[PATCH bpf-next 1/9] mm: Bring back mmap_write_trylock()

[Alexei Starovoitov <alexei.starovoitov@gmail.com>]

From: Alexei Starovoitov <ast@kernel.org>

Commit cf95e337cb63 ("mm: delete mmap_write_trylock() and
vma_try_start_write()") removed it when khugepaged stopped using it.
uprobes and dup_mmap() are going to use it.

Signed-off-by: Alexei Starovoitov <ast@kernel.org>
---
 include/linux/mmap_lock.h | 12 ++++++++++++
 1 file changed, 12 insertions(+)

diff --git a/include/linux/mmap_lock.h b/include/linux/mmap_lock.h
index b8a13b8d36a4..e5420b0ce61b 100644
--- a/include/linux/mmap_lock.h
+++ b/include/linux/mmap_lock.h
@@ -566,6 +566,18 @@ static inline int __must_check mmap_write_lock_killable(struct mm_struct *mm)
 	return ret;
 }
 
+static inline bool __must_check mmap_write_trylock(struct mm_struct *mm)
+{
+	bool ret;
+
+	__mmap_lock_trace_start_locking(mm, true);
+	ret = down_write_trylock(&mm->mmap_lock) != 0;
+	if (ret)
+		mm_lock_seqcount_begin(mm);
+	__mmap_lock_trace_acquire_returned(mm, true, ret);
+	return ret;
+}
+
 /*
  * Drop all currently-held per-VMA locks.
  * This is called from the mmap_lock implementation directly before releasing
-- 
2.55.0