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Date: Wed, 18 Oct 2023 18:34:26 +0200 From: Antoine Tenart <atenart@...nel.org> To: Stephen Hemminger <stephen@...workplumber.org> Cc: davem@...emloft.net, kuba@...nel.org, pabeni@...hat.com, edumazet@...gle.com, netdev@...r.kernel.org, gregkh@...uxfoundation.org, mhocko@...e.com Subject: Re: [RFC PATCH net-next 0/4] net-sysfs: remove rtnl_trylock/restart_syscall use Quoting Stephen Hemminger (2023-10-18 17:57:17) > The trylock was introduced to deal with lock inversion. > It is not clear how this more complex solution prevents that. Anything specifically in the patch 1 comments is not clear that I can improve? The dead lock happens between rtnl_lock and the refcounting on the attribute kn->active, specifically when unregistering net devices because device_del kernfs_drain will wait for the kn->active refcount to reach KN_DEACTIVATED_BIAS, under an rtnl section. The current solution was making one path to bail out (trylock/restart syscall). The idea here is we can actually bail out of the attribute kn protection (kn->active), while still letting unregistering net devices to wait for the current sysfs operations to complete, by using the net device refcount instead. To simplify, instead of waiting on kn->active in the net device unregistration step, this waits on the net device refcount (netdev_wait_allrefs_any), which is done outside an rtnl section. This way kernfs_drain can complete under its rtnl section even if a call to rtnl_lock is waiting in a sysfs operation. Antoine
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