From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-qk0-f197.google.com (mail-qk0-f197.google.com [209.85.220.197]) by kanga.kvack.org (Postfix) with ESMTP id 1C2806B0038 for ; Tue, 11 Oct 2016 10:25:49 -0400 (EDT) Received: by mail-qk0-f197.google.com with SMTP id o68so14866499qkf.3 for ; Tue, 11 Oct 2016 07:25:49 -0700 (PDT) Received: from sender153-mail.zoho.com (sender153-mail.zoho.com. [74.201.84.153]) by mx.google.com with ESMTPS id a40si1548827qka.237.2016.10.11.07.25.47 for (version=TLS1 cipher=ECDHE-RSA-AES128-SHA bits=128/128); Tue, 11 Oct 2016 07:25:48 -0700 (PDT) Subject: Re: [RFC PATCH] mm/percpu.c: fix panic triggered by BUG_ON() falsely References: <7ed31efd-a59a-0a74-1145-c1af3c3d0d73@zoho.com> From: zijun_hu Message-ID: Date: Tue, 11 Oct 2016 22:25:31 +0800 MIME-Version: 1.0 In-Reply-To: <7ed31efd-a59a-0a74-1145-c1af3c3d0d73@zoho.com> Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org List-ID: To: tj@kernel.org, akpm@linux-foundation.org Cc: zijun_hu@htc.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org, cl@linux.com Hi all, please ignore this patch since it includes a build error i resend the fixed patch in v2 version i am sorry for my incaution On 2016/10/11 21:03, zijun_hu wrote: > 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; > -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org