, but
> obviously none can exist at init. So a better fix would be:
>
> #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))
>
(adding Stephen)
Hi Jakub,
Thank you for your suggestion about this patch.
Here is a stack trace for ipmr.c:
[ 1.515015] TCP: Hash tables configured (established 8192 bind 8192)
[ 1.516790] UDP hash table entries: 512 (order: 3, 49152 bytes, linear)
[ 1.518177] UDP-Lite hash table entries: 512 (order: 3, 49152 bytes, linear)
[ 1.519805]
[ 1.520178] =============================
[ 1.520982] WARNING: suspicious RCU usage
[ 1.521798] 5.7.0-rc2-00006-gb35af6a26b7c6f #1 Not tainted
[ 1.522910] -----------------------------
[ 1.523671] net/ipv4/ipmr.c:136 RCU-list traversed in non-reader section!!
[ 1.525218]
[ 1.525218] other info that might help us debug this:
[ 1.525218]
[ 1.526731]
[ 1.526731] rcu_scheduler_active = 2, debug_locks = 1
[ 1.528004] 1 lock held by swapper/1:
[ 1.528714] #0: c20be1d8 (pernet_ops_rwsem){+.+.}-{3:3}, at: register_pernet_subsys+0xd/0x30
[ 1.530433]
[ 1.530433] stack backtrace:
[ 1.531262] CPU: 0 PID: 1 Comm: swapper Not tainted 5.7.0-rc2-00006-gb35af6a26b7c6f #1
[ 1.532729] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.12.0-1 04/01/2014
[ 1.534305] Call Trace:
[ 1.534758] ? ipmr_get_table+0x3c/0x70
[ 1.535430] ? ipmr_new_table+0x1c/0x60
[ 1.536173] ? ipmr_net_init+0x7b/0x170
[ 1.536923] ? register_pernet_subsys+0xd/0x30
[ 1.537810] ? ops_init+0x1a0/0x1e0
[ 1.538518] ? kmem_cache_create_usercopy+0x28a/0x350
[ 1.539752] ? register_pernet_operations+0xc9/0x1c0
[ 1.540630] ? ipv4_offload_init+0x65/0x65
[ 1.541451] ? register_pernet_subsys+0x19/0x30
[ 1.542357] ? ip_mr_init+0x28/0xff
[ 1.543079] ? inet_init+0x17b/0x249
[ 1.543773] ? do_one_initcall+0xc5/0x240
[ 1.544532] ? parse_args+0x192/0x350
[ 1.545266] ? rcu_read_lock_sched_held+0x2f/0x60
[ 1.546180] ? trace_initcall_level+0x61/0x93
[ 1.547061] ? kernel_init_freeable+0x112/0x18a
[ 1.547978] ? kernel_init_freeable+0x12b/0x18a
[ 1.548974] ? rest_init+0x220/0x220
[ 1.549792] ? kernel_init+0x8/0x100
[ 1.550548] ? rest_init+0x220/0x220
[ 1.551288] ? schedule_tail_wrapper+0x6/0x8
[ 1.552136] ? rest_init+0x220/0x220
[ 1.552873] ? ret_from_fork+0x2e/0x38
ALso, there is a similar warning for ip6mr.c :
=============================
WARNING: suspicious RCU usage
5.7.0-rc4-next-20200507-syzkaller #0 Not tainted
-----------------------------
net/ipv6/ip6mr.c:124 RCU-list traversed in non-reader section!!
other info that might help us debug this:
rcu_scheduler_active = 2, debug_locks = 1
1 lock held by swapper/0/1:
#0: ffffffff8a7aae30 (pernet_ops_rwsem){+.+.}-{3:3}, at: register_pernet_subsys+0x16/0x40 net/core/net_namespace.c:1257
stack backtrace:
CPU: 0 PID: 1 Comm: swapper/0 Not tainted 5.7.0-rc4-next-20200507-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
Call Trace:
__dump_stack lib/dump_stack.c:77 [inline]
dump_stack+0x18f/0x20d lib/dump_stack.c:118
ip6mr_get_table+0x153/0x180 net/ipv6/ip6mr.c:124
ip6mr_new_table+0x1b/0x70 net/ipv6/ip6mr.c:382
ip6mr_rules_init net/ipv6/ip6mr.c:236 [inline]
ip6mr_net_init+0x133/0x3f0 net/ipv6/ip6mr.c:1310
ops_init+0xaf/0x420 net/core/net_namespace.c:151
__register_pernet_operations net/core/net_namespace.c:1140 [inline]
register_pernet_operations+0x346/0x840 net/core/net_namespace.c:1217
register_pernet_subsys+0x25/0x40 net/core/net_namespace.c:1258
ip6_mr_init+0x49/0x152 net/ipv6/ip6mr.c:1363
inet6_init+0x1d7/0x6dc net/ipv6/af_inet6.c:1037
do_one_initcall+0x10a/0x7d0 init/main.c:1159
do_initcall_level init/main.c:1232 [inline]
do_initcalls init/main.c:1248 [inline]
do_basic_setup init/main.c:1268 [inline]
kernel_init_freeable+0x501/0x5ae init/main.c:1454
kernel_init+0xd/0x1bb init/main.c:1359
ret_from_fork+0x24/0x30 arch/x86/entry/entry_64.S:351
Segment Routing with IPv6
mip6: Mobile IPv6
sit: IPv6, IPv4 and MPLS over IPv4 tunneling driver
ip6_gre: GRE over IPv6 tunneling driver
> Thoughts?
Do you think a similar fix (the one you suggested) is also applicable
in the ip6mr case.
Thank you,
Madhuparna
On Tue, 12 May 2020 10:47:05 +0530 Madhuparna Bhowmik wrote:
> > > #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() || \
> > > + lockdep_is_held(&pernet_ops_rwsem))
> >
> > This is a strange condition, IMHO. How can we be fine with either
> > lock.. This is supposed to be the writer side lock, one can't have
> > two writer side locks..
> >
> > I think what is happening is this:
> >
> > ipmr_net_init() -> ipmr_rules_init() -> ipmr_new_table()
> >
> > ipmr_new_table() returns an existing table if there is one, but
> > obviously none can exist at init. So a better fix would be:
> >
> > #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))
> >
> (adding Stephen)
>
> Hi Jakub,
>
> Thank you for your suggestion about this patch.
> Here is a stack trace for ipmr.c:
>
> [...]
Thanks!
> > Thoughts?
>
> Do you think a similar fix (the one you suggested) is also applicable
> in the ip6mr case.
Yes, looking at the code it seems ip6mr has the exact same flow for
netns init.
On Tue, May 12, 2020 at 10:47:05AM +0530, Madhuparna Bhowmik wrote:
> On Sat, May 09, 2020 at 02:19:38PM -0700, Jakub Kicinski wrote:
> > On Sat, 9 May 2020 12:52:44 +0530 Amol Grover wrote:
> > > ipmr_for_each_table() uses list_for_each_entry_rcu() for
> > > traversing outside of an RCU read-side critical section but
> > > under the protection of pernet_ops_rwsem. Hence add the
> > > corresponding lockdep expression to silence the following
> > > false-positive warning at boot:
> >
> > Thanks for the fix, the warning has been annoying me as well!
> >
> > > [ 0.645292] =============================
> > > [ 0.645294] WARNING: suspicious RCU usage
> > > [ 0.645296] 5.5.4-stable #17 Not tainted
> > > [ 0.645297] -----------------------------
> > > [ 0.645299] net/ipv4/ipmr.c:136 RCU-list traversed in non-reader section!!
> >
> > please provide a fuller stack trace, it would have helped the review
> >
> > > Signed-off-by: Amol Grover <[email protected]>
> > > ---
> > > 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 99c864eb6e34..950ffe9943da 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() || \
> > > + lockdep_is_held(&pernet_ops_rwsem))
> >
> > This is a strange condition, IMHO. How can we be fine with either
> > lock.. This is supposed to be the writer side lock, one can't have
> > two writer side locks..
> >
> > I think what is happening is this:
> >
> > ipmr_net_init() -> ipmr_rules_init() -> ipmr_new_table()
> >
> > ipmr_new_table() returns an existing table if there is one, but
> > obviously none can exist at init. So a better fix would be:
> >
> > #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))
> >
Jakub, I agree, this condition looks better (and correct) than the one I
proposed. I'll do the changes as necessary. Also, do you want me to add
the full trace to the git commit body as well? I omitted it on purpose
to not make it messy.
> (adding Stephen)
>
> Hi Jakub,
>
> Thank you for your suggestion about this patch.
> Here is a stack trace for ipmr.c:
>
> [ 1.515015] TCP: Hash tables configured (established 8192 bind 8192)
> [ 1.516790] UDP hash table entries: 512 (order: 3, 49152 bytes, linear)
> [ 1.518177] UDP-Lite hash table entries: 512 (order: 3, 49152 bytes, linear)
> [ 1.519805]
> [ 1.520178] =============================
> [ 1.520982] WARNING: suspicious RCU usage
> [ 1.521798] 5.7.0-rc2-00006-gb35af6a26b7c6f #1 Not tainted
> [ 1.522910] -----------------------------
> [ 1.523671] net/ipv4/ipmr.c:136 RCU-list traversed in non-reader section!!
> [ 1.525218]
> [ 1.525218] other info that might help us debug this:
> [ 1.525218]
> [ 1.526731]
> [ 1.526731] rcu_scheduler_active = 2, debug_locks = 1
> [ 1.528004] 1 lock held by swapper/1:
> [ 1.528714] #0: c20be1d8 (pernet_ops_rwsem){+.+.}-{3:3}, at: register_pernet_subsys+0xd/0x30
> [ 1.530433]
> [ 1.530433] stack backtrace:
> [ 1.531262] CPU: 0 PID: 1 Comm: swapper Not tainted 5.7.0-rc2-00006-gb35af6a26b7c6f #1
> [ 1.532729] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.12.0-1 04/01/2014
> [ 1.534305] Call Trace:
> [ 1.534758] ? ipmr_get_table+0x3c/0x70
> [ 1.535430] ? ipmr_new_table+0x1c/0x60
> [ 1.536173] ? ipmr_net_init+0x7b/0x170
> [ 1.536923] ? register_pernet_subsys+0xd/0x30
> [ 1.537810] ? ops_init+0x1a0/0x1e0
> [ 1.538518] ? kmem_cache_create_usercopy+0x28a/0x350
> [ 1.539752] ? register_pernet_operations+0xc9/0x1c0
> [ 1.540630] ? ipv4_offload_init+0x65/0x65
> [ 1.541451] ? register_pernet_subsys+0x19/0x30
> [ 1.542357] ? ip_mr_init+0x28/0xff
> [ 1.543079] ? inet_init+0x17b/0x249
> [ 1.543773] ? do_one_initcall+0xc5/0x240
> [ 1.544532] ? parse_args+0x192/0x350
> [ 1.545266] ? rcu_read_lock_sched_held+0x2f/0x60
> [ 1.546180] ? trace_initcall_level+0x61/0x93
> [ 1.547061] ? kernel_init_freeable+0x112/0x18a
> [ 1.547978] ? kernel_init_freeable+0x12b/0x18a
> [ 1.548974] ? rest_init+0x220/0x220
> [ 1.549792] ? kernel_init+0x8/0x100
> [ 1.550548] ? rest_init+0x220/0x220
> [ 1.551288] ? schedule_tail_wrapper+0x6/0x8
> [ 1.552136] ? rest_init+0x220/0x220
> [ 1.552873] ? ret_from_fork+0x2e/0x38
>
Thank you for the stacktrace Madhuparna.
> ALso, there is a similar warning for ip6mr.c :
>
> =============================
> WARNING: suspicious RCU usage
> 5.7.0-rc4-next-20200507-syzkaller #0 Not tainted
> -----------------------------
> net/ipv6/ip6mr.c:124 RCU-list traversed in non-reader section!!
>
> other info that might help us debug this:
>
> rcu_scheduler_active = 2, debug_locks = 1
> 1 lock held by swapper/0/1:
> #0: ffffffff8a7aae30 (pernet_ops_rwsem){+.+.}-{3:3}, at: register_pernet_subsys+0x16/0x40 net/core/net_namespace.c:1257
>
> stack backtrace:
> CPU: 0 PID: 1 Comm: swapper/0 Not tainted 5.7.0-rc4-next-20200507-syzkaller #0
> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
> Call Trace:
> __dump_stack lib/dump_stack.c:77 [inline]
> dump_stack+0x18f/0x20d lib/dump_stack.c:118
> ip6mr_get_table+0x153/0x180 net/ipv6/ip6mr.c:124
> ip6mr_new_table+0x1b/0x70 net/ipv6/ip6mr.c:382
> ip6mr_rules_init net/ipv6/ip6mr.c:236 [inline]
> ip6mr_net_init+0x133/0x3f0 net/ipv6/ip6mr.c:1310
> ops_init+0xaf/0x420 net/core/net_namespace.c:151
> __register_pernet_operations net/core/net_namespace.c:1140 [inline]
> register_pernet_operations+0x346/0x840 net/core/net_namespace.c:1217
> register_pernet_subsys+0x25/0x40 net/core/net_namespace.c:1258
> ip6_mr_init+0x49/0x152 net/ipv6/ip6mr.c:1363
> inet6_init+0x1d7/0x6dc net/ipv6/af_inet6.c:1037
> do_one_initcall+0x10a/0x7d0 init/main.c:1159
> do_initcall_level init/main.c:1232 [inline]
> do_initcalls init/main.c:1248 [inline]
> do_basic_setup init/main.c:1268 [inline]
> kernel_init_freeable+0x501/0x5ae init/main.c:1454
> kernel_init+0xd/0x1bb init/main.c:1359
> ret_from_fork+0x24/0x30 arch/x86/entry/entry_64.S:351
> Segment Routing with IPv6
> mip6: Mobile IPv6
> sit: IPv6, IPv4 and MPLS over IPv4 tunneling driver
> ip6_gre: GRE over IPv6 tunneling driver
>
> > Thoughts?
>
> Do you think a similar fix (the one you suggested) is also applicable
> in the ip6mr case.
>
> Thank you,
> Madhuparna
On Tue, 12 May 2020 22:47:10 +0530 Amol Grover wrote:
> > > This is a strange condition, IMHO. How can we be fine with either
> > > lock.. This is supposed to be the writer side lock, one can't have
> > > two writer side locks..
> > >
> > > I think what is happening is this:
> > >
> > > ipmr_net_init() -> ipmr_rules_init() -> ipmr_new_table()
> > >
> > > ipmr_new_table() returns an existing table if there is one, but
> > > obviously none can exist at init. So a better fix would be:
> > >
> > > #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))
> > >
>
> Jakub, I agree, this condition looks better (and correct) than the one I
> proposed. I'll do the changes as necessary. Also, do you want me to add
> the full trace to the git commit body as well? I omitted it on purpose
> to not make it messy.
In this case we can leave it at the depth of IPMR code + the caller, so:
[ 1.534758] ? ipmr_get_table+0x3c/0x70
[ 1.535430] ? ipmr_new_table+0x1c/0x60
[ 1.536173] ? ipmr_net_init+0x7b/0x170
[ 1.536923] ? register_pernet_subsys+0xd/0x30
This makes it clear that the problem happens at net namespace init.
Thanks!
On Tue, May 12, 2020 at 09:32:31AM -0700, Jakub Kicinski wrote:
> On Tue, 12 May 2020 10:47:05 +0530 Madhuparna Bhowmik wrote:
> > > > #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() || \
> > > > + lockdep_is_held(&pernet_ops_rwsem))
> > >
> > > This is a strange condition, IMHO. How can we be fine with either
> > > lock.. This is supposed to be the writer side lock, one can't have
> > > two writer side locks..
> > >
> > > I think what is happening is this:
> > >
> > > ipmr_net_init() -> ipmr_rules_init() -> ipmr_new_table()
> > >
> > > ipmr_new_table() returns an existing table if there is one, but
> > > obviously none can exist at init. So a better fix would be:
> > >
> > > #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))
> > >
> > (adding Stephen)
> >
> > Hi Jakub,
> >
> > Thank you for your suggestion about this patch.
> > Here is a stack trace for ipmr.c:
> >
> > [...]
>
> Thanks!
>
> > > Thoughts?
> >
> > Do you think a similar fix (the one you suggested) is also applicable
> > in the ip6mr case.
>
> Yes, looking at the code it seems ip6mr has the exact same flow for
> netns init.
Alright, thanks a lot.
I will send a patch for ip6mr.c soon.
Thank you,
Madhuparna
Hi all,
On Tue, 12 May 2020 10:47:05 +0530 Madhuparna Bhowmik <[email protected]> wrote:
> >
> > I think what is happening is this:
> >
> > ipmr_net_init() -> ipmr_rules_init() -> ipmr_new_table()
> >
> > ipmr_new_table() returns an existing table if there is one, but
> > obviously none can exist at init. So a better fix would be:
> >
> > #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))
> >
> (adding Stephen)
I have changed the patch in my fixes tree to this.
--
Cheers,
Stephen Rothwell