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From:   Wei Yang <richard.weiyang@linux.alibaba.com>
To:     akpm@linux-foundation.org
Cc:     linux-mm@kvack.org, linux-kernel@vger.kernel.org,
        Wei Yang <richard.weiyang@linux.alibaba.com>
Subject: [PATCH] mm/mempolicy: remove or narrow the lock on current
Date:   Mon, 21 Sep 2020 12:04:16 +0800
Message-Id: <20200921040416.86185-1-richard.weiyang@linux.alibaba.com>
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It is not necessary to hold the lock of current when setting nodemask of
a new policy.

Signed-off-by: Wei Yang <richard.weiyang@linux.alibaba.com>
---
 mm/mempolicy.c | 5 +----
 1 file changed, 1 insertion(+), 4 deletions(-)

diff --git a/mm/mempolicy.c b/mm/mempolicy.c
index 906adc58d86f..3fde772ef5ef 100644
--- a/mm/mempolicy.c
+++ b/mm/mempolicy.c
@@ -875,13 +875,12 @@ static long do_set_mempolicy(unsigned short mode, unsigned short flags,
 		goto out;
 	}
 
-	task_lock(current);
 	ret = mpol_set_nodemask(new, nodes, scratch);
 	if (ret) {
-		task_unlock(current);
 		mpol_put(new);
 		goto out;
 	}
+	task_lock(current);
 	old = current->mempolicy;
 	current->mempolicy = new;
 	if (new && new->mode == MPOL_INTERLEAVE)
@@ -1324,9 +1323,7 @@ static long do_mbind(unsigned long start, unsigned long len,
 		NODEMASK_SCRATCH(scratch);
 		if (scratch) {
 			mmap_write_lock(mm);
-			task_lock(current);
 			err = mpol_set_nodemask(new, nmask, scratch);
-			task_unlock(current);
 			if (err)
 				mmap_write_unlock(mm);
 		} else
-- 
2.20.1 (Apple Git-117)