[PATCH 3/4] mm/madvise: employ mmget_still_valid for write lock

[Minchan Kim <minchan@kernel.org>]

From: Oleksandr Natalenko <oleksandr@redhat.com>

Do the very same trick as we already do since 04f5866e41fb. KSM hints
will require locking mmap_sem for write since they modify vm_flags, so
for remote KSM hinting this additional check is needed.

Signed-off-by: Oleksandr Natalenko <oleksandr@redhat.com>
Signed-off-by: Minchan Kim <minchan@kernel.org>
---
 mm/madvise.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/mm/madvise.c b/mm/madvise.c
index e15dfb4df7bf..eb42b2b7f49b 100644
--- a/mm/madvise.c
+++ b/mm/madvise.c
@@ -1059,6 +1059,8 @@ static int madvise_common(struct task_struct *task, struct mm_struct *mm,
 	if (write) {
 		if (down_write_killable(&mm->mmap_sem))
 			return -EINTR;
+		if (current->mm != mm && !mmget_still_valid(mm))
+			goto skip_mm;
 	} else {
 		down_read(&mm->mmap_sem);
 	}
@@ -1109,6 +1111,7 @@ static int madvise_common(struct task_struct *task, struct mm_struct *mm,
 	}
 out:
 	blk_finish_plug(&plug);
+skip_mm:
 	if (write)
 		up_write(&mm->mmap_sem);
 	else
-- 
2.25.0.rc1.283.g88dfdc4193-goog