Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752111AbdI0Vf2 (ORCPT ); Wed, 27 Sep 2017 17:35:28 -0400 Received: from mail-it0-f65.google.com ([209.85.214.65]:48498 "EHLO mail-it0-f65.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752039AbdI0VfO (ORCPT ); Wed, 27 Sep 2017 17:35:14 -0400 X-Google-Smtp-Source: AOwi7QCjfgJjq5Nt7l8Af0u9wSe1Uf/h1RZ/O3LbyExnHX418XQk+FKxxbbIdgKxKsxuuDdqGIXZGA== From: Dennis Zhou To: Tejun Heo , Christoph Lameter , Luis Henriques Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, Dennis Zhou Subject: [PATCH 2/2] percpu: fix iteration to prevent skipping over block Date: Wed, 27 Sep 2017 16:35:00 -0500 Message-Id: <1506548100-31247-3-git-send-email-dennisszhou@gmail.com> X-Mailer: git-send-email 1.8.5.2 (Apple Git-48) In-Reply-To: <1506548100-31247-1-git-send-email-dennisszhou@gmail.com> References: <1506548100-31247-1-git-send-email-dennisszhou@gmail.com> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1670 Lines: 44 The iterator functions pcpu_next_md_free_region and pcpu_next_fit_region use the block offset to determine if they have checked the area in the prior iteration. However, this causes an issue when the block offset is greater than subsequent block contig hints. If within the iterator it moves to check subsequent blocks, it may fail in the second predicate due to the block offset not being cleared. Thus, this causes the allocator to skip over blocks leading to false failures when allocating from the reserved chunk. While this happens in the general case as well, it will only fail if it cannot allocate a new chunk. This patch resets the block offset to 0 to pass the second predicate when checking subseqent blocks within the iterator function. Signed-off-by: Dennis Zhou Reported-by: Luis Henriques --- mm/percpu.c | 4 ++++ 1 file changed, 4 insertions(+) diff --git a/mm/percpu.c b/mm/percpu.c index 59d44d6..aa121ce 100644 --- a/mm/percpu.c +++ b/mm/percpu.c @@ -353,6 +353,8 @@ static void pcpu_next_md_free_region(struct pcpu_chunk *chunk, int *bit_off, block->contig_hint_start); return; } + /* reset to satisfy the second predicate above */ + block_off = 0; *bits = block->right_free; *bit_off = (i + 1) * PCPU_BITMAP_BLOCK_BITS - block->right_free; @@ -407,6 +409,8 @@ static void pcpu_next_fit_region(struct pcpu_chunk *chunk, int alloc_bits, *bit_off = pcpu_block_off_to_off(i, block->first_free); return; } + /* reset to satisfy the second predicate above */ + block_off = 0; *bit_off = ALIGN(PCPU_BITMAP_BLOCK_BITS - block->right_free, align); -- 1.8.3.1