netdev - RE: [patch net-next v3 01/11] net: devlink: make sure that devlink_try_get() works with valid pointer during xarray iteration

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Message-ID: <SA2PR11MB5100CD9D0CBCDB2D0F76271CD6919@SA2PR11MB5100.namprd11.prod.outlook.com>
Date:   Thu, 21 Jul 2022 18:55:04 +0000
From:   "Keller, Jacob E" <jacob.e.keller@...el.com>
To:     Jiri Pirko <jiri@...nulli.us>
CC:     "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "davem@...emloft.net" <davem@...emloft.net>,
        "kuba@...nel.org" <kuba@...nel.org>,
        "idosch@...dia.com" <idosch@...dia.com>,
        "petrm@...dia.com" <petrm@...dia.com>,
        "pabeni@...hat.com" <pabeni@...hat.com>,
        "edumazet@...gle.com" <edumazet@...gle.com>,
        "mlxsw@...dia.com" <mlxsw@...dia.com>,
        "saeedm@...dia.com" <saeedm@...dia.com>,
        "snelson@...sando.io" <snelson@...sando.io>
Subject: RE: [patch net-next v3 01/11] net: devlink: make sure that
 devlink_try_get() works with valid pointer during xarray iteration



> -----Original Message-----
> From: Jiri Pirko <jiri@...nulli.us>
> Sent: Wednesday, July 20, 2022 10:45 PM
> To: Keller, Jacob E <jacob.e.keller@...el.com>
> Cc: netdev@...r.kernel.org; davem@...emloft.net; kuba@...nel.org;
> idosch@...dia.com; petrm@...dia.com; pabeni@...hat.com;
> edumazet@...gle.com; mlxsw@...dia.com; saeedm@...dia.com;
> snelson@...sando.io
> Subject: Re: [patch net-next v3 01/11] net: devlink: make sure that
> devlink_try_get() works with valid pointer during xarray iteration
> 
> >Is it safe to rcu_read_unlock here while we're still in the middle of the array
> processing? What happens if something else updates the xarray? is the
> for_each_marked safe?
> 
> Sure, you don't need to hold rcu_read_lock during call to xa_for_each_marked.
> The consistency of xarray is itself guaranteed. The only reason to take
> rcu_read_lock outside is that the devlink pointer which is
> rcu_dereference_check()'ed inside xa_for_each_marked() is still valid
> once we devlink_try_get() it.
> 

Excellent, ok. Basically we need the RCU for protecting just the pointer until we get a reference to it separately.

Thanks!

In that case:

Reviewed-by: Jacob Keller <jacob.e.keller@...el.com>