um/kernel/trap.c: port OOM changes to handle_page_fault()

Commit d065bd810b6d ("mm: retry page fault when blocking on disk
transfer") and commit 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 um.

Signed-off-by: Kautuk Consul <consul.kautuk@gmail.com>
Cc: Jeff Dike <jdike@addtoit.com>
Cc: Richard Weinberger <richard@nod.at>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 19 insertions, 5 deletions

diff --git a/arch/um/kernel/trap.c b/arch/um/kernel/trap.c
index dafc94715950..3be60765c0e2 100644
--- a/arch/um/kernel/trap.c
+++ b/arch/um/kernel/trap.c
@@ -30,6 +30,8 @@ int handle_page_fault(unsigned long address, unsigned long ip,
         pmd_t *pmd;
         pte_t *pte;
         int err = -EFAULT;
+        unsigned int flags = FAULT_FLAG_ALLOW_RETRY | FAULT_FLAG_KILLABLE |
+                                 (is_write ? FAULT_FLAG_WRITE : 0);
 
         *code_out = SEGV_MAPERR;
 
@@ -40,6 +42,7 @@ int handle_page_fault(unsigned long address, unsigned long ip,
         if (in_atomic())
                 goto out_nosemaphore;
 
+retry:
         down_read(&mm->mmap_sem);
         vma = find_vma(mm, address);
         if (!vma)
@@ -65,7 +68,11 @@ good_area:
         do {
                 int 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))
+                        goto out_nosemaphore;
+
                 if (unlikely(fault & VM_FAULT_ERROR)) {
                         if (fault & VM_FAULT_OOM) {
                                 goto out_of_memory;
@@ -75,10 +82,17 @@ good_area:
                         }
                         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;
+
+                                goto retry;
+                        }
+                }
 
                 pgd = pgd_offset(mm, address);
                 pud = pud_offset(pgd, address);