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Allow "unlocked" reads of the ram_list by using an RCU-enabled QLIST. The ramlist mutex is kept. call_rcu callbacks are run with the iothread lock taken, but that may change in the future. Writers still take the ramlist mutex, but they no longer need to assume that the iothread lock is taken. Readers of the list, instead, no longer require either the iothread or ramlist mutex, but they need to use rcu_read_lock() and rcu_read_unlock(). One place in arch_init.c was downgrading from write side to read side like this: qemu_mutex_lock_iothread() qemu_mutex_lock_ramlist() ... qemu_mutex_unlock_iothread() ... qemu_mutex_unlock_ramlist() and the equivalent idiom is: qemu_mutex_lock_ramlist() rcu_read_lock() ... qemu_mutex_unlock_ramlist() ... rcu_read_unlock() Reviewed-by: Fam Zheng <famz@redhat.com> Signed-off-by: Mike Day <ncmike@ncultra.org> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
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