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Date:   Fri, 14 Feb 2020 09:05:19 -0800
From:   Minchan Kim <minchan@...nel.org>
To:     Andrew Morton <akpm@...ux-foundation.org>
Cc:     LKML <linux-kernel@...r.kernel.org>, linux-mm <linux-mm@...ck.org>,
        linux-api@...r.kernel.org, oleksandr@...hat.com,
        Suren Baghdasaryan <surenb@...gle.com>,
        Tim Murray <timmurray@...gle.com>,
        Daniel Colascione <dancol@...gle.com>,
        Sandeep Patil <sspatil@...gle.com>,
        Sonny Rao <sonnyrao@...gle.com>,
        Brian Geffon <bgeffon@...gle.com>,
        Michal Hocko <mhocko@...e.com>,
        Johannes Weiner <hannes@...xchg.org>,
        Shakeel Butt <shakeelb@...gle.com>,
        John Dias <joaodias@...gle.com>,
        Joel Fernandes <joel@...lfernandes.org>, sj38.park@...il.com,
        alexander.h.duyck@...ux.intel.com, Jann Horn <jannh@...gle.com>,
        Minchan Kim <minchan@...nel.org>
Subject: [PATCH v5 6/7] mm/madvise: employ mmget_still_valid for write lock

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

diff --git a/mm/madvise.c b/mm/madvise.c
index bbbfea93396a..762a68205e65 100644
--- a/mm/madvise.c
+++ b/mm/madvise.c
@@ -1117,6 +1117,8 @@ int do_madvise(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);
 	}
@@ -1167,6 +1169,7 @@ int do_madvise(struct task_struct *task, struct mm_struct *mm,
 	}
 out:
 	blk_finish_plug(&plug);
+skip_mm:
 	if (write)
 		up_write(&mm->mmap_sem);
 	else
-- 
2.25.0.265.gbab2e86ba0-goog

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