Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753036AbcJKNWH (ORCPT ); Tue, 11 Oct 2016 09:22:07 -0400 Received: from sender153-mail.zoho.com ([74.201.84.153]:25456 "EHLO sender153-mail.zoho.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751518AbcJKNWF (ORCPT ); Tue, 11 Oct 2016 09:22:05 -0400 DomainKey-Signature: a=rsa-sha1; q=dns; c=nofws; s=zapps768; d=zoho.com; h=cc:from:subject:to:message-id:date:user-agent:mime-version:content-type; b=VeZbEh/sFTFjgCA5wwZwUoFSRmE0rXDpjsEYYibmiSUEp7CHVgyw8KLfTAt2NdZJBdiK71ZzGFIw O9Ru1GfhFlfz8IN4iR6pxyCsyBiOoyOKiYeNQWVaPE1qdKJKLAzI Cc: zijun_hu@htc.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org, cl@linux.com From: zijun_hu Subject: [RFC PATCH] mm/percpu.c: fix panic triggered by BUG_ON() falsely To: tj@kernel.org, akpm@linux-foundation.org Message-ID: <7ed31efd-a59a-0a74-1145-c1af3c3d0d73@zoho.com> Date: Tue, 11 Oct 2016 21:03:26 +0800 User-Agent: Mozilla/5.0 (Windows NT 6.1; WOW64; rv:45.0) Gecko/20100101 Thunderbird/45.3.0 MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2387 Lines: 73 From: zijun_hu as shown by pcpu_build_alloc_info(), the number of units within a percpu group is educed by rounding up the number of CPUs within the group to @upa boundary, therefore, the number of CPUs isn't equal to the units's if it isn't aligned to @upa normally. however, pcpu_page_first_chunk() uses BUG_ON() to assert one number is equal the other roughly, so a panic is maybe triggered by the BUG_ON() falsely. in order to fix this issue, the number of CPUs is rounded up then compared with units's, the BUG_ON() is replaced by warning and returning error code as well to keep system alive as much as possible. Signed-off-by: zijun_hu --- mm/percpu.c | 16 ++++++++++++---- 1 file changed, 12 insertions(+), 4 deletions(-) diff --git a/mm/percpu.c b/mm/percpu.c index 32e2d8d128c1..c2f0d9734d8c 100644 --- a/mm/percpu.c +++ b/mm/percpu.c @@ -2095,6 +2095,8 @@ int __init pcpu_page_first_chunk(size_t reserved_size, size_t pages_size; struct page **pages; int unit, i, j, rc; + int upa; + int nr_g0_units; snprintf(psize_str, sizeof(psize_str), "%luK", PAGE_SIZE >> 10); @@ -2102,7 +2104,12 @@ int __init pcpu_page_first_chunk(size_t reserved_size, if (IS_ERR(ai)) return PTR_ERR(ai); BUG_ON(ai->nr_groups != 1); - BUG_ON(ai->groups[0].nr_units != num_possible_cpus()); + upa = ai->alloc_size/ai->unit_size; + g0_nr_units = roundup(num_possible_cpus(), upa); + if (unlikely(WARN_ON(ai->groups[0].nr_units != nr_g0_units))) { + pcpu_free_alloc_info(ai); + return -EINVAL; + } unit_pages = ai->unit_size >> PAGE_SHIFT; @@ -2113,21 +2120,22 @@ int __init pcpu_page_first_chunk(size_t reserved_size, /* allocate pages */ j = 0; - for (unit = 0; unit < num_possible_cpus(); unit++) + for (unit = 0; unit < num_possible_cpus(); unit++) { + unsigned int cpu = ai->groups[0].cpu_map[unit]; for (i = 0; i < unit_pages; i++) { - unsigned int cpu = ai->groups[0].cpu_map[unit]; void *ptr; ptr = alloc_fn(cpu, PAGE_SIZE, PAGE_SIZE); if (!ptr) { pr_warn("failed to allocate %s page for cpu%u\n", - psize_str, cpu); + psize_str, cpu); goto enomem; } /* kmemleak tracks the percpu allocations separately */ kmemleak_free(ptr); pages[j++] = virt_to_page(ptr); } + } /* allocate vm area, map the pages and copy static data */ vm.flags = VM_ALLOC; -- 1.9.1