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From:   Jia-Ju Bai <baijiaju1990@gmail.com>
To:     akpm@linux-foundation.org, dvyukov@google.com,
        gregkh@linuxfoundation.org, jthumshirn@suse.de,
        pombredanne@nexb.com
Cc:     linux-mm@kvack.org, linux-kernel@vger.kernel.org,
        Jia-Ju Bai <baijiaju1990@gmail.com>
Subject: [PATCH] mm: mempool: Fix a possible sleep-in-atomic-context bug in mempool_resize()
Date:   Thu, 21 Jun 2018 11:07:14 +0800
Message-Id: <20180621030714.10368-1-baijiaju1990@gmail.com>
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

The kernel may sleep with holding a spinlock.
The function call path (from bottom to top) in Linux-4.16.7 is:

[FUNC] remove_element(GFP_KERNEL)
mm/mempool.c, 250: remove_element in mempool_resize
mm/mempool.c, 247: _raw_spin_lock_irqsave in mempool_resize

To fix this bug, GFP_KERNEL is replaced with GFP_ATOMIC.

This bug is found by my static analysis tool (DSAC-2) and checked by
my code review.

Signed-off-by: Jia-Ju Bai <baijiaju1990@gmail.com>
---
 mm/mempool.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/mm/mempool.c b/mm/mempool.c
index 5c9dce34719b..d33bd5d622e7 100644
--- a/mm/mempool.c
+++ b/mm/mempool.c
@@ -247,7 +247,7 @@ int mempool_resize(mempool_t *pool, int new_min_nr)
 	spin_lock_irqsave(&pool->lock, flags);
 	if (new_min_nr <= pool->min_nr) {
 		while (new_min_nr < pool->curr_nr) {
-			element = remove_element(pool, GFP_KERNEL);
+			element = remove_element(pool, GFP_ATOMIC);
 			spin_unlock_irqrestore(&pool->lock, flags);
 			pool->free(element, pool->pool_data);
 			spin_lock_irqsave(&pool->lock, flags);
-- 
2.17.0