arch: mm: pass userspace fault flag to generic fault handler

Unlike global OOM handling, memory cgroup code will invoke the OOM killer
in any OOM situation because it has no way of telling faults occuring in
kernel context - which could be handled more gracefully - from
user-triggered faults.

Pass a flag that identifies faults originating in user space from the
architecture-specific fault handlers to generic code so that memcg OOM
handling can be improved.

Signed-off-by: Johannes Weiner <hannes@cmpxchg.org>
Reviewed-by: Michal Hocko <mhocko@suse.cz>
Cc: David Rientjes <rientjes@google.com>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: azurIt <azurit@pobox.sk>
Cc: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 4 insertions, 3 deletions

diff --git a/arch/alpha/mm/fault.c b/arch/alpha/mm/fault.c
index 0c4132dd3507..98838a05ba6d 100644
--- a/arch/alpha/mm/fault.c
+++ b/arch/alpha/mm/fault.c
@@ -89,8 +89,7 @@ do_page_fault(unsigned long address, unsigned long mmcsr,
         const struct exception_table_entry *fixup;
         int fault, si_code = SEGV_MAPERR;
         siginfo_t info;
-        unsigned int flags = (FAULT_FLAG_ALLOW_RETRY | FAULT_FLAG_KILLABLE |
-                              (cause > 0 ? FAULT_FLAG_WRITE : 0));
+        unsigned int flags = FAULT_FLAG_ALLOW_RETRY | FAULT_FLAG_KILLABLE;
 
         /* As of EV6, a load into $31/$f31 is a prefetch, and never faults
            (or is suppressed by the PALcode).  Support that for older CPUs
@@ -115,7 +114,8 @@ do_page_fault(unsigned long address, unsigned long mmcsr,
         if (address >= TASK_SIZE)
                 goto vmalloc_fault;
 #endif
-
+        if (user_mode(regs))
+                flags |= FAULT_FLAG_USER;
 retry:
         down_read(&mm->mmap_sem);
         vma = find_vma(mm, address);
@@ -142,6 +142,7 @@ retry:
         } else {
                 if (!(vma->vm_flags & VM_WRITE))
                         goto bad_area;
+                flags |= FAULT_FLAG_WRITE;
         }
 
         /* If for any reason at all we couldn't handle the fault,