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SubjectRe: [PATCH 0/3] KVM: Make kvm_lock non-raw
[Re: [PATCH 0/3] KVM: Make kvm_lock non-raw] On 16/09/2013 (Mon 18:12) Paul Gortmaker wrote:

> On 13-09-16 10:06 AM, Paolo Bonzini wrote:
> > Paul Gortmaker reported a BUG on preempt-rt kernels, due to taking the
> > mmu_lock within the raw kvm_lock in mmu_shrink_scan. He provided a
> > patch that shrunk the kvm_lock critical section so that the mmu_lock
> > critical section does not nest with it, but in the end there is no reason
> > for the vm_list to be protected by a raw spinlock. Only manipulations
> > of kvm_usage_count and the consequent hardware_enable/disable operations
> > are not preemptable.
> >
> > This small series thus splits the kvm_lock in the "raw" part and the
> > "non-raw" part.
> >
> > Paul, could you please provide your Tested-by?
>
> Sure, I'll go back and see if I can find what triggered it in the
> original report, and give the patches a spin on 3.4.x-rt (and probably
> 3.10.x-rt, since that is where rt-current is presently).

Seems fine on 3.4-rt. On 3.10.10-rt7 it looks like there are other
issues, probably not explicitly related to this patchset (see below).

Paul.
--

e1000e 0000:00:19.0 eth1: removed PHC
assign device 0:0:19.0
pci 0000:00:19.0: irq 43 for MSI/MSI-X
pci 0000:00:19.0: irq 43 for MSI/MSI-X
pci 0000:00:19.0: irq 43 for MSI/MSI-X
pci 0000:00:19.0: irq 43 for MSI/MSI-X
BUG: sleeping function called from invalid context at /home/paul/git/linux-rt/kernel/rtmutex.c:659
in_atomic(): 1, irqs_disabled(): 1, pid: 0, name: swapper/0
2 locks held by swapper/0/0:
#0: (rcu_read_lock){.+.+.+}, at: [<ffffffff8100998a>] kvm_set_irq_inatomic+0x2a/0x4a0
#1: (rcu_read_lock){.+.+.+}, at: [<ffffffff81038800>] kvm_irq_delivery_to_apic_fast+0x60/0x3d0
irq event stamp: 6121390
hardirqs last enabled at (6121389): [<ffffffff819f9ae0>] restore_args+0x0/0x30
hardirqs last disabled at (6121390): [<ffffffff819f9a2a>] common_interrupt+0x6a/0x6f
softirqs last enabled at (0): [< (null)>] (null)
softirqs last disabled at (0): [< (null)>] (null)
Preemption disabled at:[<ffffffff810ebb9a>] cpu_startup_entry+0x1ba/0x430

CPU: 0 PID: 0 Comm: swapper/0 Not tainted 3.10.10-rt7 #2
Hardware name: Dell Inc. OptiPlex 990/0VNP2H, BIOS A17 03/14/2013
ffffffff8201c440 ffff880223603cf0 ffffffff819f177d ffff880223603d18
ffffffff810c90d3 ffff880214a50110 0000000000000001 0000000000000001
ffff880223603d38 ffffffff819f89a4 ffff880214a50110 ffff880214a50110
Call Trace:
<IRQ> [<ffffffff819f177d>] dump_stack+0x19/0x1b
[<ffffffff810c90d3>] __might_sleep+0x153/0x250
[<ffffffff819f89a4>] rt_spin_lock+0x24/0x60
[<ffffffff810ccdd6>] __wake_up+0x36/0x70
[<ffffffff81003bbb>] kvm_vcpu_kick+0x3b/0xd0
[<ffffffff810371a2>] __apic_accept_irq+0x2b2/0x3a0
[<ffffffff810385f7>] kvm_apic_set_irq+0x27/0x30
[<ffffffff8103894e>] kvm_irq_delivery_to_apic_fast+0x1ae/0x3d0
[<ffffffff81038800>] ? kvm_irq_delivery_to_apic_fast+0x60/0x3d0
[<ffffffff81009a8b>] kvm_set_irq_inatomic+0x12b/0x4a0
[<ffffffff8100998a>] ? kvm_set_irq_inatomic+0x2a/0x4a0
[<ffffffff8100c5b3>] kvm_assigned_dev_msi+0x23/0x40
[<ffffffff8113cb38>] handle_irq_event_percpu+0x88/0x3d0
[<ffffffff810ebb7c>] ? cpu_startup_entry+0x19c/0x430
[<ffffffff8113cec8>] handle_irq_event+0x48/0x70
[<ffffffff8113f9b7>] handle_edge_irq+0x77/0x120
[<ffffffff8104c6ae>] handle_irq+0x1e/0x30
[<ffffffff81a035ca>] do_IRQ+0x5a/0xd0
[<ffffffff819f9a2f>] common_interrupt+0x6f/0x6f
<EOI> [<ffffffff819f9ae0>] ? retint_restore_args+0xe/0xe
[<ffffffff810ebb7c>] ? cpu_startup_entry+0x19c/0x430
[<ffffffff810ebb38>] ? cpu_startup_entry+0x158/0x430
[<ffffffff819db767>] rest_init+0x137/0x140
[<ffffffff819db635>] ? rest_init+0x5/0x140
[<ffffffff822fde18>] start_kernel+0x3af/0x3bc
[<ffffffff822fd870>] ? repair_env_string+0x5e/0x5e
[<ffffffff822fd5a5>] x86_64_start_reservations+0x2a/0x2c
[<ffffffff822fd673>] x86_64_start_kernel+0xcc/0xcf

=================================
[ INFO: inconsistent lock state ]
3.10.10-rt7 #2 Not tainted
---------------------------------
inconsistent {HARDIRQ-ON-W} -> {IN-HARDIRQ-W} usage.
swapper/0/0 [HC1[1]:SC0[0]:HE0:SE1] takes:
(&(&(&q->lock)->lock)->wait_lock){?.+.-.}, at: [<ffffffff819f7e98>] rt_spin_lock_slowlock+0x48/0x370
{HARDIRQ-ON-W} state was registered at:
[<ffffffff810fc94d>] __lock_acquire+0x69d/0x20e0
[<ffffffff810feaee>] lock_acquire+0x9e/0x1f0
[<ffffffff819f9090>] _raw_spin_lock+0x40/0x80
[<ffffffff819f7e98>] rt_spin_lock_slowlock+0x48/0x370
[<ffffffff819f89ac>] rt_spin_lock+0x2c/0x60
[<ffffffff810ccdd6>] __wake_up+0x36/0x70
[<ffffffff8109c5ce>] run_timer_softirq+0x1be/0x390
[<ffffffff81092a09>] do_current_softirqs+0x239/0x5b0
[<ffffffff81092db8>] run_ksoftirqd+0x38/0x60
[<ffffffff810c5d7c>] smpboot_thread_fn+0x22c/0x340
[<ffffffff810bbf4d>] kthread+0xcd/0xe0
[<ffffffff81a019dc>] ret_from_fork+0x7c/0xb0
irq event stamp: 6121390
hardirqs last enabled at (6121389): [<ffffffff819f9ae0>] restore_args+0x0/0x30
hardirqs last disabled at (6121390): [<ffffffff819f9a2a>] common_interrupt+0x6a/0x6f
softirqs last enabled at (0): [< (null)>] (null)
softirqs last disabled at (0): [< (null)>] (null)

other info that might help us debug this:
Possible unsafe locking scenario:

CPU0
----
lock(&(&(&q->lock)->lock)->wait_lock);
<Interrupt>
lock(&(&(&q->lock)->lock)->wait_lock);

*** DEADLOCK ***

2 locks held by swapper/0/0:
#0: (rcu_read_lock){.+.+.+}, at: [<ffffffff8100998a>] kvm_set_irq_inatomic+0x2a/0x4a0
#1: (rcu_read_lock){.+.+.+}, at: [<ffffffff81038800>] kvm_irq_delivery_to_apic_fast+0x60/0x3d0

stack backtrace:
CPU: 0 PID: 0 Comm: swapper/0 Not tainted 3.10.10-rt7 #2
Hardware name: Dell Inc. OptiPlex 990/0VNP2H, BIOS A17 03/14/2013
ffffffff8262b550 ffff880223603a40 ffffffff819f177d ffff880223603a90
ffffffff819ec532 0000000000000000 ffffffff00000000 ffff880200000001
0000000000000002 ffffffff8201ccc0 ffffffff810f9040 0000000000000000
Call Trace:
<IRQ> [<ffffffff819f177d>] dump_stack+0x19/0x1b
[<ffffffff819ec532>] print_usage_bug.part.36+0x28b/0x29a
[<ffffffff810f9040>] ? check_usage_backwards+0x150/0x150
[<ffffffff810f9dab>] mark_lock+0x28b/0x6a0
[<ffffffff810fcbf9>] __lock_acquire+0x949/0x20e0
[<ffffffff811091f2>] ? __module_text_address+0x12/0x60
[<ffffffff8110ea8f>] ? is_module_text_address+0x2f/0x60
[<ffffffff810b8408>] ? __kernel_text_address+0x58/0x80
[<ffffffff8104dbb2>] ? print_context_stack+0x62/0xf0
[<ffffffff810feaee>] lock_acquire+0x9e/0x1f0
[<ffffffff819f7e98>] ? rt_spin_lock_slowlock+0x48/0x370
[<ffffffff819f9090>] _raw_spin_lock+0x40/0x80
[<ffffffff819f7e98>] ? rt_spin_lock_slowlock+0x48/0x370
[<ffffffff819f7e98>] rt_spin_lock_slowlock+0x48/0x370
[<ffffffff819f89ac>] rt_spin_lock+0x2c/0x60
[<ffffffff810ccdd6>] __wake_up+0x36/0x70
[<ffffffff81003bbb>] kvm_vcpu_kick+0x3b/0xd0
[<ffffffff810371a2>] __apic_accept_irq+0x2b2/0x3a0
[<ffffffff810385f7>] kvm_apic_set_irq+0x27/0x30
[<ffffffff8103894e>] kvm_irq_delivery_to_apic_fast+0x1ae/0x3d0
[<ffffffff81038800>] ? kvm_irq_delivery_to_apic_fast+0x60/0x3d0
[<ffffffff81009a8b>] kvm_set_irq_inatomic+0x12b/0x4a0
[<ffffffff8100998a>] ? kvm_set_irq_inatomic+0x2a/0x4a0
[<ffffffff8100c5b3>] kvm_assigned_dev_msi+0x23/0x40
[<ffffffff8113cb38>] handle_irq_event_percpu+0x88/0x3d0
[<ffffffff810ebb7c>] ? cpu_startup_entry+0x19c/0x430
[<ffffffff8113cec8>] handle_irq_event+0x48/0x70
[<ffffffff8113f9b7>] handle_edge_irq+0x77/0x120
[<ffffffff8104c6ae>] handle_irq+0x1e/0x30
[<ffffffff81a035ca>] do_IRQ+0x5a/0xd0
[<ffffffff819f9a2f>] common_interrupt+0x6f/0x6f
<EOI> [<ffffffff819f9ae0>] ? retint_restore_args+0xe/0xe
[<ffffffff810ebb7c>] ? cpu_startup_entry+0x19c/0x430
[<ffffffff810ebb38>] ? cpu_startup_entry+0x158/0x430
[<ffffffff819db767>] rest_init+0x137/0x140
[<ffffffff819db635>] ? rest_init+0x5/0x140
[<ffffffff822fde18>] start_kernel+0x3af/0x3bc
[<ffffffff822fd870>] ? repair_env_string+0x5e/0x5e
[<ffffffff822fd5a5>] x86_64_start_reservations+0x2a/0x2c
[<ffffffff822fd673>] x86_64_start_kernel+0xcc/0xcf

>
> Paul.
> --
>
> >
> > Thanks,
> >
> > Paolo
> >
> > Paolo Bonzini (3):
> > KVM: cleanup (physical) CPU hotplug
> > KVM: protect kvm_usage_count with its own spinlock
> > KVM: Convert kvm_lock back to non-raw spinlock
> >
> > Documentation/virtual/kvm/locking.txt | 8 ++++--
> > arch/x86/kvm/mmu.c | 4 +--
> > arch/x86/kvm/x86.c | 8 +++---
> > include/linux/kvm_host.h | 2 +-
> > virt/kvm/kvm_main.c | 51 ++++++++++++++++++-----------------
> > 5 files changed, 40 insertions(+), 33 deletions(-)
> >


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