[PATCH 07/18] mm, proc: make clear_refs killable

[Michal Hocko]

From: Michal Hocko <mhocko@xxxxxxxx>

CLEAR_REFS_MM_HIWATER_RSS and CLEAR_REFS_SOFT_DIRTY are relying on
mmap_sem for write. If the waiting task gets killed by the oom killer
and it would operate on the current's mm it would block oom_reaper from
asynchronous address space reclaim and reduce the chances of timely OOM
resolving. Wait for the lock in the killable mode and return with EINTR
if the task got killed while waiting. This will also expedite the return
to the userspace and do_exit even if the mm is remote.

Cc: Petr Cermak <petrcermak@xxxxxxxxxxxx>
Acked-by: Oleg Nesterov <oleg@xxxxxxxxxx>
Acked-by: Vlastimil Babka <vbabka@xxxxxxx>
Signed-off-by: Michal Hocko <mhocko@xxxxxxxx>
---
 fs/proc/task_mmu.c | 11 +++++++++--
 1 file changed, 9 insertions(+), 2 deletions(-)

diff --git a/fs/proc/task_mmu.c b/fs/proc/task_mmu.c
index 541583510cfb..4648c7f63ae2 100644
--- a/fs/proc/task_mmu.c
+++ b/fs/proc/task_mmu.c
@@ -1027,11 +1027,15 @@ static ssize_t clear_refs_write(struct file *file, const char __user *buf,
 		};
 
 		if (type == CLEAR_REFS_MM_HIWATER_RSS) {
+			if (down_write_killable(&mm->mmap_sem)) {
+				count = -EINTR;
+				goto out_mm;
+			}
+
 			/*
 			 * Writing 5 to /proc/pid/clear_refs resets the peak
 			 * resident set size to this mm's current rss value.
 			 */
-			down_write(&mm->mmap_sem);
 			reset_mm_hiwater_rss(mm);
 			up_write(&mm->mmap_sem);
 			goto out_mm;
@@ -1043,7 +1047,10 @@ static ssize_t clear_refs_write(struct file *file, const char __user *buf,
 				if (!(vma->vm_flags & VM_SOFTDIRTY))
 					continue;
 				up_read(&mm->mmap_sem);
-				down_write(&mm->mmap_sem);
+				if (down_write_killable(&mm->mmap_sem)) {
+					count = -EINTR;
+					goto out_mm;
+				}
 				for (vma = mm->mmap; vma; vma = vma->vm_next) {
 					vma->vm_flags &= ~VM_SOFTDIRTY;
 					vma_set_page_prot(vma);
-- 
2.8.0.rc3