Hi,
I've got a warning with the latest Linus tree like below:
[ INFO: suspicious RCU usage. ]
3.18.0-rc2-test2+ #70 Not tainted
-------------------------------
include/linux/kvm_host.h:474 suspicious rcu_dereference_check() usage!
other info that might help us debug this:
rcu_scheduler_active = 1, debug_locks = 0
1 lock held by qemu-system-x86/2371:
#0: (&vcpu->mutex){+.+...}, at: [<ffffffffa037d800>] vcpu_load+0x20/0xd0 [kvm]
stack backtrace:
CPU: 4 PID: 2371 Comm: qemu-system-x86 Not tainted 3.18.0-rc2-test2+ #70
Hardware name: Dell Inc. OptiPlex 9010/0M9KCM, BIOS A12 01/10/2013
0000000000000001 ffff880209983ca8 ffffffff816f514f 0000000000000000
ffff8802099b8990 ffff880209983cd8 ffffffff810bd687 00000000000fee00
ffff880208a2c000 ffff880208a10000 ffff88020ef50040 ffff880209983d08
Call Trace:
[<ffffffff816f514f>] dump_stack+0x4e/0x71
[<ffffffff810bd687>] lockdep_rcu_suspicious+0xe7/0x120
[<ffffffffa037d055>] gfn_to_memslot+0xd5/0xe0 [kvm]
[<ffffffffa03807d3>] __gfn_to_pfn+0x33/0x60 [kvm]
[<ffffffffa0380885>] gfn_to_page+0x25/0x90 [kvm]
[<ffffffffa038aeec>] kvm_vcpu_reload_apic_access_page+0x3c/0x80 [kvm]
[<ffffffffa08f0a9c>] vmx_vcpu_reset+0x20c/0x460 [kvm_intel]
[<ffffffffa039ab8e>] kvm_vcpu_reset+0x15e/0x1b0 [kvm]
[<ffffffffa039ac0c>] kvm_arch_vcpu_setup+0x2c/0x50 [kvm]
[<ffffffffa037f7e0>] kvm_vm_ioctl+0x1d0/0x780 [kvm]
[<ffffffff810bc664>] ? __lock_is_held+0x54/0x80
[<ffffffff812231f0>] do_vfs_ioctl+0x300/0x520
[<ffffffff8122ee45>] ? __fget+0x5/0x250
[<ffffffff8122f0fa>] ? __fget_light+0x2a/0xe0
[<ffffffff81223491>] SyS_ioctl+0x81/0xa0
[<ffffffff816fed6d>] system_call_fastpath+0x16/0x1b
kvm: zapping shadow pages for mmio generation wraparound
kvm [2369]: vcpu0 disabled perfctr wrmsr: 0xc1 data 0xffff
The machine itself and KVM work fine even after this warning. I'm not
sure whether this is new, maybe it's triggered now since I changed my
Kconfig to cover more RCU testing recently. The warning is
reproducible, I can see it at the first invocation of kvm after each
fresh boot.
Does this ring a bell to anyone?
thanks,
Takashi
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