[PATCH v7 6/7] 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.

Reviewed-by: Suren Baghdasaryan <surenb@google.com>
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 e794367f681e..e77c6c1fad34 100644
--- a/mm/madvise.c
+++ b/mm/madvise.c
@@ -1118,6 +1118,8 @@ int do_madvise(struct task_struct *target_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);
 	}
@@ -1169,6 +1171,7 @@ int do_madvise(struct task_struct *target_task, struct mm_struct *mm,
 	}
 out:
 	blk_finish_plug(&plug);
+skip_mm:
 	if (write)
 		up_write(&mm->mmap_sem);
 	else
-- 
2.25.0.265.gbab2e86ba0-goog