Messages in this thread | | | Date | Mon, 13 Mar 2023 14:09:55 +0000 | From | Marc Zyngier <> | Subject | Re: Circular lockdep in kvm_reset_vcpu() ? |
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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.
M. -- Who you jivin' with that Cosmik Debris?
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