Why do we need both page_table_lock & mmap_sem in the kernel. Why isn't mmap_sem good enough for serialization. As far as i see it, all attempts to change the page table hierarchy in the kernel is done after holding the write lock on mmap_sem. As we are already holding the write lock, we do we need an extra page_table_lock (spinlock) ? Are there any code paths in the kernel which attempt to modify the page table hierarchy without holding the write lock on mmap_sem ?
page_table_lock is a finer grained lock than mmap_sem but page_table_lock is only taken after holding a write lock on mmap_sem (as far as i can tell).
What is the reasoning behind having an extra spinlock?
Thanks.
Venkatram Tummala
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