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1c30fbc76b
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:
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| .. | ||
| appletalk | ||
| arcnet | ||
| bonding | ||
| caif | ||
| can | ||
| dsa | ||
| ethernet | ||
| fddi | ||
| fjes | ||
| hamradio | ||
| hippi | ||
| hyperv | ||
| ieee802154 | ||
| ipa | ||
| ipvlan | ||
| netdevsim | ||
| phy | ||
| plip | ||
| ppp | ||
| slip | ||
| team | ||
| usb | ||
| vmxnet3 | ||
| wan | ||
| wimax | ||
| wireguard | ||
| wireless | ||
| xen-netback | ||
| bareudp.c | ||
| dummy.c | ||
| eql.c | ||
| geneve.c | ||
| gtp.c | ||
| ifb.c | ||
| Kconfig | ||
| LICENSE.SRC | ||
| loopback.c | ||
| macsec.c | ||
| macvlan.c | ||
| macvtap.c | ||
| Makefile | ||
| mdio.c | ||
| mii.c | ||
| net_failover.c | ||
| netconsole.c | ||
| nlmon.c | ||
| ntb_netdev.c | ||
| rionet.c | ||
| sb1000.c | ||
| Space.c | ||
| sungem_phy.c | ||
| tap.c | ||
| thunderbolt.c | ||
| tun.c | ||
| veth.c | ||
| virtio_net.c | ||
| vrf.c | ||
| vsockmon.c | ||
| vxlan.c | ||
| xen-netfront.c | ||