filemap_fault — read in file data for page fault handling
|struct vm_fault * vmf|
filemap_fault is invoked via the vma operations vector for a
mapped memory region to read in file data during a page fault.
The goto's are kind of ugly, but this streamlines the normal case of having it in the page cache, and handles the special cases reasonably without having a lot of duplicated code.
vma->vm_mm->mmap_sem must be held on entry.
If our return value has VM_FAULT_RETRY set, it's because
lock_page_or_retry returned 0.
The mmap_sem has usually been released in this case.
__lock_page_or_retry for the exception.
If our return value does not have VM_FAULT_RETRY set, the mmap_sem has not been released.
We never return with VM_FAULT_RETRY and a bit from VM_FAULT_ERROR set.