mm: make vm_brk killable

Now that all the callers handle vm_brk failure we can change it wait for
mmap_sem killable to help oom_reaper to not get blocked just because
vm_brk gets blocked behind mmap_sem readers.

Signed-off-by: Michal Hocko <mhocko@suse.com>
Acked-by: Vlastimil Babka <vbabka@suse.cz>
Cc: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

include/linux/mm.h

@@ -2011,7 +2011,7 @@ static inline void mm_populate(unsigned long addr, unsigned long len) {}
 #endif
 
 /* These take the mm semaphore themselves */
-extern unsigned long vm_brk(unsigned long, unsigned long);
+extern unsigned long __must_check vm_brk(unsigned long, unsigned long);
 extern int vm_munmap(unsigned long, size_t);
 extern unsigned long __must_check vm_mmap(struct file *, unsigned long,
         unsigned long, unsigned long,

mm/mmap.c

@@ -2712,12 +2712,9 @@ unsigned long vm_brk(unsigned long addr, unsigned long len)
 	unsigned long ret;
 	bool populate;
 
-	/*
-	 * XXX not all users are chcecking the return value, convert
-	 * to down_write_killable after they are able to cope with
-	 * error
-	 */
-	down_write(&mm->mmap_sem);
+	if (down_write_killable(&mm->mmap_sem))
+		return -EINTR;
+
 	ret = do_brk(addr, len);
 	populate = ((mm->def_flags & VM_LOCKED) != 0);
 	up_write(&mm->mmap_sem);