* [PATCH net] team: fix hang in team_mode_get()
@ 2020-04-18 16:17 Taehee Yoo
2020-04-20 10:21 ` Jiri Pirko
0 siblings, 1 reply; 3+ messages in thread
From: Taehee Yoo @ 2020-04-18 16:17 UTC (permalink / raw)
To: davem, kuba, jiri, netdev; +Cc: ap420073
When team mode is changed or set, the team_mode_get() is called to check
whether the mode module is inserted or not. If the mode module is not
inserted, it calls the request_module().
In the request_module(), it creates a child process, which is
the "modprobe" process and waits for the done of the child process.
At this point, the following locks were used.
down_read(&cb_lock()); by genl_rcv()
genl_lock(); by genl_rcv_msc()
rtnl_lock(); by team_nl_cmd_options_set()
mutex_lock(&team->lock); by team_nl_team_get()
Concurrently, the team module could be removed by rmmod or "modprobe -r"
The __exit function of team module is team_module_exit(), which calls
team_nl_fini() and it tries to acquire following locks.
down_write(&cb_lock);
genl_lock();
Because of the genl_lock() and cb_lock, this process can't be finished
earlier than request_module() routine.
The problem secenario.
CPU0 CPU1
team_mode_get
request_module()
modprobe -r team_mode_roundrobin
team <--(B)
modprobe team <--(A)
team_mode_roundrobin
By request_module(), the "modprobe team_mode_roundrobin" command
will be executed. At this point, the modprobe process will decide
that the team module should be inserted before team_mode_roundrobin.
Because the team module is being removed.
By the module infrastructure, the same module insert/remove operations
can't be executed concurrently.
So, (A) waits for (B) but (B) also waits for (A) because of locks.
So that the hang occurs at this point.
Test commands:
while :
do
teamd -d &
killall teamd &
modprobe -rv team_mode_roundrobin &
done
The approach of this patch is to hold the reference count of the team
module if the team module is compiled as a module. If the reference count
of the team module is not zero while request_module() is being called,
the team module will not be removed at that moment.
So that the above scenario could not occur.
Fixes: 3d249d4ca7d0 ("net: introduce ethernet teaming device")
Signed-off-by: Taehee Yoo <ap420073@gmail.com>
---
drivers/net/team/team.c | 10 +++++++++-
1 file changed, 9 insertions(+), 1 deletion(-)
diff --git a/drivers/net/team/team.c b/drivers/net/team/team.c
index 4004f98e50d9..21702bc23705 100644
--- a/drivers/net/team/team.c
+++ b/drivers/net/team/team.c
@@ -465,9 +465,15 @@ EXPORT_SYMBOL(team_mode_unregister);
static const struct team_mode *team_mode_get(const char *kind)
{
- struct team_mode_item *mitem;
const struct team_mode *mode = NULL;
+ struct team_mode_item *mitem;
+ bool put = false;
+#if IS_MODULE(CONFIG_NET_TEAM)
+ if (!try_module_get(THIS_MODULE))
+ return NULL;
+ put = true;
+#endif
spin_lock(&mode_list_lock);
mitem = __find_mode(kind);
if (!mitem) {
@@ -483,6 +489,8 @@ static const struct team_mode *team_mode_get(const char *kind)
}
spin_unlock(&mode_list_lock);
+ if (put)
+ module_put(THIS_MODULE);
return mode;
}
--
2.17.1
^ permalink raw reply related [flat|nested] 3+ messages in thread
* Re: [PATCH net] team: fix hang in team_mode_get()
2020-04-18 16:17 [PATCH net] team: fix hang in team_mode_get() Taehee Yoo
@ 2020-04-20 10:21 ` Jiri Pirko
2020-04-20 11:18 ` Taehee Yoo
0 siblings, 1 reply; 3+ messages in thread
From: Jiri Pirko @ 2020-04-20 10:21 UTC (permalink / raw)
To: Taehee Yoo; +Cc: davem, kuba, netdev
Sat, Apr 18, 2020 at 06:17:29PM CEST, ap420073@gmail.com wrote:
>When team mode is changed or set, the team_mode_get() is called to check
>whether the mode module is inserted or not. If the mode module is not
>inserted, it calls the request_module().
>In the request_module(), it creates a child process, which is
>the "modprobe" process and waits for the done of the child process.
>At this point, the following locks were used.
>down_read(&cb_lock()); by genl_rcv()
> genl_lock(); by genl_rcv_msc()
> rtnl_lock(); by team_nl_cmd_options_set()
> mutex_lock(&team->lock); by team_nl_team_get()
>
>Concurrently, the team module could be removed by rmmod or "modprobe -r"
>The __exit function of team module is team_module_exit(), which calls
>team_nl_fini() and it tries to acquire following locks.
>down_write(&cb_lock);
> genl_lock();
>Because of the genl_lock() and cb_lock, this process can't be finished
>earlier than request_module() routine.
>
>The problem secenario.
>CPU0 CPU1
>team_mode_get
> request_module()
> modprobe -r team_mode_roundrobin
> team <--(B)
> modprobe team <--(A)
> team_mode_roundrobin
>
>By request_module(), the "modprobe team_mode_roundrobin" command
>will be executed. At this point, the modprobe process will decide
>that the team module should be inserted before team_mode_roundrobin.
>Because the team module is being removed.
>
>By the module infrastructure, the same module insert/remove operations
>can't be executed concurrently.
>So, (A) waits for (B) but (B) also waits for (A) because of locks.
>So that the hang occurs at this point.
>
>Test commands:
> while :
> do
> teamd -d &
> killall teamd &
> modprobe -rv team_mode_roundrobin &
> done
>
>The approach of this patch is to hold the reference count of the team
>module if the team module is compiled as a module. If the reference count
>of the team module is not zero while request_module() is being called,
>the team module will not be removed at that moment.
>So that the above scenario could not occur.
>
>Fixes: 3d249d4ca7d0 ("net: introduce ethernet teaming device")
>Signed-off-by: Taehee Yoo <ap420073@gmail.com>
>---
> drivers/net/team/team.c | 10 +++++++++-
> 1 file changed, 9 insertions(+), 1 deletion(-)
>
>diff --git a/drivers/net/team/team.c b/drivers/net/team/team.c
>index 4004f98e50d9..21702bc23705 100644
>--- a/drivers/net/team/team.c
>+++ b/drivers/net/team/team.c
>@@ -465,9 +465,15 @@ EXPORT_SYMBOL(team_mode_unregister);
>
> static const struct team_mode *team_mode_get(const char *kind)
> {
>- struct team_mode_item *mitem;
> const struct team_mode *mode = NULL;
>+ struct team_mode_item *mitem;
>+ bool put = false;
>
>+#if IS_MODULE(CONFIG_NET_TEAM)
>+ if (!try_module_get(THIS_MODULE))
Can't you call this in case this is not a module? Wouldn't THIS_MODULE
be NULL then? try_module_get() handles that correctly.
>+ return NULL;
>+ put = true;
>+#endif
> spin_lock(&mode_list_lock);
> mitem = __find_mode(kind);
> if (!mitem) {
>@@ -483,6 +489,8 @@ static const struct team_mode *team_mode_get(const char *kind)
> }
>
> spin_unlock(&mode_list_lock);
>+ if (put)
>+ module_put(THIS_MODULE);
Can't you just put this under the same "if IS_MODULE" statement and
avoid the "put" variable? Or in case the statement is not needed, just
do plain module_put call.
Otherwise, the patch looks fine.
> return mode;
> }
>
>--
>2.17.1
>
^ permalink raw reply [flat|nested] 3+ messages in thread
* Re: [PATCH net] team: fix hang in team_mode_get()
2020-04-20 10:21 ` Jiri Pirko
@ 2020-04-20 11:18 ` Taehee Yoo
0 siblings, 0 replies; 3+ messages in thread
From: Taehee Yoo @ 2020-04-20 11:18 UTC (permalink / raw)
To: Jiri Pirko; +Cc: David Miller, Jakub Kicinski, Netdev
On Mon, 20 Apr 2020 at 19:21, Jiri Pirko <jiri@resnulli.us> wrote:
>
Hi Jiri,
Thank you for your review!
> Sat, Apr 18, 2020 at 06:17:29PM CEST, ap420073@gmail.com wrote:
> >When team mode is changed or set, the team_mode_get() is called to check
> >whether the mode module is inserted or not. If the mode module is not
> >inserted, it calls the request_module().
> >In the request_module(), it creates a child process, which is
> >the "modprobe" process and waits for the done of the child process.
> >At this point, the following locks were used.
> >down_read(&cb_lock()); by genl_rcv()
> > genl_lock(); by genl_rcv_msc()
> > rtnl_lock(); by team_nl_cmd_options_set()
> > mutex_lock(&team->lock); by team_nl_team_get()
> >
> >Concurrently, the team module could be removed by rmmod or "modprobe -r"
> >The __exit function of team module is team_module_exit(), which calls
> >team_nl_fini() and it tries to acquire following locks.
> >down_write(&cb_lock);
> > genl_lock();
> >Because of the genl_lock() and cb_lock, this process can't be finished
> >earlier than request_module() routine.
> >
> >The problem secenario.
> >CPU0 CPU1
> >team_mode_get
> > request_module()
> > modprobe -r team_mode_roundrobin
> > team <--(B)
> > modprobe team <--(A)
> > team_mode_roundrobin
> >
> >By request_module(), the "modprobe team_mode_roundrobin" command
> >will be executed. At this point, the modprobe process will decide
> >that the team module should be inserted before team_mode_roundrobin.
> >Because the team module is being removed.
> >
> >By the module infrastructure, the same module insert/remove operations
> >can't be executed concurrently.
> >So, (A) waits for (B) but (B) also waits for (A) because of locks.
> >So that the hang occurs at this point.
> >
> >Test commands:
> > while :
> > do
> > teamd -d &
> > killall teamd &
> > modprobe -rv team_mode_roundrobin &
> > done
> >
> >The approach of this patch is to hold the reference count of the team
> >module if the team module is compiled as a module. If the reference count
> >of the team module is not zero while request_module() is being called,
> >the team module will not be removed at that moment.
> >So that the above scenario could not occur.
> >
> >Fixes: 3d249d4ca7d0 ("net: introduce ethernet teaming device")
> >Signed-off-by: Taehee Yoo <ap420073@gmail.com>
> >---
> > drivers/net/team/team.c | 10 +++++++++-
> > 1 file changed, 9 insertions(+), 1 deletion(-)
> >
> >diff --git a/drivers/net/team/team.c b/drivers/net/team/team.c
> >index 4004f98e50d9..21702bc23705 100644
> >--- a/drivers/net/team/team.c
> >+++ b/drivers/net/team/team.c
> >@@ -465,9 +465,15 @@ EXPORT_SYMBOL(team_mode_unregister);
> >
> > static const struct team_mode *team_mode_get(const char *kind)
> > {
> >- struct team_mode_item *mitem;
> > const struct team_mode *mode = NULL;
> >+ struct team_mode_item *mitem;
> >+ bool put = false;
> >
> >+#if IS_MODULE(CONFIG_NET_TEAM)
> >+ if (!try_module_get(THIS_MODULE))
>
> Can't you call this in case this is not a module? Wouldn't THIS_MODULE
> be NULL then? try_module_get() handles that correctly.
>
>
> >+ return NULL;
> >+ put = true;
> >+#endif
> > spin_lock(&mode_list_lock);
> > mitem = __find_mode(kind);
> > if (!mitem) {
> >@@ -483,6 +489,8 @@ static const struct team_mode *team_mode_get(const char *kind)
> > }
> >
> > spin_unlock(&mode_list_lock);
> >+ if (put)
> >+ module_put(THIS_MODULE);
>
> Can't you just put this under the same "if IS_MODULE" statement and
> avoid the "put" variable? Or in case the statement is not needed, just
> do plain module_put call.
>
> Otherwise, the patch looks fine.
>
You're right, If the team is not a module, THIS_MODULE will be null.
try_module_get() and module_put() deal with NULL well.
So, I will send a v2 patch that will remove the #if statement and
the put variable.
Thanks a lot!
Taehee Yoo
^ permalink raw reply [flat|nested] 3+ messages in thread
end of thread, other threads:[~2020-04-20 11:18 UTC | newest]
Thread overview: 3+ messages (download: mbox.gz follow: Atom feed
-- links below jump to the message on this page --
2020-04-18 16:17 [PATCH net] team: fix hang in team_mode_get() Taehee Yoo
2020-04-20 10:21 ` Jiri Pirko
2020-04-20 11:18 ` Taehee Yoo
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).