mm: extract code to fault in a page from __get_user_pages()
Nesting level in __get_user_pages() is just insane. Let's try to fix it
a bit.
Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
diff --git a/mm/gup.c b/mm/gup.c
index 4063678..28e3700 100644
--- a/mm/gup.c
+++ b/mm/gup.c
@@ -214,12 +214,6 @@
return follow_page_pte(vma, address, pmd, flags);
}
-static inline int stack_guard_page(struct vm_area_struct *vma, unsigned long addr)
-{
- return stack_guard_page_start(vma, addr) ||
- stack_guard_page_end(vma, addr+PAGE_SIZE);
-}
-
static int get_gate_page(struct mm_struct *mm, unsigned long address,
unsigned int gup_flags, struct vm_area_struct **vma,
struct page **page)
@@ -264,6 +258,63 @@
return ret;
}
+static int faultin_page(struct task_struct *tsk, struct vm_area_struct *vma,
+ unsigned long address, unsigned int *flags, int *nonblocking)
+{
+ struct mm_struct *mm = vma->vm_mm;
+ unsigned int fault_flags = 0;
+ int ret;
+
+ /* For mlock, just skip the stack guard page. */
+ if ((*flags & FOLL_MLOCK) &&
+ (stack_guard_page_start(vma, address) ||
+ stack_guard_page_end(vma, address + PAGE_SIZE)))
+ return -ENOENT;
+ if (*flags & FOLL_WRITE)
+ fault_flags |= FAULT_FLAG_WRITE;
+ if (nonblocking)
+ fault_flags |= FAULT_FLAG_ALLOW_RETRY;
+ if (*flags & FOLL_NOWAIT)
+ fault_flags |= FAULT_FLAG_ALLOW_RETRY | FAULT_FLAG_RETRY_NOWAIT;
+
+ ret = handle_mm_fault(mm, vma, address, fault_flags);
+ if (ret & VM_FAULT_ERROR) {
+ if (ret & VM_FAULT_OOM)
+ return -ENOMEM;
+ if (ret & (VM_FAULT_HWPOISON | VM_FAULT_HWPOISON_LARGE))
+ return *flags & FOLL_HWPOISON ? -EHWPOISON : -EFAULT;
+ if (ret & VM_FAULT_SIGBUS)
+ return -EFAULT;
+ BUG();
+ }
+
+ if (tsk) {
+ if (ret & VM_FAULT_MAJOR)
+ tsk->maj_flt++;
+ else
+ tsk->min_flt++;
+ }
+
+ if (ret & VM_FAULT_RETRY) {
+ if (nonblocking)
+ *nonblocking = 0;
+ return -EBUSY;
+ }
+
+ /*
+ * The VM_FAULT_WRITE bit tells us that do_wp_page has broken COW when
+ * necessary, even if maybe_mkwrite decided not to set pte_write. We
+ * can thus safely do subsequent page lookups as if they were reads.
+ * But only do so when looping for pte_write is futile: in some cases
+ * userspace may also be wanting to write to the gotten user page,
+ * which a read fault here might prevent (a readonly page might get
+ * reCOWed by userspace write).
+ */
+ if ((ret & VM_FAULT_WRITE) && !(vma->vm_flags & VM_WRITE))
+ *flags &= ~FOLL_WRITE;
+ return 0;
+}
+
/**
* __get_user_pages() - pin user pages in memory
* @tsk: task_struct of target task
@@ -410,69 +461,22 @@
while (!(page = follow_page_mask(vma, start,
foll_flags, &page_mask))) {
int ret;
- unsigned int fault_flags = 0;
-
- /* For mlock, just skip the stack guard page. */
- if (foll_flags & FOLL_MLOCK) {
- if (stack_guard_page(vma, start))
- goto next_page;
- }
- if (foll_flags & FOLL_WRITE)
- fault_flags |= FAULT_FLAG_WRITE;
- if (nonblocking)
- fault_flags |= FAULT_FLAG_ALLOW_RETRY;
- if (foll_flags & FOLL_NOWAIT)
- fault_flags |= (FAULT_FLAG_ALLOW_RETRY | FAULT_FLAG_RETRY_NOWAIT);
-
- ret = handle_mm_fault(mm, vma, start,
- fault_flags);
-
- if (ret & VM_FAULT_ERROR) {
- if (ret & VM_FAULT_OOM)
- return i ? i : -ENOMEM;
- if (ret & (VM_FAULT_HWPOISON |
- VM_FAULT_HWPOISON_LARGE)) {
- if (i)
- return i;
- else if (gup_flags & FOLL_HWPOISON)
- return -EHWPOISON;
- else
- return -EFAULT;
- }
- if (ret & VM_FAULT_SIGBUS)
- goto efault;
+ ret = faultin_page(tsk, vma, start, &foll_flags,
+ nonblocking);
+ switch (ret) {
+ case 0:
+ break;
+ case -EFAULT:
+ case -ENOMEM:
+ case -EHWPOISON:
+ return i ? i : ret;
+ case -EBUSY:
+ return i;
+ case -ENOENT:
+ goto next_page;
+ default:
BUG();
}
-
- if (tsk) {
- if (ret & VM_FAULT_MAJOR)
- tsk->maj_flt++;
- else
- tsk->min_flt++;
- }
-
- if (ret & VM_FAULT_RETRY) {
- if (nonblocking)
- *nonblocking = 0;
- return i;
- }
-
- /*
- * The VM_FAULT_WRITE bit tells us that
- * do_wp_page has broken COW when necessary,
- * even if maybe_mkwrite decided not to set
- * pte_write. We can thus safely do subsequent
- * page lookups as if they were reads. But only
- * do so when looping for pte_write is futile:
- * in some cases userspace may also be wanting
- * to write to the gotten user page, which a
- * read fault here might prevent (a readonly
- * page might get reCOWed by userspace write).
- */
- if ((ret & VM_FAULT_WRITE) &&
- !(vma->vm_flags & VM_WRITE))
- foll_flags &= ~FOLL_WRITE;
-
cond_resched();
}
if (IS_ERR(page))