Re: [PATCH] net: ethernet: mediatek: fixed deadlock captured by lockdep

[David Miller]

From: 
Date: Tue, 4 Jul 2017 11:17:36 +0800

> From: Sean Wang 
> 
> Lockdep found an inconsistent lock state when mtk_get_stats64 is called
> in user context while NAPI updates MAC statistics in softirq.
> 
> Use spin_trylock_bh/spin_unlock_bh fix following lockdep warning.
 ...
> Signed-off-by: Sean Wang 

Good catch, applied, thanks.

[PATCH] net: ethernet: mediatek: fixed deadlock captured by lockdep

[sean.wang]

From: Sean Wang 

Lockdep found an inconsistent lock state when mtk_get_stats64 is called
in user context while NAPI updates MAC statistics in softirq.

Use spin_trylock_bh/spin_unlock_bh fix following lockdep warning.

[   81.321030] WARNING: inconsistent lock state
[   81.325266] 4.12.0-rc1-00035-gd9dda65 #32 Not tainted
[   81.330273] 
[   81.334505] inconsistent {SOFTIRQ-ON-W} -> {IN-SOFTIRQ-W} usage.
[   81.340464] ksoftirqd/0/7 [HC0[0]:SC1[1]:HE1:SE0] takes:
[   81.345731]  (>seq#2){+.?...}, at: [] 
mtk_handle_status_irq.part.6+0x70/0x84
[   81.354219] {SOFTIRQ-ON-W} state was registered at:
[   81.359062]   lock_acquire+0xfc/0x2b0
[   81.362696]   mtk_stats_update_mac+0x60/0x2c0
[   81.367017]   mtk_get_stats64+0x17c/0x18c
[   81.370995]   dev_get_stats+0x48/0xbc
[   81.374628]   rtnl_fill_stats+0x48/0x128
[   81.378520]   rtnl_fill_ifinfo+0x4ac/0xd1c
[   81.382584]   rtmsg_ifinfo_build_skb+0x7c/0xe0
[   81.386991]   rtmsg_ifinfo.part.5+0x24/0x54
[   81.391139]   rtmsg_ifinfo+0x24/0x28
[   81.394685]   __dev_notify_flags+0xa4/0xac
[   81.398749]   dev_change_flags+0x50/0x58
[   81.402640]   devinet_ioctl+0x768/0x85c
[   81.406444]   inet_ioctl+0x1a4/0x1d0
[   81.409990]   sock_ioctl+0x16c/0x33c
[   81.413538]   do_vfs_ioctl+0xb4/0xa34
[   81.417169]   SyS_ioctl+0x44/0x6c
[   81.420458]   ret_fast_syscall+0x0/0x1c
[   81.424260] irq event stamp: 3354692
[   81.427806] hardirqs last  enabled at (3354692): [] 
net_rx_action+0xc0/0x504
[   81.435660] hardirqs last disabled at (3354691): [] 
net_rx_action+0x8c/0x504
[   81.443515] softirqs last  enabled at (3354106): [] 
__do_softirq+0x4b4/0x614
[   81.451370] softirqs last disabled at (3354109): [] 
run_ksoftirqd+0x44/0x80
[   81.459134]
[   81.459134] other info that might help us debug this:
[   81.465608]  Possible unsafe locking scenario:
[   81.465608]
[   81.471478]CPU0
[   81.473900]
[   81.476321]   lock(>seq#2);
[   81.479701]   
[   81.482294] lock(>seq#2);
[   81.485847]
[   81.485847]  *** DEADLOCK ***
[   81.485847]
[   81.491720] 1 lock held by ksoftirqd/0/7:
[   81.495693]  #0:  (&(>hw_stats->stats_lock)->rlock){+.+...}, at: 
[] mtk_handle_status_irq.part.6+0x48/0x84
[   81.506579]
[   81.506579] stack backtrace:
[   81.510904] CPU: 0 PID: 7 Comm: ksoftirqd/0 Not tainted 
4.12.0-rc1-00035-gd9dda65 #32
[   81.518668] Hardware name: Mediatek Cortex-A7 (Device Tree)
[   81.524208] [] (unwind_backtrace) from [] 
(show_stack+0x20/0x24)
[   81.531899] [] (show_stack) from [] 
(dump_stack+0xb4/0xe0)
[   81.539072] [] (dump_stack) from [] 
(print_usage_bug+0x234/0x2e0)
[   81.546846] [] (print_usage_bug) from [] 
(mark_lock+0x63c/0x7bc)
[   81.554532] [] (mark_lock) from [] 
(__lock_acquire+0x654/0x1bfc)
[   81.562217] [] (__lock_acquire) from [] 
(lock_acquire+0xfc/0x2b0)
[   81.569990] [] (lock_acquire) from [] 
(mtk_stats_update_mac+0x60/0x2c0)
[   81.578283] [] (mtk_stats_update_mac) from [] 
(mtk_handle_status_irq.part.6+0x70/0x84)
[   81.587865] [] (mtk_handle_status_irq.part.6) from [] 
(mtk_napi_tx+0x358/0x37c)
[   81.596845] [] (mtk_napi_tx) from [] 
(net_rx_action+0x244/0x504)
[   81.604533] [] (net_rx_action) from [] 
(__do_softirq+0x134/0x614)
[   81.612306] [] (__do_softirq) from [] 
(run_ksoftirqd+0x44/0x80)
[   81.619907] [] (run_ksoftirqd) from [] 
(smpboot_thread_fn+0x14c/0x25c)
[   81.628110] [] (smpboot_thread_fn) from [] 
(kthread+0x150/0x180)
[   81.635798] [] (kthread) from [] 
(ret_from_fork+0x14/0x24)

Signed-off-by: Sean Wang 
---
 drivers/net/ethernet/mediatek/mtk_eth_soc.c | 8 
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/drivers/net/ethernet/mediatek/mtk_eth_soc.c 
b/drivers/net/ethernet/mediatek/mtk_eth_soc.c
index 16f9755..8a2acb8 100644
--- a/drivers/net/ethernet/mediatek/mtk_eth_soc.c
+++ b/drivers/net/ethernet/mediatek/mtk_eth_soc.c
@@ -470,9 +470,9 @@ static void mtk_get_stats64(struct net_device *dev,
unsigned int start;
 
if (netif_running(dev) && netif_device_present(dev)) {
-   if (spin_trylock(_stats->stats_lock)) {
+   if (spin_trylock_bh(_stats->stats_lock)) {
mtk_stats_update_mac(mac);
-   spin_unlock(_stats->stats_lock);
+   spin_unlock_bh(_stats->stats_lock);
}
}
 
@@ -2156,9 +2156,9 @@ static void mtk_get_ethtool_stats(struct net_device *dev,
return;
 
if (netif_running(dev) && netif_device_present(dev)) {
-   if (spin_trylock(>stats_lock)) {
+   if (spin_trylock_bh(>stats_lock)) {
mtk_stats_update_mac(mac);
-   spin_unlock(>stats_lock);
+   spin_unlock_bh(>stats_lock);
}
}
 
-- 
2.7.4