linux-kernel - Re: [PATCH 2/2] xen: make xen_qlock

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Date:   Wed, 10 Oct 2018 12:53:38 +0100
From:   David Woodhouse <dwmw2@...radead.org>
To:     Juergen Gross <jgross@...e.com>, linux-kernel@...r.kernel.org,
        xen-devel@...ts.xenproject.org, x86@...nel.org
Cc:     boris.ostrovsky@...cle.com, hpa@...or.com, tglx@...utronix.de,
        mingo@...hat.com, bp@...en8.de, stable@...r.kernel.org,
        Waiman.Long@...com, peterz@...radead.org
Subject: Re: [PATCH 2/2] xen: make xen_qlock_wait() nestable

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) == 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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