mm->mmap_sem

[James Simmons <jsimmons@edgeglobal.com>]

I noticed that mm_struct has a semaphore in it. How go is it protecting
the memory region? Say we have teh following case. I have a process
that mmaps a chunk of memory and this memory can be sharded with other 
processes. What if the process does a mlock which does a
down(mm->mmap_sem). Now the process goes to sleep and another process
tries to modify the memory region. Will this semaphore protect this
region? In a SMP machine same thing. What kind of protect does this
semaphore provide? Does it prevent other process from doing anything to
the memory. I meant even writing or read it. Thank you.

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