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Message-ID: <47686a61dfc06aa5afb05a893b9a56e6eb46763d.camel@infradead.org>
Subject: Re: [PATCH 2/2] xen: make xen_qlock_wait() nestable
From:   David Woodhouse <dwmw2@infradead.org>
To:     Juergen Gross <jgross@suse.com>, linux-kernel@vger.kernel.org,
        xen-devel@lists.xenproject.org, x86@kernel.org
Cc:     boris.ostrovsky@oracle.com, hpa@zytor.com, tglx@linutronix.de,
        mingo@redhat.com, bp@alien8.de, stable@vger.kernel.org,
        Waiman.Long@hp.com, peterz@infradead.org
Date:   Wed, 10 Oct 2018 12:53:38 +0100
In-Reply-To: <20181001071641.19282-3-jgross@suse.com>
References: <20181001071641.19282-1-jgross@suse.com>
         <20181001071641.19282-3-jgross@suse.com>
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On Mon, 2018-10-01 at 09:16 +0200, Juergen Gross wrote:
> -       /* If irq pending already clear it and return. */
> +       /* Guard against reentry. */
> +       local_irq_save(flags);
> +
> +       /* If irq pending already clear it. */
>         if (xen_test_irq_pending(irq)) {
>                 xen_clear_irq_pending(irq);
> -               return;
> +       } else if (READ_ONCE(*byte) =3D=3D val) {
> +               /* Block until irq becomes pending (or a spurious wakeup)=
 */
> +               xen_poll_irq(irq);
>         }


Does this still allow other IRQs to wake it from xen_poll_irq()?

In the case where process-context code is spinning for a lock without
disabling interrupts, we *should* allow interrupts to occur still...
does this?

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