Skip to content

Commit

Permalink
hv_netvsc: fix schedule in RCU context
Browse files Browse the repository at this point in the history
When netvsc device is removed it can call reschedule in RCU context.
This happens because canceling the subchannel setup work could (in theory)
cause a reschedule when manipulating the timer.

To reproduce, run with lockdep enabled kernel and unbind
a network device from hv_netvsc (via sysfs).

[  160.682011] WARNING: suspicious RCU usage
[  160.707466] 4.19.0-rc3-uio+ #2 Not tainted
[  160.709937] -----------------------------
[  160.712352] ./include/linux/rcupdate.h:302 Illegal context switch in RCU read-side critical section!
[  160.723691]
[  160.723691] other info that might help us debug this:
[  160.723691]
[  160.730955]
[  160.730955] rcu_scheduler_active = 2, debug_locks = 1
[  160.762813] 5 locks held by rebind-eth.sh/1812:
[  160.766851]  #0: 000000008befa37a (sb_writers#6){.+.+}, at: vfs_write+0x184/0x1b0
[  160.773416]  #1: 00000000b097f236 (&of->mutex){+.+.}, at: kernfs_fop_write+0xe2/0x1a0
[  160.783766]  #2: 0000000041ee6889 (kn->count#3){++++}, at: kernfs_fop_write+0xeb/0x1a0
[  160.787465]  #3: 0000000056d92a74 (&dev->mutex){....}, at: device_release_driver_internal+0x39/0x250
[  160.816987]  #4: 0000000030f6031e (rcu_read_lock){....}, at: netvsc_remove+0x1e/0x250 [hv_netvsc]
[  160.828629]
[  160.828629] stack backtrace:
[  160.831966] CPU: 1 PID: 1812 Comm: rebind-eth.sh Not tainted 4.19.0-rc3-uio+ #2
[  160.832952] Hardware name: Microsoft Corporation Virtual Machine/Virtual Machine, BIOS Hyper-V UEFI Release v1.0 11/26/2012
[  160.832952] Call Trace:
[  160.832952]  dump_stack+0x85/0xcb
[  160.832952]  ___might_sleep+0x1a3/0x240
[  160.832952]  __flush_work+0x57/0x2e0
[  160.832952]  ? __mutex_lock+0x83/0x990
[  160.832952]  ? __kernfs_remove+0x24f/0x2e0
[  160.832952]  ? __kernfs_remove+0x1b2/0x2e0
[  160.832952]  ? mark_held_locks+0x50/0x80
[  160.832952]  ? get_work_pool+0x90/0x90
[  160.832952]  __cancel_work_timer+0x13c/0x1e0
[  160.832952]  ? netvsc_remove+0x1e/0x250 [hv_netvsc]
[  160.832952]  ? __lock_is_held+0x55/0x90
[  160.832952]  netvsc_remove+0x9a/0x250 [hv_netvsc]
[  160.832952]  vmbus_remove+0x26/0x30
[  160.832952]  device_release_driver_internal+0x18a/0x250
[  160.832952]  unbind_store+0xb4/0x180
[  160.832952]  kernfs_fop_write+0x113/0x1a0
[  160.832952]  __vfs_write+0x36/0x1a0
[  160.832952]  ? rcu_read_lock_sched_held+0x6b/0x80
[  160.832952]  ? rcu_sync_lockdep_assert+0x2e/0x60
[  160.832952]  ? __sb_start_write+0x141/0x1a0
[  160.832952]  ? vfs_write+0x184/0x1b0
[  160.832952]  vfs_write+0xbe/0x1b0
[  160.832952]  ksys_write+0x55/0xc0
[  160.832952]  do_syscall_64+0x60/0x1b0
[  160.832952]  entry_SYSCALL_64_after_hwframe+0x49/0xbe
[  160.832952] RIP: 0033:0x7fe48f4c8154

Resolve this by getting RTNL earlier. This is safe because the subchannel
work queue does trylock on RTNL and will detect the race.

Fixes: 7b2ee50 ("hv_netvsc: common detach logic")
Signed-off-by: Stephen Hemminger <[email protected]>
Reviewed-by: Haiyang Zhang <[email protected]>
Signed-off-by: David S. Miller <[email protected]>
  • Loading branch information
shemminger authored and davem330 committed Sep 13, 2018
1 parent f5b9bac commit 018349d
Showing 1 changed file with 3 additions and 6 deletions.
9 changes: 3 additions & 6 deletions drivers/net/hyperv/netvsc_drv.c
Original file line number Diff line number Diff line change
Expand Up @@ -2272,17 +2272,15 @@ static int netvsc_remove(struct hv_device *dev)

cancel_delayed_work_sync(&ndev_ctx->dwork);

rcu_read_lock();
nvdev = rcu_dereference(ndev_ctx->nvdev);

if (nvdev)
rtnl_lock();
nvdev = rtnl_dereference(ndev_ctx->nvdev);
if (nvdev)
cancel_work_sync(&nvdev->subchan_work);

/*
* Call to the vsc driver to let it know that the device is being
* removed. Also blocks mtu and channel changes.
*/
rtnl_lock();
vf_netdev = rtnl_dereference(ndev_ctx->vf_netdev);
if (vf_netdev)
netvsc_unregister_vf(vf_netdev);
Expand All @@ -2294,7 +2292,6 @@ static int netvsc_remove(struct hv_device *dev)
list_del(&ndev_ctx->list);

rtnl_unlock();
rcu_read_unlock();

hv_set_drvdata(dev, NULL);

Expand Down

0 comments on commit 018349d

Please sign in to comment.