Thank you for correcting me.
> That's why we can unlock early in the (very common) case of doing an new
> anonymous page: nobody is going to _add_ entries to the page tables
> without holding the mm semaphore, and the anonymous page case doesn't need
> the kernel lock for anything else either.
There seems to be another race: running do_anonymous_page outside the global
lock relies on put_page/set_pte being atomic.
#define set_pte(pteptr, pteval) ((*(pteptr)) = (pteval))
on i386. Nobody gurantees that gcc generates an atomic sequence for this
statement, also it needs a memory barrier to avoid SMP inconsisties.
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