xtensa/mm/fault.c: port OOM changes to do_page_fault

Commits d065bd810b6d ("mm: retry page fault when blocking on disk
transfer") and 37b23e0525d3 ("x86,mm: make pagefault killable")
introduced changes into the x86 pagefault handler for making the page
fault handler retryable as well as killable.

These changes reduce the mmap_sem hold time, which is crucial during OOM
killer invocation.

Port these changes to xtensa.

Signed-off-by: Kautuk Consul <consul.kautuk@gmail.com>
Acked-by: Chris Zankel <chris@zankel.net>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 24 insertions, 5 deletions

diff --git a/arch/xtensa/mm/fault.c b/arch/xtensa/mm/fault.c
index b17885a0b508..5a74c53bc69c 100644
--- a/arch/xtensa/mm/fault.c
+++ b/arch/xtensa/mm/fault.c
@@ -44,6 +44,7 @@ void do_page_fault(struct pt_regs *regs)
 
         int is_write, is_exec;
         int fault;
+        unsigned int flags = FAULT_FLAG_ALLOW_RETRY | FAULT_FLAG_KILLABLE;
 
         info.si_code = SEGV_MAPERR;
 
@@ -71,6 +72,7 @@ void do_page_fault(struct pt_regs *regs)
                address, exccause, regs->pc, is_write? "w":"", is_exec? "x":"");
 #endif
 
+retry:
         down_read(&mm->mmap_sem);
         vma = find_vma(mm, address);
 
@@ -93,6 +95,7 @@ good_area:
         if (is_write) {
                 if (!(vma->vm_flags & VM_WRITE))
                         goto bad_area;
+                flags |= FAULT_FLAG_WRITE;
         } else if (is_exec) {
                 if (!(vma->vm_flags & VM_EXEC))
                         goto bad_area;
@@ -104,7 +107,11 @@ good_area:
          * make sure we exit gracefully rather than endlessly redo
          * the fault.
          */
-        fault = handle_mm_fault(mm, vma, address, is_write ? FAULT_FLAG_WRITE : 0);
+        fault = handle_mm_fault(mm, vma, address, flags);
+
+        if ((fault & VM_FAULT_RETRY) && fatal_signal_pending(current))
+                return;
+
         if (unlikely(fault & VM_FAULT_ERROR)) {
                 if (fault & VM_FAULT_OOM)
                         goto out_of_memory;
@@ -112,10 +119,22 @@ good_area:
                         goto do_sigbus;
                 BUG();
         }
-        if (fault & VM_FAULT_MAJOR)
-                current->maj_flt++;
-        else
-                current->min_flt++;
+        if (flags & FAULT_FLAG_ALLOW_RETRY) {
+                if (fault & VM_FAULT_MAJOR)
+                        current->maj_flt++;
+                else
+                        current->min_flt++;
+                if (fault & VM_FAULT_RETRY) {
+                        flags &= ~FAULT_FLAG_ALLOW_RETRY;
+
+                         /* No need to up_read(&mm->mmap_sem) as we would
+                         * have already released it in __lock_page_or_retry
+                         * in mm/filemap.c.
+                         */
+
+                        goto retry;
+                }
+        }
 
         up_read(&mm->mmap_sem);
         return;