| Message ID | 20200420150133.2586-1-ap420073@gmail.com |
|---|---|
| State | Accepted |
| Delegated to: | David Miller |
| Headers | show |
| Series | [net,v3] team: fix hang in team_mode_get() | expand |
Mon, Apr 20, 2020 at 05:01:33PM 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> Reviewed-by: Jiri Pirko <jiri@mellanox.com>
From: Taehee Yoo <ap420073@gmail.com> Date: Mon, 20 Apr 2020 15:01:33 +0000 > 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> Applied and queued up for -stable, thanks.
diff --git a/drivers/net/team/team.c b/drivers/net/team/team.c index 4004f98e50d9..04845a4017f9 100644 --- a/drivers/net/team/team.c +++ b/drivers/net/team/team.c @@ -468,6 +468,9 @@ static const struct team_mode *team_mode_get(const char *kind) 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_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> --- v2 -> v3: - Remove unrelated change v1 -> v2: - Remove unnecessary #if statement and 'put' variable drivers/net/team/team.c | 4 ++++ 1 file changed, 4 insertions(+)