[PATCH] mm: page fault handlers tidyup

Impose a little more consistency on the page fault handlers do_wp_page,
do_swap_page, do_anonymous_page, do_no_page, do_file_page: why not pass their
arguments in the same order, called the same names?

break_cow is all very well, but what it did was inlined elsewhere: easier to
compare if it's brought back into do_wp_page.

do_file_page's fallback to do_no_page dates from a time when we were testing
pte_file by using it wherever possible: currently it's peculiar to nonlinear
vmas, so just check that.  BUG_ON if not?  Better not, it's probably page
table corruption, so just show the pte: hmm, there's a pte_ERROR macro, let's
use that for do_wp_page's invalid pfn too.

Hah!  Someone in the ppc64 world noticed pte_ERROR was unused so removed it:
restored (and say "pud" not "pmd" in its pud_ERROR).

Signed-off-by: Hugh Dickins <hugh@veritas.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

3 files changed, 99 insertions, 125 deletions

diff --git a/mm/filemap.c b/mm/filemap.c
index 1c31b2fd2ca5..8aa344e88489 100644
--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -1520,7 +1520,7 @@ repeat:
                         page_cache_release(page);
                         return err;
                 }
-        } else {
+        } else if (vma->vm_flags & VM_NONLINEAR) {
                 /* No page was found just because we can't read it in now (being
                  * here implies nonblock != 0), but the page may exist, so set
                  * the PTE to fault it in later. */
diff --git a/mm/memory.c b/mm/memory.c
index 13667681cd16..eaf79031f573 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -1213,28 +1213,10 @@ static inline pte_t maybe_mkwrite(pte_t pte, struct vm_area_struct *vma)
 }
 
 /*
- * We hold the mm semaphore for reading and vma->vm_mm->page_table_lock
- */
-static inline void break_cow(struct vm_area_struct * vma, struct page * new_page, unsigned long address, 
-                pte_t *page_table)
-{
-        pte_t entry;
-
-        entry = maybe_mkwrite(pte_mkdirty(mk_pte(new_page, vma->vm_page_prot)),
-                              vma);
-        ptep_establish(vma, address, page_table, entry);
-        update_mmu_cache(vma, address, entry);
-        lazy_mmu_prot_update(entry);
-}
-
-/*
  * This routine handles present pages, when users try to write
  * to a shared page. It is done by copying the page to a new address
  * and decrementing the shared-page counter for the old page.
  *
- * Goto-purists beware: the only reason for goto's here is that it results
- * in better assembly code.. The "default" path will see no jumps at all.
- *
  * Note that this routine assumes that the protection checks have been
  * done by the caller (the low-level page fault routine in most cases).
  * Thus we can safely just mark it writable once we've done any necessary
@@ -1247,25 +1229,22 @@ static inline void break_cow(struct vm_area_struct * vma, struct page * new_page
  * We hold the mm semaphore and the page_table_lock on entry and exit
  * with the page_table_lock released.
  */
-static int do_wp_page(struct mm_struct *mm, struct vm_area_struct * vma,
-        unsigned long address, pte_t *page_table, pmd_t *pmd, pte_t pte)
+static int do_wp_page(struct mm_struct *mm, struct vm_area_struct *vma,
+                unsigned long address, pte_t *page_table, pmd_t *pmd,
+                pte_t orig_pte)
 {
         struct page *old_page, *new_page;
-        unsigned long pfn = pte_pfn(pte);
+        unsigned long pfn = pte_pfn(orig_pte);
         pte_t entry;
-        int ret;
+        int ret = VM_FAULT_MINOR;
 
         if (unlikely(!pfn_valid(pfn))) {
                 /*
-                 * This should really halt the system so it can be debugged or
-                 * at least the kernel stops what it's doing before it corrupts
-                 * data, but for the moment just pretend this is OOM.
+                 * Page table corrupted: show pte and kill process.
                  */
-                pte_unmap(page_table);
-                printk(KERN_ERR "do_wp_page: bogus page at address %08lx\n",
-                                address);
-                spin_unlock(&mm->page_table_lock);
-                return VM_FAULT_OOM;
+                pte_ERROR(orig_pte);
+                ret = VM_FAULT_OOM;
+                goto unlock;
         }
         old_page = pfn_to_page(pfn);
 
@@ -1274,52 +1253,57 @@ static int do_wp_page(struct mm_struct *mm, struct vm_area_struct * vma,
                 unlock_page(old_page);
                 if (reuse) {
                         flush_cache_page(vma, address, pfn);
-                        entry = maybe_mkwrite(pte_mkyoung(pte_mkdirty(pte)),
-                                              vma);
+                        entry = pte_mkyoung(orig_pte);
+                        entry = maybe_mkwrite(pte_mkdirty(entry), vma);
                         ptep_set_access_flags(vma, address, page_table, entry, 1);
                         update_mmu_cache(vma, address, entry);
                         lazy_mmu_prot_update(entry);
-                        pte_unmap(page_table);
-                        spin_unlock(&mm->page_table_lock);
-                        return VM_FAULT_MINOR|VM_FAULT_WRITE;
+                        ret |= VM_FAULT_WRITE;
+                        goto unlock;
                 }
         }
-        pte_unmap(page_table);
 
         /*
          * Ok, we need to copy. Oh, well..
          */
         if (!PageReserved(old_page))
                 page_cache_get(old_page);
+        pte_unmap(page_table);
         spin_unlock(&mm->page_table_lock);
 
         if (unlikely(anon_vma_prepare(vma)))
-                goto no_new_page;
+                goto oom;
         if (old_page == ZERO_PAGE(address)) {
                 new_page = alloc_zeroed_user_highpage(vma, address);
                 if (!new_page)
-                        goto no_new_page;
+                        goto oom;
         } else {
                 new_page = alloc_page_vma(GFP_HIGHUSER, vma, address);
                 if (!new_page)
-                        goto no_new_page;
+                        goto oom;
                 copy_user_highpage(new_page, old_page, address);
         }
+
         /*
          * Re-check the pte - we dropped the lock
          */
-        ret = VM_FAULT_MINOR;
         spin_lock(&mm->page_table_lock);
         page_table = pte_offset_map(pmd, address);
-        if (likely(pte_same(*page_table, pte))) {
+        if (likely(pte_same(*page_table, orig_pte))) {
                 if (PageAnon(old_page))
                         dec_mm_counter(mm, anon_rss);
                 if (PageReserved(old_page))
                         inc_mm_counter(mm, rss);
                 else
                         page_remove_rmap(old_page);
+
                 flush_cache_page(vma, address, pfn);
-                break_cow(vma, new_page, address, page_table);
+                entry = mk_pte(new_page, vma->vm_page_prot);
+                entry = maybe_mkwrite(pte_mkdirty(entry), vma);
+                ptep_establish(vma, address, page_table, entry);
+                update_mmu_cache(vma, address, entry);
+                lazy_mmu_prot_update(entry);
+
                 lru_cache_add_active(new_page);
                 page_add_anon_rmap(new_page, vma, address);
 
@@ -1327,13 +1311,13 @@ static int do_wp_page(struct mm_struct *mm, struct vm_area_struct * vma,
                 new_page = old_page;
                 ret |= VM_FAULT_WRITE;
         }
-        pte_unmap(page_table);
         page_cache_release(new_page);
         page_cache_release(old_page);
+unlock:
+        pte_unmap(page_table);
         spin_unlock(&mm->page_table_lock);
         return ret;
-
-no_new_page:
+oom:
         page_cache_release(old_page);
         return VM_FAULT_OOM;
 }
@@ -1661,17 +1645,19 @@ void swapin_readahead(swp_entry_t entry, unsigned long addr,struct vm_area_struc
  * We hold the mm semaphore and the page_table_lock on entry and
  * should release the pagetable lock on exit..
  */
-static int do_swap_page(struct mm_struct * mm,
-        struct vm_area_struct * vma, unsigned long address,
-        pte_t *page_table, pmd_t *pmd, pte_t orig_pte, int write_access)
+static int do_swap_page(struct mm_struct *mm, struct vm_area_struct *vma,
+                unsigned long address, pte_t *page_table, pmd_t *pmd,
+                int write_access, pte_t orig_pte)
 {
         struct page *page;
-        swp_entry_t entry = pte_to_swp_entry(orig_pte);
+        swp_entry_t entry;
         pte_t pte;
         int ret = VM_FAULT_MINOR;
 
         pte_unmap(page_table);
         spin_unlock(&mm->page_table_lock);
+
+        entry = pte_to_swp_entry(orig_pte);
         page = lookup_swap_cache(entry);
         if (!page) {
                 swapin_readahead(entry, address, vma);
@@ -1685,11 +1671,7 @@ static int do_swap_page(struct mm_struct * mm,
                         page_table = pte_offset_map(pmd, address);
                         if (likely(pte_same(*page_table, orig_pte)))
                                 ret = VM_FAULT_OOM;
-                        else
-                                ret = VM_FAULT_MINOR;
-                        pte_unmap(page_table);
-                        spin_unlock(&mm->page_table_lock);
-                        goto out;
+                        goto unlock;
                 }
 
                 /* Had to read the page from swap area: Major fault */
@@ -1745,6 +1727,7 @@ static int do_swap_page(struct mm_struct * mm,
         /* No need to invalidate - it was non-present before */
         update_mmu_cache(vma, address, pte);
         lazy_mmu_prot_update(pte);
+unlock:
         pte_unmap(page_table);
         spin_unlock(&mm->page_table_lock);
 out:
@@ -1754,7 +1737,7 @@ out_nomap:
         spin_unlock(&mm->page_table_lock);
         unlock_page(page);
         page_cache_release(page);
-        goto out;
+        return ret;
 }
 
 /*
@@ -1762,17 +1745,15 @@ out_nomap:
  * spinlock held to protect against concurrent faults in
  * multithreaded programs. 
  */
-static int
-do_anonymous_page(struct mm_struct *mm, struct vm_area_struct *vma,
-                pte_t *page_table, pmd_t *pmd, int write_access,
-                unsigned long addr)
+static int do_anonymous_page(struct mm_struct *mm, struct vm_area_struct *vma,
+                unsigned long address, pte_t *page_table, pmd_t *pmd,
+                int write_access)
 {
         pte_t entry;
 
         /* Mapping of ZERO_PAGE - vm_page_prot is readonly */
         entry = mk_pte(ZERO_PAGE(addr), vma->vm_page_prot);
 
-        /* ..except if it's a write access */
         if (write_access) {
                 struct page *page;
 
@@ -1781,39 +1762,36 @@ do_anonymous_page(struct mm_struct *mm, struct vm_area_struct *vma,
                 spin_unlock(&mm->page_table_lock);
 
                 if (unlikely(anon_vma_prepare(vma)))
-                        goto no_mem;
-                page = alloc_zeroed_user_highpage(vma, addr);
+                        goto oom;
+                page = alloc_zeroed_user_highpage(vma, address);
                 if (!page)
-                        goto no_mem;
+                        goto oom;
 
                 spin_lock(&mm->page_table_lock);
-                page_table = pte_offset_map(pmd, addr);
+                page_table = pte_offset_map(pmd, address);
 
                 if (!pte_none(*page_table)) {
-                        pte_unmap(page_table);
                         page_cache_release(page);
-                        spin_unlock(&mm->page_table_lock);
-                        goto out;
+                        goto unlock;
                 }
                 inc_mm_counter(mm, rss);
-                entry = maybe_mkwrite(pte_mkdirty(mk_pte(page,
-                                                         vma->vm_page_prot)),
-                                      vma);
+                entry = mk_pte(page, vma->vm_page_prot);
+                entry = maybe_mkwrite(pte_mkdirty(entry), vma);
                 lru_cache_add_active(page);
                 SetPageReferenced(page);
-                page_add_anon_rmap(page, vma, addr);
+                page_add_anon_rmap(page, vma, address);
         }
 
-        set_pte_at(mm, addr, page_table, entry);
-        pte_unmap(page_table);
+        set_pte_at(mm, address, page_table, entry);
 
         /* No need to invalidate - it was non-present before */
-        update_mmu_cache(vma, addr, entry);
+        update_mmu_cache(vma, address, entry);
         lazy_mmu_prot_update(entry);
+unlock:
+        pte_unmap(page_table);
         spin_unlock(&mm->page_table_lock);
-out:
         return VM_FAULT_MINOR;
-no_mem:
+oom:
         return VM_FAULT_OOM;
 }
 
@@ -1829,20 +1807,17 @@ no_mem:
  * This is called with the MM semaphore held and the page table
  * spinlock held. Exit with the spinlock released.
  */
-static int
-do_no_page(struct mm_struct *mm, struct vm_area_struct *vma,
-        unsigned long address, int write_access, pte_t *page_table, pmd_t *pmd)
+static int do_no_page(struct mm_struct *mm, struct vm_area_struct *vma,
+                unsigned long address, pte_t *page_table, pmd_t *pmd,
+                int write_access)
 {
-        struct page * new_page;
+        struct page *new_page;
         struct address_space *mapping = NULL;
         pte_t entry;
         unsigned int sequence = 0;
         int ret = VM_FAULT_MINOR;
         int anon = 0;
 
-        if (!vma->vm_ops || !vma->vm_ops->nopage)
-                return do_anonymous_page(mm, vma, page_table,
-                                        pmd, write_access, address);
         pte_unmap(page_table);
         spin_unlock(&mm->page_table_lock);
 
@@ -1852,7 +1827,6 @@ do_no_page(struct mm_struct *mm, struct vm_area_struct *vma,
                 smp_rmb(); /* serializes i_size against truncate_count */
         }
 retry:
-        cond_resched();
         new_page = vma->vm_ops->nopage(vma, address & PAGE_MASK, &ret);
         /*
          * No smp_rmb is needed here as long as there's a full
@@ -1892,9 +1866,11 @@ retry:
          * retry getting the page.
          */
         if (mapping && unlikely(sequence != mapping->truncate_count)) {
-                sequence = mapping->truncate_count;
                 spin_unlock(&mm->page_table_lock);
                 page_cache_release(new_page);
+                cond_resched();
+                sequence = mapping->truncate_count;
+                smp_rmb();
                 goto retry;
         }
         page_table = pte_offset_map(pmd, address);
@@ -1924,25 +1900,22 @@ retry:
                         page_add_anon_rmap(new_page, vma, address);
                 } else
                         page_add_file_rmap(new_page);
-                pte_unmap(page_table);
         } else {
                 /* One of our sibling threads was faster, back out. */
-                pte_unmap(page_table);
                 page_cache_release(new_page);
-                spin_unlock(&mm->page_table_lock);
-                goto out;
+                goto unlock;
         }
 
         /* no need to invalidate: a not-present page shouldn't be cached */
         update_mmu_cache(vma, address, entry);
         lazy_mmu_prot_update(entry);
+unlock:
+        pte_unmap(page_table);
         spin_unlock(&mm->page_table_lock);
-out:
         return ret;
 oom:
         page_cache_release(new_page);
-        ret = VM_FAULT_OOM;
-        goto out;
+        return VM_FAULT_OOM;
 }
 
 /*
@@ -1950,29 +1923,28 @@ oom:
  * from the encoded file_pte if possible. This enables swappable
  * nonlinear vmas.
  */
-static int do_file_page(struct mm_struct * mm, struct vm_area_struct * vma,
-        unsigned long address, int write_access, pte_t *pte, pmd_t *pmd)
+static int do_file_page(struct mm_struct *mm, struct vm_area_struct *vma,
+                unsigned long address, pte_t *page_table, pmd_t *pmd,
+                int write_access, pte_t orig_pte)
 {
-        unsigned long pgoff;
+        pgoff_t pgoff;
         int err;
 
-        BUG_ON(!vma->vm_ops || !vma->vm_ops->nopage);
-        /*
-         * Fall back to the linear mapping if the fs does not support
-         * ->populate:
-         */
-        if (!vma->vm_ops->populate ||
-                        (write_access && !(vma->vm_flags & VM_SHARED))) {
-                pte_clear(mm, address, pte);
-                return do_no_page(mm, vma, address, write_access, pte, pmd);
-        }
-
-        pgoff = pte_to_pgoff(*pte);
-
-        pte_unmap(pte);
+        pte_unmap(page_table);
         spin_unlock(&mm->page_table_lock);
 
-        err = vma->vm_ops->populate(vma, address & PAGE_MASK, PAGE_SIZE, vma->vm_page_prot, pgoff, 0);
+        if (unlikely(!(vma->vm_flags & VM_NONLINEAR))) {
+                /*
+                 * Page table corrupted: show pte and kill process.
+                 */
+                pte_ERROR(orig_pte);
+                return VM_FAULT_OOM;
+        }
+        /* We can then assume vm->vm_ops && vma->vm_ops->populate */
+
+        pgoff = pte_to_pgoff(orig_pte);
+        err = vma->vm_ops->populate(vma, address & PAGE_MASK, PAGE_SIZE,
+                                        vma->vm_page_prot, pgoff, 0);
         if (err == -ENOMEM)
                 return VM_FAULT_OOM;
         if (err)
@@ -2002,23 +1974,25 @@ static int do_file_page(struct mm_struct * mm, struct vm_area_struct * vma,
  * release it when done.
  */
 static inline int handle_pte_fault(struct mm_struct *mm,
-        struct vm_area_struct * vma, unsigned long address,
-        int write_access, pte_t *pte, pmd_t *pmd)
+                struct vm_area_struct *vma, unsigned long address,
+                pte_t *pte, pmd_t *pmd, int write_access)
 {
         pte_t entry;
 
         entry = *pte;
         if (!pte_present(entry)) {
-                /*
-                 * If it truly wasn't present, we know that kswapd
-                 * and the PTE updates will not touch it later. So
-                 * drop the lock.
-                 */
-                if (pte_none(entry))
-                        return do_no_page(mm, vma, address, write_access, pte, pmd);
+                if (pte_none(entry)) {
+                        if (!vma->vm_ops || !vma->vm_ops->nopage)
+                                return do_anonymous_page(mm, vma, address,
+                                        pte, pmd, write_access);
+                        return do_no_page(mm, vma, address,
+                                        pte, pmd, write_access);
+                }
                 if (pte_file(entry))
-                        return do_file_page(mm, vma, address, write_access, pte, pmd);
-                return do_swap_page(mm, vma, address, pte, pmd, entry, write_access);
+                        return do_file_page(mm, vma, address,
+                                        pte, pmd, write_access, entry);
+                return do_swap_page(mm, vma, address,
+                                        pte, pmd, write_access, entry);
         }
 
         if (write_access) {
@@ -2038,7 +2012,7 @@ static inline int handle_pte_fault(struct mm_struct *mm,
 /*
  * By the time we get here, we already hold the mm semaphore
  */
-int __handle_mm_fault(struct mm_struct *mm, struct vm_area_struct * vma,
+int __handle_mm_fault(struct mm_struct *mm, struct vm_area_struct *vma,
                 unsigned long address, int write_access)
 {
         pgd_t *pgd;
@@ -2072,7 +2046,7 @@ int __handle_mm_fault(struct mm_struct *mm, struct vm_area_struct * vma,
         if (!pte)
                 goto oom;
         
-        return handle_pte_fault(mm, vma, address, write_access, pte, pmd);
+        return handle_pte_fault(mm, vma, address, pte, pmd, write_access);
 
  oom:
         spin_unlock(&mm->page_table_lock);
diff --git a/mm/shmem.c b/mm/shmem.c
index 55e04a0734c1..6796311a23ef 100644
--- a/mm/shmem.c
+++ b/mm/shmem.c
@@ -1201,7 +1201,7 @@ static int shmem_populate(struct vm_area_struct *vma,
                                 page_cache_release(page);
                                 return err;
                         }
-                } else {
+                } else if (vma->vm_flags & VM_NONLINEAR) {
                         /* No page was found just because we can't read it in
                          * now (being here implies nonblock != 0), but the page
                          * may exist, so set the PTE to fault it in later. */