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mm: change return values of finish_mkwrite_fault()

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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>
This commit is contained in:
Jan Kara 2016-12-14 15:07:42 -08:00 committed by Linus Torvalds
parent 66a6197c11
commit a19e25536e
1 changed files with 3 additions and 4 deletions
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7
mm/memory.c
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@ -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;