linux-kernel - [PATCH 02/12] percpu: do not search past bitmap when allocating an area

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Message-Id: <20190228021839.55779-3-dennis@kernel.org>
Date:   Wed, 27 Feb 2019 21:18:29 -0500
From:   Dennis Zhou <dennis@...nel.org>
To:     Dennis Zhou <dennis@...nel.org>, Tejun Heo <tj@...nel.org>,
        Christoph Lameter <cl@...ux.com>
Cc:     Vlad Buslov <vladbu@...lanox.com>, kernel-team@...com,
        linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: [PATCH 02/12] percpu: do not search past bitmap when allocating an area

pcpu_find_block_fit() guarantees that a fit is found within
PCPU_BITMAP_BLOCK_BITS. Iteration is used to determine the first fit as
it compares against the block's contig_hint. This can lead to
incorrectly scanning past the end of the bitmap. The behavior was okay
given the check after for bit_off >= end and the correctness of the
hints from pcpu_find_block_fit().

This patch fixes this by bounding the end offset by the number of bits
in a chunk.

Signed-off-by: Dennis Zhou <dennis@...nel.org>
---
 mm/percpu.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/mm/percpu.c b/mm/percpu.c
index 53bd79a617b1..69ca51d238b5 100644
--- a/mm/percpu.c
+++ b/mm/percpu.c
@@ -988,7 +988,8 @@ static int pcpu_alloc_area(struct pcpu_chunk *chunk, int alloc_bits,
 	/*
 	 * Search to find a fit.
 	 */
-	end = start + alloc_bits + PCPU_BITMAP_BLOCK_BITS;
+	end = min_t(int, start + alloc_bits + PCPU_BITMAP_BLOCK_BITS,
+		    pcpu_chunk_map_bits(chunk));
 	bit_off = bitmap_find_next_zero_area(chunk->alloc_map, end, start,
 					     alloc_bits, align_mask);
 	if (bit_off >= end)
-- 
2.17.1