Messages in this thread | | | Date | Mon, 13 Mar 2023 18:20:13 +0000 | From | Cristian Marussi <> | Subject | Re: Circular lockdep in kvm_reset_vcpu() ? |
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On Mon, Mar 13, 2023 at 02:09:55PM +0000, Marc Zyngier wrote: > On 2023-03-13 10:09, Cristian Marussi wrote: > > On Sat, Feb 11, 2023 at 12:56:41AM +0000, Oliver Upton wrote: > > > Hi Jeremy, > > > > > > > Hi, > > > > > On Fri, Feb 10, 2023 at 11:46:36AM -0600, Jeremy Linton wrote: > > > > Hi, > > > > > > > > I saw this pop yesterday: > > > > > > You and me both actually! Shame on me, I spoke off-list about this > > > with > > > Marc in passing. Thanks for sending along the report. > > > > > > > [ 78.333360] ====================================================== > > > > [ 78.339541] WARNING: possible circular locking dependency detected > > > > [ 78.345721] 6.2.0-rc7+ #19 Not tainted > > > > [ 78.349470] ------------------------------------------------------ > > > > [ 78.355647] qemu-system-aar/859 is trying to acquire lock: > > > > [ 78.361130] ffff5aa69269eba0 (&host_kvm->lock){+.+.}-{3:3}, at: > > > > kvm_reset_vcpu+0x34/0x274 > > > > [ 78.369344] > > > > [ 78.369344] but task is already holding lock: > > > > [ 78.375182] ffff5aa68768c0b8 (&vcpu->mutex){+.+.}-{3:3}, at: > > > > kvm_vcpu_ioctl+0x8c/0xba0 > > > > > > [...] > > > > > > > It appears to be triggered by the new commit 42a90008f890a ('KVM: Ensure > > > > lockdep knows about kvm->lock vs. vcpu->mutex ordering rule') which is > > > > detecting the vcpu lock grabbed by kvm_vcpu_ioctl() and then the kvm mutext > > > > grabbed by kvm_reset_vcpu(). > > > > > > Right, this commit gave lockdep what it needed to smack us on the head > > > for getting the locking wrong in the arm64 side. > > > > > > As gross as it might be, the right direction is likely to have our own > > > lock in kvm_arch that we can acquire while holding the vcpu mutex. > > > I'll > > > throw a patch at the list once I get done testing it. > > > > > > > I just hit this using a v6.3-rc2 and a mainline kvmtool. > > > > In my case, though, the guest does not even boot if I use more than 1 > > vcpu, which > > I suppose triggers effectively the reported possible deadlock, i.e.: > > > > root/lkvm_master run -c 4 -m 4096 -k /root/Image_guest -d > > /root/disk_debian_buster_guest.img -p "loglevel=8" > > # lkvm run -k /root/Image_guest -m 4096 -c 4 --name guest-288 > > ....<HANGS FOREVER> > > Pass earlycon to the guest for a start. > > I seriously doubt someone has actually seen a deadlock, because > the issue has been there for at least the past 7 years... > > And -rc2 works just fine here.
Thanks, I'll dig deeper what's going on un my setup. Cristian
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