powerpc/mm: Handle VM_FAULT_RETRY earlier

In do_page_fault() if handle_mm_fault() returns VM_FAULT_RETRY, retry
the page fault handling before anything else.

This would simplify the handling of the mmap_sem lock in this part of
the code.

Reviewed-by: Aneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com>
Signed-off-by: Laurent Dufour <ldufour@linux.vnet.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>

diff --git a/arch/powerpc/mm/fault.c b/arch/powerpc/mm/fault.c
index 2d77c1c8014aaa21cceda29cbd62876d5f92bcc1..5809a3c861613dfae486550a9845f82c608f2a21 100644 (file)
--- a/arch/powerpc/mm/fault.c
+++ b/arch/powerpc/mm/fault.c
@@ -458,6 +458,26 @@ good_area:
         * the fault.
         */
        fault = handle_mm_fault(vma, address, flags);
+
+       /*
+        * Handle the retry right now, the mmap_sem has been released in that
+        * case.
+        */
+       if (unlikely(fault & VM_FAULT_RETRY)) {
+               /* We retry only once */
+               if (flags & FAULT_FLAG_ALLOW_RETRY) {
+                       /*
+                        * Clear FAULT_FLAG_ALLOW_RETRY to avoid any risk
+                        * of starvation.
+                        */
+                       flags &= ~FAULT_FLAG_ALLOW_RETRY;
+                       flags |= FAULT_FLAG_TRIED;
+                       if (!fatal_signal_pending(current))
+                               goto retry;
+               }
+               /* We will enter mm_fault_error() below */
+       }
+
        if (unlikely(fault & (VM_FAULT_RETRY|VM_FAULT_ERROR))) {
                if (fault & VM_FAULT_SIGSEGV)
                        goto bad_area;
@@ -469,38 +489,27 @@ good_area:
        }
 
        /*
-        * Major/minor page fault accounting is only done on the
-        * initial attempt. If we go through a retry, it is extremely
-        * likely that the page will be found in page cache at that point.
+        * Major/minor page fault accounting.
         */
-       if (flags & FAULT_FLAG_ALLOW_RETRY) {
-               if (fault & VM_FAULT_MAJOR) {
-                       current->maj_flt++;
-                       perf_sw_event(PERF_COUNT_SW_PAGE_FAULTS_MAJ, 1,
-                                     regs, address);
+       if (fault & VM_FAULT_MAJOR) {
+               current->maj_flt++;
+               perf_sw_event(PERF_COUNT_SW_PAGE_FAULTS_MAJ, 1,
+                             regs, address);
 #ifdef CONFIG_PPC_SMLPAR
-                       if (firmware_has_feature(FW_FEATURE_CMO)) {
-                               u32 page_ins;
-
-                               preempt_disable();
-                               page_ins = be32_to_cpu(get_lppaca()->page_ins);
-                               page_ins += 1 << PAGE_FACTOR;
-                               get_lppaca()->page_ins = cpu_to_be32(page_ins);
-                               preempt_enable();
-                       }
-#endif /* CONFIG_PPC_SMLPAR */
-               } else {
-                       current->min_flt++;
-                       perf_sw_event(PERF_COUNT_SW_PAGE_FAULTS_MIN, 1,
-                                     regs, address);
-               }
-               if (fault & VM_FAULT_RETRY) {
-                       /* Clear FAULT_FLAG_ALLOW_RETRY to avoid any risk
-                        * of starvation. */
-                       flags &= ~FAULT_FLAG_ALLOW_RETRY;
-                       flags |= FAULT_FLAG_TRIED;
-                       goto retry;
+               if (firmware_has_feature(FW_FEATURE_CMO)) {
+                       u32 page_ins;
+
+                       preempt_disable();
+                       page_ins = be32_to_cpu(get_lppaca()->page_ins);
+                       page_ins += 1 << PAGE_FACTOR;
+                       get_lppaca()->page_ins = cpu_to_be32(page_ins);
+                       preempt_enable();
                }
+#endif /* CONFIG_PPC_SMLPAR */
+       } else {
+               current->min_flt++;
+               perf_sw_event(PERF_COUNT_SW_PAGE_FAULTS_MIN, 1,
+                             regs, address);
        }
 
        up_read(&mm->mmap_sem);