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author | Taehee Yoo <ap420073@gmail.com> | 2020-04-20 17:01:33 +0200 |
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committer | David S. Miller <davem@davemloft.net> | 2020-04-20 22:03:44 +0200 |
commit | 1c30fbc76b8f0c07c92a8ca4cd7c456612e17eb5 (patch) | |
tree | 3c35f518e31d3bb6b2a423204acc54f9624e27ca /drivers/net/team | |
parent | Merge branch 'mptcp-fix-races-on-accept' (diff) | |
download | linux-1c30fbc76b8f0c07c92a8ca4cd7c456612e17eb5.tar.xz linux-1c30fbc76b8f0c07c92a8ca4cd7c456612e17eb5.zip |
team: fix hang in team_mode_get()
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>
Diffstat (limited to 'drivers/net/team')
-rw-r--r-- | drivers/net/team/team.c | 4 |
1 files changed, 4 insertions, 0 deletions
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; } |