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Message-ID: <9a08bbf2-ba6a-6e49-3bcb-bfe2beb32b99@xen.org>
Date: Tue, 22 Jun 2021 14:21:18 +0200
From: Julien Grall <julien@....org>
To: Juergen Gross <jgross@...e.com>
Cc: "xen-devel@...ts.xenproject.org" <xen-devel@...ts.xenproject.org>,
linux-kernel@...r.kernel.org, mheyne@...zon.de
Subject: Re: Interrupt for port 19, but apparently not enabled; per-user
000000004af23acc
Hi Juergen,
On 22/06/2021 13:04, Juergen Gross wrote:
> On 22.06.21 12:24, Julien Grall wrote:
>> Hi Juergen,
>>
>> As discussed on IRC yesterday, we noticed a couple of splat in 5.13-rc6
>
>> (and stable 5.4) in the evtchn driver:
>>
>> [ 7.581000] ------------[ cut here ]------------
>> [ 7.581899] Interrupt for port 19, but apparently not
> enabled;
>> per-user 000000004af23acc
>> [ 7.583401] WARNING: CPU: 0 PID: 467 at
>> /home/ANT.AMAZON.COM/jgrall/works/oss/linux/drivers/xen/evtchn.c:169
>> evtchn_interrupt+0xd5/0x100
>> [ 7.585583] Modules linked in:
>> [ 7.586188] CPU: 0 PID: 467 Comm: xenstore-read Not tainted
>> 5.13.0-rc6 #240
>> [ 7.587462] Hardware name: QEMU Standard PC (Q35 + ICH9, 2009),
>> BIOS rel-1.14.0-0-g155821a1990b-prebuilt.qemu.org 04/01/2014
>> [ 7.589462] RIP: e030:evtchn_interrupt+0xd5/0x100
>> [ 7.590361] Code: 48 8d bb d8 01 00 00 ba 01 00 00 00
> be 1d 00 00 00
>> e8 5f 72 c4 ff eb b2 8b 75 20 48 89 da 48 c7 c7 a8 03 5f 82 e8 6b 2d 96
>
>> ff <0f> 0b e9 4d ff ff ff 41 0f b6 f4 48 c7 c7 80 da a2 82 e8 f0
>> [ 7.593662] RSP: e02b:ffffc90040003e60 EFLAGS: 00010082
>> [ 7.594636] RAX: 0000000000000000 RBX: ffff888102328c00 RCX:
>> 0000000000000027
>> [ 7.595924] RDX: 0000000000000000 RSI: ffff88817fe18ad0 RDI:
>> ffff88817fe18ad8
>> [ 7.597216] RBP: ffff888108ef8140 R08: 0000000000000000 R09:
>> 0000000000000001
>> [ 7.598522] R10: 0000000000000000 R11: 7075727265746e49 R12:
>> 0000000000000000
>> [ 7.599810] R13: ffffc90040003ec4 R14: ffff8881001b8000 R15:
>> ffff888109b36f80
>> [ 7.601113] FS: 0000000000000000(0000) GS:ffff88817fe00000(0000)
>> knlGS:0000000000000000
>> [ 7.602570] CS: 10000e030 DS: 0000 ES: 0000 CR0: 0000000080050033
>> [ 7.603700] CR2: 00007f15b390e368 CR3: 000000010bb04000 CR4:
>> 0000000000050660
>> [ 7.604993] Call Trace:
>> [ 7.605501] <IRQ>
>> [ 7.605929] __handle_irq_event_percpu+0x4c/0x330
>> [ 7.606817] handle_irq_event_percpu+0x32/0xa0
>> [ 7.607670] handle_irq_event+0x3a/0x60
>> [ 7.608416] handle_edge_irq+0x9b/0x1f0
>> [ 7.609154] generic_handle_irq+0x4f/0x60
>> [ 7.609918] __evtchn_fifo_handle_events+0x195/0x3a0
>> [ 7.610864] __xen_evtchn_do_upcall+0x66/0xb0
>> [ 7.611693] __xen_pv_evtchn_do_upcall+0x1d/0x30
>> [ 7.612582] xen_pv_evtchn_do_upcall+0x9d/0xc0
>> [ 7.613439] </IRQ>
>> [ 7.613882] exc_xen_hypervisor_callback+0x8/0x10
>>
>> This is quite similar to the problem I reported a few months ago (see
>> [1]) but this time this is happening with fifo rather than 2L.
>>
>> I haven't been able to reproduced it reliably so far. But looking at
>> the code, I think I have found another potential race after commit
>>
>> commit b6622798bc50b625a1e62f82c7190df40c1f5b21
>> Author: Juergen Gross <jgross@...e.com>
>> Date: Sat Mar 6 17:18:33 2021 +0100
>> xen/events: avoid handling the same event on two cpus at the same
>> time
>> 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.
>> Cc: stable@...r.kernel.org
>> Reported-by: Julien Grall <julien@....org>
>> Signed-off-by: Juergen Gross <jgross@...e.com>
>> Reviewed-by: Julien Grall <jgrall@...zon.com>
>> Link: https://lore.kernel.org/r/20210306161833.4552-4-jgross@suse.com
>> Signed-off-by: Boris Ostrovsky <boris.ostrovsky@...cle.com>
>>
>> The evtchn driver will use the lateeoi handlers. So the code to ack
>> looks like:
>>
>> do_mask(..., EVT_MASK_REASON_EOI_PENDING)
>> smp_store_release(&info->is_active, 0);
>> clear_evtchn(info->evtchn);
>>
>> The code to handle an interrupts look like:
>>
>> clear_link(...)
>> if ( evtchn_fifo_is_pending(port) && !evtchn_fifo_is_mask()) {
>> if (xchg_acquire(&info->is_active, 1)
>> return;
>> generic_handle_irq();
>> }
>>
>> After changing the affinity, an interrupt may be received once on the
>> previous vCPU. So, I think the following can happen:
>>
>> vCPU0 | vCPU1
>> |
>> Receive event |
>> | change affinity to vCPU1
>> clear_link() |
>> |
>> /* The interrupt is re-raised */
>> | receive event
>> |
>> | /* The interrupt is not masked */
>> info->is_active = 1 |
>> do_mask(...) |
>> info->is_active = 0 |
>> | info->is_active = 1
>> clear_evtchn(...) |
>> | do_mask(...)
>> | info->is_active = 0
>> | clear_evtchn(...)
>>
>> Does this look plausible to you?
>
> Yes, it does.
>
> Thanks for the analysis.
>
> So I guess for lateeoi events we need to clear is_active only in
> xen_irq_lateeoi()? At a first glance this should fix the issue.
It should work and would be quite neat. But, I believe clear_evtchn()
would have to stick in the ack helper to avoid losing interrupts.
Cheers,
--
Julien Grall
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