On 04/11/19 07:27, Wanpeng Li wrote:
> From: Wanpeng Li <wanpengli@xxxxxxxxxxx>
>
> Reported by syzkaller:
>
> =============================
> WARNING: suspicious RCU usage
> -----------------------------
> ./include/linux/kvm_host.h:536 suspicious rcu_dereference_check() usage!
>
> other info that might help us debug this:
>
> rcu_scheduler_active = 2, debug_locks = 1
> no locks held by repro_11/12688.
>
> stack backtrace:
> Call Trace:
> dump_stack+0x7d/0xc5
> lockdep_rcu_suspicious+0x123/0x170
> kvm_dev_ioctl+0x9a9/0x1260 [kvm]
> do_vfs_ioctl+0x1a1/0xfb0
> ksys_ioctl+0x6d/0x80
> __x64_sys_ioctl+0x73/0xb0
> do_syscall_64+0x108/0xaa0
> entry_SYSCALL_64_after_hwframe+0x49/0xbe
>
> Commit a97b0e773e4 (kvm: call kvm_arch_destroy_vm if vm creation fails)
> sets users_count to 1 before kvm_arch_init_vm(), however, if kvm_arch_init_vm()
> fails, we need to dec this count. Or, we can move the sets refcount after
> kvm_arch_init_vm().
I don't understand this one, hasn't
WARN_ON_ONCE(!refcount_dec_and_test(&kvm->users_count));
decreased the conut already? With your patch the refcount would then
underflow.
Paolo
