From: "Jürgen Groß" <jgross@suse.com>
To: Julien Grall <julien@xen.org>,
xen-devel@lists.xenproject.org, linux-kernel@vger.kernel.org
Cc: Boris Ostrovsky <boris.ostrovsky@oracle.com>,
Stefano Stabellini <sstabellini@kernel.org>
Subject: Re: [PATCH v2 3/8] xen/events: avoid handling the same event on two cpus at the same time
Date: Mon, 15 Feb 2021 07:55:14 +0100 [thread overview]
Message-ID: <c4d930c1-331f-6a1e-7d26-cf066cecda33@suse.com> (raw)
In-Reply-To: <eed12192-a740-e767-1762-828c75de66ce@xen.org>
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On 14.02.21 22:34, Julien Grall wrote:
> Hi Juergen,
>
> On 11/02/2021 10:16, Juergen Gross wrote:
>> When changing the cpu affinity of an event it can happen today that
>> (with some unlucky timing) the same event will be handled on the old
>> and the new cpu at the same time.
>>
>> Avoid that by adding an "event active" flag to the per-event data and
>> call the handler only if this flag isn't set.
>>
>> Reported-by: Julien Grall <julien@xen.org>
>> Signed-off-by: Juergen Gross <jgross@suse.com>
>> ---
>> V2:
>> - new patch
>> ---
>> drivers/xen/events/events_base.c | 19 +++++++++++++++----
>> 1 file changed, 15 insertions(+), 4 deletions(-)
>>
>> diff --git a/drivers/xen/events/events_base.c
>> b/drivers/xen/events/events_base.c
>> index e157e7506830..f7e22330dcef 100644
>> --- a/drivers/xen/events/events_base.c
>> +++ b/drivers/xen/events/events_base.c
>> @@ -102,6 +102,7 @@ struct irq_info {
>> #define EVT_MASK_REASON_EXPLICIT 0x01
>> #define EVT_MASK_REASON_TEMPORARY 0x02
>> #define EVT_MASK_REASON_EOI_PENDING 0x04
>> + u8 is_active; /* Is event just being handled? */
>> unsigned irq;
>> evtchn_port_t evtchn; /* event channel */
>> unsigned short cpu; /* cpu bound */
>> @@ -622,6 +623,7 @@ static void xen_irq_lateeoi_locked(struct irq_info
>> *info, bool spurious)
>> }
>> info->eoi_time = 0;
>> + smp_store_release(&info->is_active, 0);
>> do_unmask(info, EVT_MASK_REASON_EOI_PENDING);
>> }
>> @@ -809,13 +811,15 @@ static void pirq_query_unmask(int irq)
>> static void eoi_pirq(struct irq_data *data)
>> {
>> - evtchn_port_t evtchn = evtchn_from_irq(data->irq);
>> + struct irq_info *info = info_for_irq(data->irq);
>> + evtchn_port_t evtchn = info ? info->evtchn : 0;
>> struct physdev_eoi eoi = { .irq = pirq_from_irq(data->irq) };
>> int rc = 0;
>> if (!VALID_EVTCHN(evtchn))
>> return;
>> + smp_store_release(&info->is_active, 0);
>
> Would you mind to explain why you are using the release semantics?
It is basically releasing a lock. So release semantics seem to be
appropriate.
> It is also not clear to me if there are any expected ordering between
> clearing is_active and clearing the pending bit.
No, I don't think there is a specific ordering required. is_active is
just guarding against two simultaneous IRQ handler calls for the same
event being active. Clearing the pending bit is not part of the guarded
section.
>
>> clear_evtchn(evtchn);
>
>
> The 2 lines here seems to be a common pattern in this patch. So I would
> suggest to create a new helper.
Okay.
Juergen
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next prev parent reply other threads:[~2021-02-15 6:55 UTC|newest]
Thread overview: 21+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-02-11 10:16 [PATCH v2 0/8] xen/events: bug fixes and some diagnostic aids Juergen Gross
2021-02-11 10:16 ` [PATCH v2 1/8] xen/events: reset affinity of 2-level event when tearing it down Juergen Gross
2021-02-14 21:17 ` Julien Grall
2021-02-11 10:16 ` [PATCH v2 2/8] xen/events: don't unmask an event channel when an eoi is pending Juergen Gross
2021-02-11 10:16 ` [PATCH v2 3/8] xen/events: avoid handling the same event on two cpus at the same time Juergen Gross
2021-02-14 21:34 ` Julien Grall
2021-02-15 6:55 ` Jürgen Groß [this message]
2021-02-15 21:35 ` Boris Ostrovsky
2021-02-18 11:47 ` Jürgen Groß
2021-02-11 10:16 ` [PATCH v2 4/8] xen/netback: fix spurious event detection for common event case Juergen Gross
2021-02-11 10:53 ` Jan Beulich
2021-02-11 14:15 ` Paul Durrant
2021-02-11 15:24 ` Wei Liu
2021-02-11 10:16 ` [PATCH v2 5/8] xen/events: link interdomain events to associated xenbus device Juergen Gross
2021-02-11 14:16 ` Paul Durrant
2021-02-11 10:16 ` [PATCH v2 6/8] xen/events: add per-xenbus device event statistics and settings Juergen Gross
2021-02-15 21:54 ` Boris Ostrovsky
2021-02-11 10:16 ` [PATCH v2 7/8] xen/evtch: use smp barriers for user event ring Juergen Gross
2021-02-11 10:16 ` [PATCH v2 8/8] xen/evtchn: use READ/WRITE_ONCE() for accessing ring indices Juergen Gross
2021-02-17 13:29 ` Ross Lagerwall
2021-02-18 11:46 ` Jürgen Groß
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