Re: [PATCH] kvm: use the correct RCU API

[Avi Kivity <avi@redhat.com>]

On 04/19/2010 12:41 PM, Lai Jiangshan wrote:
> The RCU/SRCU API have already changed for proving RCU usage.
>
> I got the following dmesg when PROVE_RCU=y because we used incorrect API.
> This patch coverts rcu_deference() to srcu_dereference() or family API.
>
> ===================================================
> [ INFO: suspicious rcu_dereference_check() usage. ]
> ---------------------------------------------------
> arch/x86/kvm/mmu.c:3020 invoked rcu_dereference_check() without protection!
>
> other info that might help us debug this:
>
>
> rcu_scheduler_active = 1, debug_locks = 0
> 2 locks held by qemu-system-x86/8550:
>   #0:  (&kvm->slots_lock){+.+.+.}, at: [<ffffffffa011a6ac>] kvm_set_memory_region+0x29/0x50 [kvm]
>   #1:  (&(&kvm->mmu_lock)->rlock){+.+...}, at: [<ffffffffa012262d>] kvm_arch_commit_memory_region+0xa6/0xe2 [kvm]
>
> stack backtrace:
> Pid: 8550, comm: qemu-system-x86 Not tainted 2.6.34-rc4-tip-01028-g939eab1 #27
> Call Trace:
>   [<ffffffff8106c59e>] lockdep_rcu_dereference+0xaa/0xb3
>   [<ffffffffa012f6c1>] kvm_mmu_calculate_mmu_pages+0x44/0x7d [kvm]
>   [<ffffffffa012263e>] kvm_arch_commit_memory_region+0xb7/0xe2 [kvm]
>   [<ffffffffa011a5d7>] __kvm_set_memory_region+0x636/0x6e2 [kvm]
>   [<ffffffffa011a6ba>] kvm_set_memory_region+0x37/0x50 [kvm]
>   [<ffffffffa015e956>] vmx_set_tss_addr+0x46/0x5a [kvm_intel]
>   [<ffffffffa0126592>] kvm_arch_vm_ioctl+0x17a/0xcf8 [kvm]
>   [<ffffffff810a8692>] ? unlock_page+0x27/0x2c
>   [<ffffffff810bf879>] ? __do_fault+0x3a9/0x3e1
>   [<ffffffffa011b12f>] kvm_vm_ioctl+0x364/0x38d [kvm]
>   [<ffffffff81060cfa>] ? up_read+0x23/0x3d
>   [<ffffffff810f3587>] vfs_ioctl+0x32/0xa6
>   [<ffffffff810f3b19>] do_vfs_ioctl+0x495/0x4db
>   [<ffffffff810e6b2f>] ? fget_light+0xc2/0x241
>   [<ffffffff810e416c>] ? do_sys_open+0x104/0x116
>   [<ffffffff81382d6d>] ? retint_swapgs+0xe/0x13
>   [<ffffffff810f3ba6>] sys_ioctl+0x47/0x6a
>   [<ffffffff810021db>] system_call_fastpath+0x16/0x1b
>
>
>
> +static inline struct kvm_memslots *kvm_memslots(struct kvm *kvm)
> +{
> +	return rcu_dereference_check(kvm->memslots,
> +			srcu_read_lock_held(&kvm->srcu)
> +			|| lockdep_is_held(&kvm->slots_lock));
> +}
> +
>    


This open-codes srcu_dereference().  I guess we need an 
srcu_dereference_check().  Paul?

btw, perhaps it is possible not to call rcu_dereference from the write 
paths.


-- 
error compiling committee.c: too many arguments to function