Re: [PATCH] net: hinic: avoid kernel hung in hinic_get_stats64()

From: maqiao
Date: Thu Jun 30 2022 - 10:35:08 EST




在 2022/6/30 下午5:56, Paolo Abeni 写道:
On Wed, 2022-06-29 at 15:28 +0800, Qiao Ma wrote:
When using hinic device as a bond slave device, and reading device stats of
master bond device, the kernel may hung.

The kernel panic calltrace as follows:
Kernel panic - not syncing: softlockup: hung tasks
Call trace:
native_queued_spin_lock_slowpath+0x1ec/0x31c
dev_get_stats+0x60/0xcc
dev_seq_printf_stats+0x40/0x120
dev_seq_show+0x1c/0x40
seq_read_iter+0x3c8/0x4dc
seq_read+0xe0/0x130
proc_reg_read+0xa8/0xe0
vfs_read+0xb0/0x1d4
ksys_read+0x70/0xfc
__arm64_sys_read+0x20/0x30
el0_svc_common+0x88/0x234
do_el0_svc+0x2c/0x90
el0_svc+0x1c/0x30
el0_sync_handler+0xa8/0xb0
el0_sync+0x148/0x180

And the calltrace of task that actually caused kernel hungs as follows:
__switch_to+124
__schedule+548
schedule+72
schedule_timeout+348
__down_common+188
__down+24
down+104
hinic_get_stats64+44 [hinic]
dev_get_stats+92
bond_get_stats+172 [bonding]
dev_get_stats+92
dev_seq_printf_stats+60
dev_seq_show+24
seq_read_iter+964
seq_read+220
proc_reg_read+164
vfs_read+172
ksys_read+108
__arm64_sys_read+28
el0_svc_common+132
do_el0_svc+40
el0_svc+24
el0_sync_handler+164
el0_sync+324

When getting device stats from bond, kernel will call bond_get_stats().
It first holds the spinlock bond->stats_lock, and then call
hinic_get_stats64() to collect hinic device's stats.
However, hinic_get_stats64() calls `down(&nic_dev->mgmt_lock)` to
protect its critical section, which may schedule current task out.
And if system is under high pressure, the task cannot be woken up
immediately, which eventually triggers kernel hung panic.

Fixes: edd384f682cc ("net-next/hinic: Add ethtool and stats")
Signed-off-by: Qiao Ma <mqaio@xxxxxxxxxxxxxxxxx>

Side note: it looks like that after this patch every section protected
by the mgmt_lock is already under rtnl lock protection, so you could
probably remove the hinic specific lock (in a separate, net-next,
patch).

Please double check the above as I skimmed upon that quickly.
Thank you, I need to carefully check each section will only be called through netlink dev_get_stats().

And I forgot to add prefix "net-next" in patch's title, forgive me...

Thanks,

Paolo