On Mon 29-02-16 18:38:45, Oleg Nesterov wrote:

On 02/29, Michal Hocko wrote:

quoted

--- 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)) {
+				put_task_struct(task);
+				return -EINTR;
+			}
+
 			/*
 			 * 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)) {
+					put_task_struct(task);
+					return -EINTR;
+				}

Both lack mmput() afaics. Don't you need "goto out_mm" rather then "return" ?

Of course I need! Thanks for catching that.

In this case you do not need put_task_struct().

Why not? Both are after get_proc_task which takes a reference to the
task...

I will send an updated patch. Thanks!

-- 
Michal Hocko
SUSE Labs