Commit a19e2553 authored Dec 14, 2016 by Jan Kara Committed by Linus Torvalds Dec 14, 2016

mm: change return values of finish_mkwrite_fault()

Currently finish_mkwrite_fault() returns 0 when PTE got changed before
we acquired PTE lock and VM_FAULT_WRITE when we succeeded in modifying
the PTE. This is somewhat confusing since 0 generally means success, it
is also inconsistent with finish_fault() which returns 0 on success.
Change finish_mkwrite_fault() to return 0 on success and VM_FAULT_NOPAGE
when PTE changed. Practically, there should be no behavioral difference
since we bail out from the fault the same way regardless whether we
return 0, VM_FAULT_NOPAGE, or VM_FAULT_WRITE. Also note that
VM_FAULT_WRITE has no effect for shared mappings since the only two
places that check it - KSM and GUP - care about private mappings only.
Generally the meaning of VM_FAULT_WRITE for shared mappings is not well
defined and we should probably clean that up.

Link: http://lkml.kernel.org/r/1479460644-25076-17-git-send-email-jack@suse.cz

Signed-off-by: Jan Kara <jack@suse.cz>
Acked-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Cc: Ross Zwisler <ross.zwisler@linux.intel.com>
Cc: Dan Williams <dan.j.williams@intel.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

parent 66a6197c

mm/memory.c

+3 −4

Original line number	Diff line number	Diff line
		@@ -2295,10 +2295,10 @@ int finish_mkwrite_fault(struct vm_fault *vmf)
		*/
		if (!pte_same(*vmf->pte, vmf->orig_pte)) {
		pte_unmap_unlock(vmf->pte, vmf->ptl);
		return 0;
		return VM_FAULT_NOPAGE;
		}
		wp_page_reuse(vmf);
		return VM_FAULT_WRITE;
		return 0;
		}

		/*
		@@ -2341,8 +2341,7 @@ static int wp_page_shared(struct vm_fault *vmf)
		return tmp;
		}
		tmp = finish_mkwrite_fault(vmf);
		if (unlikely(!tmp \|\| (tmp &
		(VM_FAULT_ERROR \| VM_FAULT_NOPAGE)))) {
		if (unlikely(tmp & (VM_FAULT_ERROR \| VM_FAULT_NOPAGE))) {
		unlock_page(vmf->page);
		put_page(vmf->page);
		return tmp;