[Xen-devel] [PATCH] Revert xen: dont fiddle with event channel masking in suspend/resume

[Anchal Agarwal <anchalag@xxxxxxxxxx>]

Hello,

This patch reverts commit e91b2b1194335ca83d8a40fa4e0efd480bf2babe.
evtchn are supposed to be masked during resume by irq subsytem 
however, they are not. This causes special interrupts like PV 
spinlock to cause kernel BUG() as it expects the IRQ to be 
masked. This causes instances that are live migrated successfully 
to crash after few minutes.

Live Migration uses suspend resume and when xen_irq_resume is invoked, 
I saw event channels are not masked. Hence, I reverted this
commit to make LM work. Feelings? Recommendations? Things I missed?

One such stack:
 ------------[ cut here ]------------
 kernel BUG at arch/x86/xen/spinlock.c:75!
 CPU: 0 PID: 675 Comm: kauditd Not tainted 4.14.20-48.30.amzn2.x86_64 #1
 Hardware name: Xen HVM domU, BIOS 4.2.amazon 08/24/2006
 task: ffff880205eedac0 task.stack: ffffc90000e4c000
 RIP: 0010:dummy_handler+0x0/0x10
 RSP: 0018:ffff880207203eb8 EFLAGS: 00010046
 RAX: ffffffff81027f10 RBX: ffff880206ce1b00 RCX: 0000000000000035
 RDX: ffffffff81a81560 RSI: 0000000000000000 RDI: 0000000000000035
 RBP: 0000000000000035 R08: ffff880206800248 R09: ffff880206d03600
 R10: 0000000000000000 R11: 0000000000000040 R12: 0000000000000000
 R13: ffff880207203f04 R14: 0000000000000000 R15: 0000000000000000
 FS:  0000000000000000(0000) GS:ffff880207200000(0000) 
 knlGS:0000000000000000
 CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
 CR2: 0000561cc8dbd2d0 CR3: 0000000001e0a001 CR4: 00000000001606f0
 Call Trace:
  <IRQ>
  __handle_irq_event_percpu+0x40/0x190
  handle_irq_event_percpu+0x30/0x70
  handle_percpu_irq+0x37/0x50
  generic_handle_irq+0x24/0x30
  evtchn_2l_handle_events+0x162/0x280
  __xen_evtchn_do_upcall+0x42/0x80
  xen_evtchn_do_upcall+0x27/0x40
  xen_hvm_callback_vector+0x98/0xa0
  </IRQ>
 RIP: 0010:finish_task_switch+0x7b/0x200
 RSP: 0018:ffffc90000e4fe08 EFLAGS: 00000246 ORIG_RAX: ffffffffffffff0c
 RAX: 0000000000000001 RBX: ffff880205eedac0 RCX: 0000000000000000
 RDX: 0000000000000000 RSI: 0000000000000000 RDI: ffff8802072211c0
 RBP: ffffc90000e4fe30 R08: 0000003876060000 R09: 0000000000000000
 R10: 0000000000000000 R11: 0000000000000040 R12: ffff8802072211c0
 R13: ffffffff81e12480 R14: ffff880202e54c00 R15: 0000000000000000
  ? finish_task_switch+0x74/0x200
  __schedule+0x29c/0x8a0
  ? __wake_up_common_lock+0x89/0xc0
  ? kauditd_send_multicast_skb+0x90/0x90
  schedule+0x28/0x80
  kauditd_thread+0x177/0x220
  ? finish_wait+0x80/0x80
  ? auditd_reset+0x90/0x90
  kthread+0x11a/0x130
  ? kthread_create_on_node+0x70/0x70
  ? call_usermodehelper_exec_async+0x12a/0x160
  ret_from_fork+0x35/0x40
  RIP: dummy_handler+0x0/0x10 RSP: ffff880207203eb8

Signed-off-by: Anchal Agarwal <anchalag@xxxxxxxxxx>
Signed-off-by: Eduardo Valentin <eduval@xxxxxxxxxx>
Reviewed-by: Frank van der Linden <fllinden@xxxxxxxxxx>
Reviewed-by: Alakesh Haloi <alakeshh@xxxxxxxxxx>
Reviewed-by: Vallish Vaidyeshwara <vallish@xxxxxxxxxx>

---
 drivers/xen/events/events_base.c | 13 ++++++++++---
 1 file changed, 10 insertions(+), 3 deletions(-)

diff --git a/drivers/xen/events/events_base.c b/drivers/xen/events/events_base.c
index bc03f1a6ad1b..ae71cab207f7 100644
--- a/drivers/xen/events/events_base.c
+++ b/drivers/xen/events/events_base.c
@@ -343,6 +343,14 @@ static void bind_evtchn_to_cpu(unsigned int chn, unsigned 
int cpu)
        info->cpu = cpu;
 }
 
+static void xen_evtchn_mask_all(void)
+{
+       unsigned int evtchn;
+
+       for (evtchn = 0; evtchn < xen_evtchn_nr_channels(); evtchn++)
+               mask_evtchn(evtchn);
+}
+
 /**
  * notify_remote_via_irq - send event to remote end of event channel via irq
  * @irq: irq of event channel to send event to
@@ -1565,6 +1573,7 @@ void xen_irq_resume(void)
        struct irq_info *info;
 
        /* New event-channel space is not 'live' yet. */
+       xen_evtchn_mask_all();
        xen_evtchn_resume();
 
        /* No IRQ <-> event-channel mappings. */
@@ -1682,7 +1691,6 @@ module_param(fifo_events, bool, 0);
 void __init xen_init_IRQ(void)
 {
        int ret = -EINVAL;
-       unsigned int evtchn;
 
        if (fifo_events)
                ret = xen_evtchn_fifo_init();
@@ -1694,8 +1702,7 @@ void __init xen_init_IRQ(void)
        BUG_ON(!evtchn_to_irq);
 
        /* No event channels are 'live' right now. */
-       for (evtchn = 0; evtchn < xen_evtchn_nr_channels(); evtchn++)
-               mask_evtchn(evtchn);
+       xen_evtchn_mask_all();
 
        pirq_needs_eoi = pirq_needs_eoi_flag;
 
-- 
2.14.3


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