On Mon 29-02-16 18:23:34, Oleg Nesterov wrote:

On 02/29, Michal Hocko wrote:

quoted

@@ -267,7 +267,10 @@ static int __bprm_mm_init(struct linux_binprm *bprm)
 	if (!vma)
 		return -ENOMEM;
 
-	down_write(&mm->mmap_sem);
+	if (down_write_killable(&mm->mmap_sem)) {
+		err = -EINTR;
+		goto err_free;
+	}
 	vma->vm_mm = mm;

I won't argue, but this looks unnecessary. Nobody else can see this new mm,
down_write() can't block.

In fact I think we can just remove down_write/up_write here. Except perhaps
there is lockdep_assert_held() somewhere in these paths.

This is what I had initially but then I've noticed that mm_alloc() does
mm_init(current)->init_new_context(current) so the outside can see this
mm AFAICS. Now I guess this shouldn't matter in the real life but the
code doesn't seem much harder to follow, the callers are already
handling all error paths so I guess it would be better to simply move on
this. Or am I misunderstanding the code or missing something?

-- 
Michal Hocko
SUSE Labs

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