When the following snippet is run, lockdep will report a deadlock[1].
/* Acquire all queues dim_locks */
for (i = 0; i < vi->max_queue_pairs; i++)
mutex_lock(&vi->rq[i].dim_lock);
There's no deadlock here because the vq locks are always taken
in the same order, but lockdep can not figure it out. So refactoring
the code to alleviate the problem.
[1]
========================================================
WARNING: possible recursive locking detected
6.9.0-rc7+ #319 Not tainted
--------------------------------------------
ethtool/962 is trying to acquire lock:
but task is already holding lock:
other info that might help us debug this:
Possible unsafe locking scenario:
CPU0
----
lock(&vi->rq[i].dim_lock);
lock(&vi->rq[i].dim_lock);
*** DEADLOCK ***
May be due to missing lock nesting notation
3 locks held by ethtool/962:
#0: ffffffff82dbaab0 (cb_lock){++++}-{3:3}, at: genl_rcv+0x19/0x40
#1: ffffffff82dad0a8 (rtnl_mutex){+.+.}-{3:3}, at:
ethnl_default_set_doit+0xbe/0x1e0
stack backtrace:
CPU: 6 PID: 962 Comm: ethtool Not tainted 6.9.0-rc7+ #319
Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS
rel-1.16.0-0-gd239552ce722-prebuilt.qemu.org 04/01/2014
Call Trace:
<TASK>
dump_stack_lvl+0x79/0xb0
check_deadlock+0x130/0x220
__lock_acquire+0x861/0x990
lock_acquire.part.0+0x72/0x1d0
? lock_acquire+0xf8/0x130
__mutex_lock+0x71/0xd50
virtnet_set_coalesce+0x151/0x190
__ethnl_set_coalesce.isra.0+0x3f8/0x4d0
ethnl_set_coalesce+0x34/0x90
ethnl_default_set_doit+0xdd/0x1e0
genl_family_rcv_msg_doit+0xdc/0x130
genl_family_rcv_msg+0x154/0x230
? __pfx_ethnl_default_set_doit+0x10/0x10
genl_rcv_msg+0x4b/0xa0
? __pfx_genl_rcv_msg+0x10/0x10
netlink_rcv_skb+0x5a/0x110
genl_rcv+0x28/0x40
netlink_unicast+0x1af/0x280
netlink_sendmsg+0x20e/0x460
__sys_sendto+0x1fe/0x210
? find_held_lock+0x2b/0x80
? do_user_addr_fault+0x3a2/0x8a0
? __lock_release+0x5e/0x160
? do_user_addr_fault+0x3a2/0x8a0
? lock_release+0x72/0x140
? do_user_addr_fault+0x3a7/0x8a0
__x64_sys_sendto+0x29/0x30
do_syscall_64+0x78/0x180
entry_SYSCALL_64_after_hwframe+0x76/0x7e
Fixes: 4d4ac2ecec ("virtio_net: Add a lock for per queue RX coalesce")
Signed-off-by: Heng Qi <hengqi@linux.alibaba.com>
Acked-by: Michael S. Tsirkin <mst@redhat.com>
Reviewed-by: Xuan Zhuo <xuanzhuo@linux.alibaba.com>
Acked-by: Jason Wang <jasowang@redhat.com>
Link: https://lore.kernel.org/r/20240528134116.117426-3-hengqi@linux.alibaba.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
d1f0bd01bc