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commit3898da947b("KVM: avoid using rcu_dereference_protected") can trigger the following lockdep/rcu splat if the VM_CREATE ioctl fails, for example if kvm_arch_init_vm fails: WARNING: suspicious RCU usage 4.13.0+ #105 Not tainted ----------------------------- ./include/linux/kvm_host.h:481 suspicious rcu_dereference_check() usage! other info that might help us debug this: rcu_scheduler_active = 2, debug_locks = 1 no locks held by qemu-system-s39/79. stack backtrace: CPU: 0 PID: 79 Comm: qemu-system-s39 Not tainted 4.13.0+ #105 Hardware name: IBM 2964 NC9 704 (KVM/Linux) Call Trace: ([<00000000001140b2>] show_stack+0xea/0xf0) [<00000000008a68a4>] dump_stack+0x94/0xd8 [<0000000000134c12>] kvm_dev_ioctl+0x372/0x7a0 [<000000000038f940>] do_vfs_ioctl+0xa8/0x6c8 [<0000000000390004>] SyS_ioctl+0xa4/0xb8 [<00000000008c7a8c>] system_call+0xc4/0x27c no locks held by qemu-system-s39/79. We have to reset the just created users_count back to 0 to tell the check to not trigger. Reported-by: Stefan Haberland <sth@linux.vnet.ibm.com> Signed-off-by: Christian Borntraeger <borntraeger@de.ibm.com> Fixes:3898da947b("KVM: avoid using rcu_dereference_protected") Cc: Paolo Bonzini <pbonzini@redhat.com> Reviewed-by: David Hildenbrand <david@redhat.com> Signed-off-by: Radim Krčmář <rkrcmar@redhat.com>
Linux kernel ============ This file was moved to Documentation/admin-guide/README.rst Please notice that there are several guides for kernel developers and users. These guides can be rendered in a number of formats, like HTML and PDF. In order to build the documentation, use ``make htmldocs`` or ``make pdfdocs``. There are various text files in the Documentation/ subdirectory, several of them using the Restructured Text markup notation. See Documentation/00-INDEX for a list of what is contained in each file. Please read the Documentation/process/changes.rst file, as it contains the requirements for building and running the kernel, and information about the problems which may result by upgrading your kernel.