[PATCH] MIPS: Add FAULT_FLAG_ALLOW_RETRY in page fault handler

[Hillf Danton <dhillf@gmail.com>]

The flag, FAULT_FLAG_ALLOW_RETRY, was introduced by the patch,

        mm: retry page fault when blocking on disk transfer
        commit: d065bd810b6deb67d4897a14bfe21f8eb526ba99

for reducing mmap_sem hold times that are caused by waiting for disk
transfers when accessing file mapped VMAs. So add it now.

Signed-off-by: Hillf Danton <dhillf@gmail.com>
---

--- a/arch/mips/mm/fault.c      Fri Nov 18 22:23:40 2011
+++ b/arch/mips/mm/fault.c      Fri Nov 18 22:36:04 2011
@@ -42,6 +42,8 @@ asmlinkage void __kprobes do_page_fault(
        const int field = sizeof(unsigned long) * 2;
        siginfo_t info;
        int fault;
+       unsigned int flags = FAULT_FLAG_ALLOW_RETRY |
+                               (write ? FAULT_FLAG_WRITE : 0);

 #if 0
        printk("Cpu%d[%s:%d:%0*lx:%ld:%0*lx]\n", raw_smp_processor_id(),
@@ -91,6 +93,7 @@ asmlinkage void __kprobes do_page_fault(
        if (in_atomic() || !mm)
                goto bad_area_nosemaphore;

+retry:
        down_read(&mm->mmap_sem);
        vma = find_vma(mm, address);
        if (!vma)
@@ -144,7 +147,7 @@ good_area:
         * make sure we exit gracefully rather than endlessly redo
         * the fault.
         */
-       fault = handle_mm_fault(mm, vma, address, write ? FAULT_FLAG_WRITE : 0);
+       fault = handle_mm_fault(mm, vma, address, flags);
        perf_sw_event(PERF_COUNT_SW_PAGE_FAULTS, 1, regs, address);
        if (unlikely(fault & VM_FAULT_ERROR)) {
                if (fault & VM_FAULT_OOM)
@@ -152,6 +155,12 @@ good_area:
                else if (fault & VM_FAULT_SIGBUS)
                        goto do_sigbus;
                BUG();
+       }
+       if (flags & FAULT_FLAG_ALLOW_RETRY) {
+               if (fault & VM_FAULT_RETRY) {
+                       flags &= ~FAULT_FLAG_ALLOW_RETRY;
+                       goto retry;
+               }
        }
        if (fault & VM_FAULT_MAJOR) {
                perf_sw_event(PERF_COUNT_SW_PAGE_FAULTS_MAJ, 1, regs, address);