From: Taehee Yoo ap420073@gmail.com
[ Upstream commit 1c30fbc76b8f0c07c92a8ca4cd7c456612e17eb5 ]
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 Reviewed-by: Jiri Pirko jiri@mellanox.com Signed-off-by: David S. Miller davem@davemloft.net Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- drivers/net/team/team.c | 4 ++++ 1 file changed, 4 insertions(+)
--- a/drivers/net/team/team.c +++ b/drivers/net/team/team.c @@ -468,6 +468,9 @@ static const struct team_mode *team_mode struct team_mode_item *mitem; const struct team_mode *mode = NULL;
+ if (!try_module_get(THIS_MODULE)) + return NULL; + spin_lock(&mode_list_lock); mitem = __find_mode(kind); if (!mitem) { @@ -483,6 +486,7 @@ static const struct team_mode *team_mode }
spin_unlock(&mode_list_lock); + module_put(THIS_MODULE); return mode; }