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Date:   Mon, 30 Oct 2023 17:19:36 -0700 (PDT)
From:   Stefano Stabellini <sstabellini@kernel.org>
To:     Juergen Gross <jgross@suse.com>
cc:     linux-kernel@vger.kernel.org,
        Stefano Stabellini <sstabellini@kernel.org>,
        Oleksandr Tyshchenko <oleksandr_tyshchenko@epam.com>,
        xen-devel@lists.xenproject.org, David Woodhouse <dwmw@amazon.co.uk>
Subject: Re: [PATCH] xen/events: avoid using info_for_irq() in
 xen_send_IPI_one()
In-Reply-To: <20231030142732.1702-1-jgross@suse.com>
Message-ID: <alpine.DEB.2.22.394.2310301719300.1625118@ubuntu-linux-20-04-desktop>
References: <20231030142732.1702-1-jgross@suse.com>
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On Mon, 30 Oct 2023, Juergen Gross wrote:
> xen_send_IPI_one() is being used by cpuhp_report_idle_dead() after
> it calls rcu_report_dead(), meaning that any RCU usage by
> xen_send_IPI_one() is a bad idea.
> 
> Unfortunately xen_send_IPI_one() is using notify_remote_via_irq()
> today, which is using irq_get_chip_data() via info_for_irq(). And
> irq_get_chip_data() in turn is using a maple-tree lookup requiring
> RCU.
> 
> Avoid this problem by caching the ipi event channels in another
> percpu variable, allowing the use notify_remote_via_evtchn() in
> xen_send_IPI_one().
> 
> Fixes: 721255b9826b ("genirq: Use a maple tree for interrupt descriptor management")
> Reported-by: David Woodhouse <dwmw@amazon.co.uk>
> Signed-off-by: Juergen Gross <jgross@suse.com>
> Tested-by: David Woodhouse <dwmw@amazon.co.uk>

Acked-by: Stefano Stabellini <sstabellini@kernel.org>