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Message-ID: <20231017085146.GL1751252@kernel.org> Date: Tue, 17 Oct 2023 10:51:46 +0200 From: Simon Horman <horms@...nel.org> To: Jiri Pirko <jiri@...nulli.us> Cc: netdev@...r.kernel.org, kuba@...nel.org, pabeni@...hat.com, davem@...emloft.net, edumazet@...gle.com Subject: Re: [patch net-next v3 4/7] devlink: don't take instance lock for nested handle put On Fri, Oct 13, 2023 at 02:10:26PM +0200, Jiri Pirko wrote: > From: Jiri Pirko <jiri@...dia.com> > > Lockdep reports following issue: > > WARNING: possible circular locking dependency detected > ------------------------------------------------------ > devlink/8191 is trying to acquire lock: > ffff88813f32c250 (&devlink->lock_key#14){+.+.}-{3:3}, at: devlink_rel_devlink_handle_put+0x11e/0x2d0 > > but task is already holding lock: > ffffffff8511eca8 (rtnl_mutex){+.+.}-{3:3}, at: unregister_netdev+0xe/0x20 > > which lock already depends on the new lock. > > the existing dependency chain (in reverse order) is: > > -> #3 (rtnl_mutex){+.+.}-{3:3}: ... > Possible unsafe locking scenario: > > CPU0 CPU1 > ---- ---- > lock(rtnl_mutex); > lock(mlx5_intf_mutex); > lock(rtnl_mutex); > lock(&devlink->lock_key#14); > > Problem is taking the devlink instance lock of nested instance when RTNL > is already held. > > To fix this, don't take the devlink instance lock when putting nested > handle. Instead, rely on the preparations done by previous two patches > to be able to access device pointer and obtain netns id without devlink > instance lock held. > > Fixes: c137743bce02 ("devlink: introduce object and nested devlink relationship infra") > Signed-off-by: Jiri Pirko <jiri@...dia.com> Reviewed-by: Simon Horman <horms@...nel.org>
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