[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] Re: xen/evtchn: Interrupt for port 34, but apparently not enabled; per-user 00000000a86a4c1b on 5.10
Hi Juergen, On 15/12/2020 10:20, Jürgen Groß wrote: On 15.12.20 08:27, Jürgen Groß wrote:On 14.12.20 22:25, Julien Grall wrote:Hi Juergen,When testing Linux 5.10 dom0, I could reliably hit the following warning with using event 2L ABI:[ 589.591737] Interrupt for port 34, but apparently not enabled; per-user 00000000a86a4c1b [ 589.593259] WARNING: CPU: 0 PID: 1111 at /home/ANT.AMAZON.COM/jgrall/works/oss/linux/drivers/xen/evtchn.c:170 evtchn_interrupt+0xeb/0x100[ 589.595514] Modules linked in:[ 589.596145] CPU: 0 PID: 1111 Comm: qemu-system-i38 Tainted: G W 5.10.0+ #180 [ 589.597708] Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS rel-1.12.0-59-gc9ba5276e321-prebuilt.qemu.org 04/01/2014[ 589.599782] RIP: e030:evtchn_interrupt+0xeb/0x100[ 589.600698] Code: 48 8d bb d8 01 00 00 ba 01 00 00 00 be 1d 00 00 00 e8 d9 10 ca ff eb b2 8b 75 20 48 89 da 48 c7 c7 a8 31 3d 82 e8 65 29 a0 ff <0f> 0b e9 42 ff ff ff 0f 1f 40 00 66 2e 0f 1f 84 00 00 00 00 00 0f[ 589.604087] RSP: e02b:ffffc90040003e70 EFLAGS: 00010086[ 589.605102] RAX: 0000000000000000 RBX: ffff888102091800 RCX: 0000000000000027 [ 589.606445] RDX: 0000000000000000 RSI: ffff88817fe19150 RDI: ffff88817fe19158 [ 589.607790] RBP: ffff88810f5ab980 R08: 0000000000000001 R09: 0000000000328980 [ 589.609134] R10: 0000000000000000 R11: ffffc90040003c70 R12: ffff888107fd3c00 [ 589.610484] R13: ffffc90040003ed4 R14: 0000000000000000 R15: ffff88810f5ffd80 [ 589.611828] FS: 00007f960c4b8ac0(0000) GS:ffff88817fe00000(0000) knlGS:0000000000000000[ 589.613348] CS: 10000e030 DS: 0000 ES: 0000 CR0: 0000000080050033[ 589.614525] CR2: 00007f17ee72e000 CR3: 000000010f5b6000 CR4: 0000000000050660[ 589.615874] Call Trace: [ 589.616402] <IRQ> [ 589.616855] __handle_irq_event_percpu+0x4e/0x2c0 [ 589.617784] handle_irq_event_percpu+0x30/0x80 [ 589.618660] handle_irq_event+0x3a/0x60 [ 589.619428] handle_edge_irq+0x9b/0x1f0 [ 589.620209] generic_handle_irq+0x4f/0x60 [ 589.621008] evtchn_2l_handle_events+0x160/0x280 [ 589.621913] __xen_evtchn_do_upcall+0x66/0xb0 [ 589.622767] __xen_pv_evtchn_do_upcall+0x11/0x20 [ 589.623665] asm_call_irq_on_stack+0x12/0x20 [ 589.624511] </IRQ> [ 589.624978] xen_pv_evtchn_do_upcall+0x77/0xf0 [ 589.625848] exc_xen_hypervisor_callback+0x8/0x10This can be reproduced when creating/destroying guest in a loop. Although, I have struggled to reproduce it on a vanilla Xen.After several hours of debugging, I think I have found the root cause.While we only expect the unmask to happen when the event channel is EOIed, there is an unmask happening as part of handle_edge_irq() because the interrupt was seen as pending by another vCPU (IRQS_PENDING is set).It turns out that the event channel is set for multiple vCPU is in cpu_evtchn_mask. This is happening because the affinity is not cleared when freeing an event channel.The implementation of evtchn_2l_handle_events() will look for all the active interrupts for the current vCPU and later on clear the pending bit (via the ack() callback). IOW, I believe, this is not an atomic operation.Even if Xen will notify the event to a single vCPU, evtchn_pending_sel may still be set on the other vCPU (thanks to a different event channel). Therefore, there is a chance that two vCPUs will try to handle the same interrupt.The IRQ handler handle_edge_irq() is able to deal with that and will mask/unmask the interrupt. This will mess us with the lateeoi logic (although, I managed to reproduce it once without XSA-332).Thanks for the analysis!My initial idea to fix the problem was to switch the affinity from CPU X to CPU0 when the event channel is freed.However, I am not sure this is enough because I haven't found anything yet preventing a race between evtchn_2l_handle_events9) and evtchn_2l_bind_vcpu().So maybe we want to introduce a refcounting (if there is nothing provided by the IRQ framework) and only unmask when the counter drop to 0.Any opinions?I think we don't need a refcount, but just the internal states "masked" and "eoi_pending" and unmask only if both are false. "masked" will be set when the event is being masked. When delivering a lateeoi irq "eoi_pending" will be set and "masked "reset. "masked" will be reset when a normal unmask is happening. And "eoi_pending" will be reset when a lateeoi is signaled. Any reset of "masked" and "eoi_pending" will check the other flag and do an unmask if both are false. I'll write a patch.Julien, could you please test the attached (only build tested) patch? Thank you writing the patches. I will aim to give a spin next week. Cheers, -- Julien Grall
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