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, 12 insertions, 8 deletions

diff --git a/arch/um/kernel/trap.c b/arch/um/kernel/trap.c
index b2f5adf838dd..5c3aef74237f 100644
--- a/arch/um/kernel/trap.c
+++ b/arch/um/kernel/trap.c
@@ -30,8 +30,7 @@ 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);
+        unsigned int flags = FAULT_FLAG_ALLOW_RETRY | FAULT_FLAG_KILLABLE;
 
         *code_out = SEGV_MAPERR;
 
@@ -42,6 +41,8 @@ int handle_page_fault(unsigned long address, unsigned long ip,
         if (in_atomic())
                 goto out_nosemaphore;
 
+        if (is_user)
+                flags |= FAULT_FLAG_USER;
 retry:
         down_read(&mm->mmap_sem);
         vma = find_vma(mm, address);
@@ -58,12 +59,15 @@ retry:
 
 good_area:
         *code_out = SEGV_ACCERR;
-        if (is_write && !(vma->vm_flags & VM_WRITE))
-                goto out;
-
-        /* Don't require VM_READ|VM_EXEC for write faults! */
-        if (!is_write && !(vma->vm_flags & (VM_READ | VM_EXEC)))
-                goto out;
+        if (is_write) {
+                if (!(vma->vm_flags & VM_WRITE))
+                        goto out;
+                flags |= FAULT_FLAG_WRITE;
+        } else {
+                /* Don't require VM_READ|VM_EXEC for write faults! */
+                if (!(vma->vm_flags & (VM_READ | VM_EXEC)))
+                        goto out;
+        }
 
         do {
                 int fault;