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[3.8.y.z,extended,stable] Patch "KVM: x86: fix deadlock in clock-in-progress request handling" has been added to staging queue

Message ID 1372445003-23723-1-git-send-email-kamal@canonical.com
State New
Headers show

Commit Message

Kamal Mostafa June 28, 2013, 6:43 p.m. UTC 
This is a note to let you know that I have just added a patch titled

    KVM: x86: fix deadlock in clock-in-progress request handling

to the linux-3.8.y-queue branch of the 3.8.y.z extended stable tree 
which can be found at:

 http://kernel.ubuntu.com/git?p=ubuntu/linux.git;a=shortlog;h=refs/heads/linux-3.8.y-queue

This patch is scheduled to be released in version 3.8.13.4.

If you, or anyone else, feels it should not be added to this tree, please 
reply to this email.

For more information about the 3.8.y.z tree, see
https://wiki.ubuntu.com/Kernel/Dev/ExtendedStable

Thanks.
-Kamal

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From 17ff438a9b1605e84d37d0f7285f71e2c920468d Mon Sep 17 00:00:00 2001
From: Marcelo Tosatti <mtosatti@redhat.com>
Date: Mon, 18 Mar 2013 13:54:32 -0300
Subject: KVM: x86: fix deadlock in clock-in-progress request handling

commit c09664bb44184b3846e8c5254db4eae4b932682a upstream.

There is a deadlock in pvclock handling:

cpu0:                                               cpu1:
kvm_gen_update_masterclock()
                                              kvm_guest_time_update()
 spin_lock(pvclock_gtod_sync_lock)
                                               local_irq_save(flags)

spin_lock(pvclock_gtod_sync_lock)

 kvm_make_mclock_inprogress_request(kvm)
  make_all_cpus_request()
   smp_call_function_many()

Now if smp_call_function_many() called by cpu0 tries to call function on
cpu1 there will be a deadlock.

Fix by moving pvclock_gtod_sync_lock protected section outside irq
disabled section.

Analyzed by Gleb Natapov <gleb@redhat.com>
Acked-by: Gleb Natapov <gleb@redhat.com>
Reported-and-Tested-by: Yongjie Ren <yongjie.ren@intel.com>
Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com>
Signed-off-by: Kamal Mostafa <kamal@canonical.com>
---
 arch/x86/kvm/x86.c | 18 +++++++++---------
 1 file changed, 9 insertions(+), 9 deletions(-)

--
1.8.1.2
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Patch

diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index ff74a2c..6e2af7b 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -1416,15 +1416,6 @@  static int kvm_guest_time_update(struct kvm_vcpu *v)
 	kernel_ns = 0;
 	host_tsc = 0;

-	/* Keep irq disabled to prevent changes to the clock */
-	local_irq_save(flags);
-	this_tsc_khz = __get_cpu_var(cpu_tsc_khz);
-	if (unlikely(this_tsc_khz == 0)) {
-		local_irq_restore(flags);
-		kvm_make_request(KVM_REQ_CLOCK_UPDATE, v);
-		return 1;
-	}
-
 	/*
 	 * If the host uses TSC clock, then passthrough TSC as stable
 	 * to the guest.
@@ -1436,6 +1427,15 @@  static int kvm_guest_time_update(struct kvm_vcpu *v)
 		kernel_ns = ka->master_kernel_ns;
 	}
 	spin_unlock(&ka->pvclock_gtod_sync_lock);
+
+	/* Keep irq disabled to prevent changes to the clock */
+	local_irq_save(flags);
+	this_tsc_khz = __get_cpu_var(cpu_tsc_khz);
+	if (unlikely(this_tsc_khz == 0)) {
+		local_irq_restore(flags);
+		kvm_make_request(KVM_REQ_CLOCK_UPDATE, v);
+		return 1;
+	}
 	if (!use_master_clock) {
 		host_tsc = native_read_tsc();
 		kernel_ns = get_kernel_ns();