On Thu, May 30, 2024 at 5:17 PM Michael S. Tsirkin <mst@xxxxxxxxxx> wrote: > > On Tue, May 28, 2024 at 09:41:16PM +0800, Heng Qi wrote: > > 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: 4d4ac2ececd3 ("virtio_net: Add a lock for per queue RX coalesce") > > Signed-off-by: Heng Qi <hengqi@xxxxxxxxxxxxxxxxx> > > > Acked-by: Michael S. Tsirkin <mst@xxxxxxxxxx> > Acked-by: Jason Wang <jasowang@xxxxxxxxxx> Btw, adding notation seems to be another way. Thanks