linux-kernel - Re: [PATCH v2] hvc/xen: lock console list traversal

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Message-ID: <76596dba-efb7-eab1-bca9-60ab67823ade@suse.com>
Date:   Tue, 10 Jan 2023 09:06:58 +0100
From:   Juergen Gross <jgross@...e.com>
To:     Roger Pau Monne <roger.pau@...rix.com>,
        linux-kernel@...r.kernel.org
Cc:     xen-devel@...ts.xenproject.org,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Jiri Slaby <jirislaby@...nel.org>,
        Boris Ostrovsky <boris.ostrovsky@...cle.com>,
        Jan Beulich <jbeulich@...e.com>,
        Stefano Stabellini <sstabellini@...nel.org>,
        Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
        linuxppc-dev@...ts.ozlabs.org
Subject: Re: [PATCH v2] hvc/xen: lock console list traversal

On 30.11.22 17:36, Roger Pau Monne wrote:
> The currently lockless access to the xen console list in
> vtermno_to_xencons() is incorrect, as additions and removals from the
> list can happen anytime, and as such the traversal of the list to get
> the private console data for a given termno needs to happen with the
> lock held.  Note users that modify the list already do so with the
> lock taken.
> 
> Adjust current lock takers to use the _irq{save,restore} helpers,
> since the context in which vtermno_to_xencons() is called can have
> interrupts disabled.  Use the _irq{save,restore} set of helpers to
> switch the current callers to disable interrupts in the locked region.
> I haven't checked if existing users could instead use the _irq
> variant, as I think it's safer to use _irq{save,restore} upfront.
> 
> While there switch from using list_for_each_entry_safe to
> list_for_each_entry: the current entry cursor won't be removed as
> part of the code in the loop body, so using the _safe variant is
> pointless.
> 
> Fixes: 02e19f9c7cac ('hvc_xen: implement multiconsole support')
> Signed-off-by: Roger Pau Monné <roger.pau@...rix.com>

Pushed to xen/tip.git for-linus-6.2


Juergen


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