* [PATCH] KVM: x86: Reacquire kvm->srcu in vcpu_run() if exiting on pending signal
@ 2022-02-24 19:06 Sean Christopherson
2022-02-24 20:49 ` Sean Christopherson
0 siblings, 1 reply; 3+ messages in thread
From: Sean Christopherson @ 2022-02-24 19:06 UTC (permalink / raw)
To: Paolo Bonzini
Cc: Sean Christopherson, Vitaly Kuznetsov, Wanpeng Li, Jim Mattson,
Joerg Roedel, kvm, linux-kernel, Like Xu
Reacquire kvm->srcu in vcpu_run() before returning to the caller if srcu
was dropped to handle pending work. If the task receives a signal, KVM
will exit without reacquiring kvm->srcu, resulting in an unbalanced
unlock kvm_arch_vcpu_ioctl_run(), and eventually hung tasks.
=====================================
WARNING: bad unlock balance detected!
5.17.0-rc3+ #749 Not tainted
-------------------------------------
CPU 0/KVM/1803 is trying to release lock (&kvm->srcu) at:
[<ffffffff81042a19>] kvm_arch_vcpu_ioctl_run+0x669/0x1f60
but there are no more locks to release!
other info that might help us debug this:
1 lock held by CPU 0/KVM/1803:
#0: ffff88810489c0b0 (&vcpu->mutex){....}-{3:3}, at: kvm_vcpu_ioctl+0x77/0x690
stack backtrace:
CPU: 7 PID: 1803 Comm: CPU 0/KVM Not tainted 5.17.0-rc3+ #749
Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 0.0.0 02/06/2015
Call Trace:
<TASK>
dump_stack_lvl+0x34/0x44
lock_release+0x1b4/0x240
kvm_arch_vcpu_ioctl_run+0x680/0x1f60
kvm_vcpu_ioctl+0x279/0x690
__x64_sys_ioctl+0x83/0xb0
do_syscall_64+0x3b/0xc0
entry_SYSCALL_64_after_hwframe+0x44/0xae
</TASK>
INFO: task stable:2347 blocked for more than 120 seconds.
Not tainted 5.17.0-rc3+ #749
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
task:stable state:D stack: 0 pid: 2347 ppid: 2340 flags:0x00000000
Call Trace:
<TASK>
__schedule+0x328/0xa00
schedule+0x44/0xb0
schedule_timeout+0x26f/0x300
wait_for_completion+0x84/0xe0
__synchronize_srcu.part.0+0x7a/0xa0
kvm_swap_active_memslots+0x141/0x180
kvm_set_memslot+0x2f9/0x470
kvm_set_memory_region+0x29/0x40
kvm_vm_ioctl+0x2c3/0xd70
__x64_sys_ioctl+0x83/0xb0
do_syscall_64+0x3b/0xc0
entry_SYSCALL_64_after_hwframe+0x44/0xae
</TASK>
INFO: lockdep is turned off.
Fixes: 5d8d2bfc5e65 ("KVM: x86: pull kvm->srcu read-side to kvm_arch_vcpu_ioctl_run")
Cc: Like Xu <like.xu.linux@gmail.com>
Signed-off-by: Sean Christopherson <seanjc@google.com>
---
arch/x86/kvm/x86.c | 3 ++-
1 file changed, 2 insertions(+), 1 deletion(-)
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index e55de9b48d1a..6de4d810f5b2 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -10281,9 +10281,10 @@ static int vcpu_run(struct kvm_vcpu *vcpu)
if (__xfer_to_guest_mode_work_pending()) {
srcu_read_unlock(&kvm->srcu, vcpu->srcu_idx);
r = xfer_to_guest_mode_handle_work(vcpu);
+ vcpu->srcu_idx = srcu_read_lock(&kvm->srcu);
+
if (r)
return r;
- vcpu->srcu_idx = srcu_read_lock(&kvm->srcu);
}
}
base-commit: 991f988b43c5ee82ef681907bfe979bee93a55c2
--
2.35.1.574.g5d30c73bfb-goog
^ permalink raw reply related [flat|nested] 3+ messages in thread
* Re: [PATCH] KVM: x86: Reacquire kvm->srcu in vcpu_run() if exiting on pending signal
2022-02-24 19:06 [PATCH] KVM: x86: Reacquire kvm->srcu in vcpu_run() if exiting on pending signal Sean Christopherson
@ 2022-02-24 20:49 ` Sean Christopherson
0 siblings, 0 replies; 3+ messages in thread
From: Sean Christopherson @ 2022-02-24 20:49 UTC (permalink / raw)
To: Paolo Bonzini, Vitaly Kuznetsov, Wanpeng Li, Jim Mattson,
Joerg Roedel, kvm, linux-kernel, Like Xu
On Thu, Feb 24, 2022, Sean Christopherson wrote:
> Reacquire kvm->srcu in vcpu_run() before returning to the caller if srcu
> was dropped to handle pending work. If the task receives a signal, KVM
> will exit without reacquiring kvm->srcu, resulting in an unbalanced
> unlock kvm_arch_vcpu_ioctl_run(), and eventually hung tasks.
>
> =====================================
> WARNING: bad unlock balance detected!
> 5.17.0-rc3+ #749 Not tainted
> -------------------------------------
> CPU 0/KVM/1803 is trying to release lock (&kvm->srcu) at:
> [<ffffffff81042a19>] kvm_arch_vcpu_ioctl_run+0x669/0x1f60
> but there are no more locks to release!
>
> other info that might help us debug this:
> 1 lock held by CPU 0/KVM/1803:
> #0: ffff88810489c0b0 (&vcpu->mutex){....}-{3:3}, at: kvm_vcpu_ioctl+0x77/0x690
>
> stack backtrace:
> CPU: 7 PID: 1803 Comm: CPU 0/KVM Not tainted 5.17.0-rc3+ #749
> Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 0.0.0 02/06/2015
> Call Trace:
> <TASK>
> dump_stack_lvl+0x34/0x44
> lock_release+0x1b4/0x240
> kvm_arch_vcpu_ioctl_run+0x680/0x1f60
> kvm_vcpu_ioctl+0x279/0x690
> __x64_sys_ioctl+0x83/0xb0
> do_syscall_64+0x3b/0xc0
> entry_SYSCALL_64_after_hwframe+0x44/0xae
> </TASK>
> INFO: task stable:2347 blocked for more than 120 seconds.
> Not tainted 5.17.0-rc3+ #749
> "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
> task:stable state:D stack: 0 pid: 2347 ppid: 2340 flags:0x00000000
> Call Trace:
> <TASK>
> __schedule+0x328/0xa00
> schedule+0x44/0xb0
> schedule_timeout+0x26f/0x300
> wait_for_completion+0x84/0xe0
> __synchronize_srcu.part.0+0x7a/0xa0
> kvm_swap_active_memslots+0x141/0x180
> kvm_set_memslot+0x2f9/0x470
> kvm_set_memory_region+0x29/0x40
> kvm_vm_ioctl+0x2c3/0xd70
> __x64_sys_ioctl+0x83/0xb0
> do_syscall_64+0x3b/0xc0
> entry_SYSCALL_64_after_hwframe+0x44/0xae
> </TASK>
> INFO: lockdep is turned off.
Ugh, the task hung is actually a different mess introduced by the same patch.
I suspect I'm hitting the one Like reported.
I'll get a fix posted shortly...
^ permalink raw reply [flat|nested] 3+ messages in thread
* Re: [PATCH] KVM: x86: Reacquire kvm->srcu in vcpu_run() if exiting on pending signal
@ 2022-02-25 9:59 Paolo Bonzini
0 siblings, 0 replies; 3+ messages in thread
From: Paolo Bonzini @ 2022-02-25 9:59 UTC (permalink / raw)
To: Sean Christopherson
Cc: linux-kernel, kvm, Vitaly Kuznetsov, Wanpeng Li, Jim Mattson,
Joerg Roedel, Like Xu
Queued, thanks.
Paolo
^ permalink raw reply [flat|nested] 3+ messages in thread
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