| Message ID | 20200420131145.20146-1-ap420073@gmail.com |
|---|---|
| State | Changes Requested |
| Delegated to: | David Miller |
| Headers | show |
| Series | [net,v2] team: fix hang in team_mode_get() | expand |
Mon, Apr 20, 2020 at 03:11:45PM CEST, ap420073@gmail.com wrote: [...] >diff --git a/drivers/net/team/team.c b/drivers/net/team/team.c >index 4004f98e50d9..4f1ccbafb961 100644 >--- a/drivers/net/team/team.c >+++ b/drivers/net/team/team.c >@@ -465,8 +465,11 @@ 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; Remove this unrelated move from the patch. >+ >+ if (!try_module_get(THIS_MODULE)) >+ return NULL; > > spin_lock(&mode_list_lock); > mitem = __find_mode(kind); >@@ -483,6 +486,7 @@ static const struct team_mode *team_mode_get(const char *kind) > } > > spin_unlock(&mode_list_lock); >+ module_put(THIS_MODULE); > return mode; > } > >-- >2.17.1 >
On Mon, 20 Apr 2020 at 23:35, Jiri Pirko <jiri@resnulli.us> wrote: > Hi Jiri, Thank you for the review. > Mon, Apr 20, 2020 at 03:11:45PM CEST, ap420073@gmail.com wrote: > > [...] > > > >diff --git a/drivers/net/team/team.c b/drivers/net/team/team.c > >index 4004f98e50d9..4f1ccbafb961 100644 > >--- a/drivers/net/team/team.c > >+++ b/drivers/net/team/team.c > >@@ -465,8 +465,11 @@ 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; > > Remove this unrelated move from the patch. > Okay, I will send a v3 patch. Thanks a lot! Taehee Yoo
diff --git a/drivers/net/team/team.c b/drivers/net/team/team.c index 4004f98e50d9..4f1ccbafb961 100644 --- a/drivers/net/team/team.c +++ b/drivers/net/team/team.c @@ -465,8 +465,11 @@ 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; + + if (!try_module_get(THIS_MODULE)) + return NULL; spin_lock(&mode_list_lock); mitem = __find_mode(kind); @@ -483,6 +486,7 @@ static const struct team_mode *team_mode_get(const char *kind) } spin_unlock(&mode_list_lock); + module_put(THIS_MODULE); return mode; }
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> --- v1 -> v2: - Remove unnecessary #if statement and 'put' variable drivers/net/team/team.c | 6 +++++- 1 file changed, 5 insertions(+), 1 deletion(-)