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Date: Mon, 6 Oct 2025 10:26:59 -0700
From: Jakub Kicinski <kuba@kernel.org>
To: "Tantilov, Emil S" <emil.s.tantilov@intel.com>
Cc: Jacob Keller <jacob.e.keller@intel.com>, Przemek Kitszel
 <przemyslaw.kitszel@intel.com>, Andrew Lunn <andrew+netdev@lunn.ch>, "David
 S. Miller" <davem@davemloft.net>, "Eric Dumazet" <edumazet@google.com>,
 Paolo Abeni <pabeni@redhat.com>, "Pavan Kumar Linga"
 <pavan.kumar.linga@intel.com>, Alexander Lobakin
 <aleksander.lobakin@intel.com>, Willem de Bruijn <willemb@google.com>,
 Sridhar Samudrala <sridhar.samudrala@intel.com>, Phani Burra
 <phani.r.burra@intel.com>, Piotr Kwapulinski <piotr.kwapulinski@intel.com>,
 Simon Horman <horms@kernel.org>, Radoslaw Tyl <radoslawx.tyl@intel.com>,
 Jedrzej Jagielski <jedrzej.jagielski@intel.com>, Mateusz Polchlopek
 <mateusz.polchlopek@intel.com>, Anton Nadezhdin
 <anton.nadezhdin@intel.com>, Konstantin Ilichev
 <konstantin.ilichev@intel.com>, Milena Olech <milena.olech@intel.com>,
 <netdev@vger.kernel.org>, <linux-kernel@vger.kernel.org>, Joshua Hay
 <joshua.a.hay@intel.com>, Aleksandr Loktionov
 <aleksandr.loktionov@intel.com>, Chittim Madhu <madhu.chittim@intel.com>,
 Samuel Salin <Samuel.salin@intel.com>
Subject: Re: [PATCH net 3/8] idpf: fix possible race in idpf_vport_stop()
Message-ID: <20251006102659.595825fe@kernel.org>
In-Reply-To: <4a128348-48f9-40d7-b5bf-c3f1af27679c@intel.com>
References: <20251001-jk-iwl-net-2025-10-01-v1-0-49fa99e86600@intel.com>
	<20251001-jk-iwl-net-2025-10-01-v1-3-49fa99e86600@intel.com>
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On Mon, 6 Oct 2025 07:49:32 -0700 Tantilov, Emil S wrote:
> > Argh, please stop using the flag based state machines. They CANNOT
> > replace locking. If there was proper locking in place it wouldn't
> > have mattered when we clear the flag.  
> 
> This patch is resolving a bug in the current logic of how the flag is 
> used (not being atomic and not being cleared properly). I don't think
> there is an existing lock in place to address this issue, though we are
> looking to refactor the code over time to remove and/or limit how these
> flags are used.

Can you share more details about the race? If there is no lock in place
there's always the risk that:

  CPU 0                         CPU 1
 idpf_vport_stop()             whatever()
                                 if (test_bit(UP))
                                  # sees true
                                # !< long IRQ arrives
 test_and_clear(UP)
   ...
   all the rest
   ...
                                # > long IRQ ends
                                proceed but UP isn't really set any more