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.
Signed-off-by: Jan Kara <jack@xxxxxxx>
---
mm/memory.c | 7 +++----
1 file changed, 3 insertions(+), 4 deletions(-)
diff --git a/mm/memory.c b/mm/memory.c
index 1517ff91c743..b3bd6b6c6472 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -2296,10 +2296,10 @@ 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;
}
/*
@@ -2342,8 +2342,7 @@ 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;
--
2.6.6
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