From mboxrd@z Thu Jan 1 00:00:00 1970 Return-path: Received: from mx1.redhat.com ([209.132.183.28]) by bombadil.infradead.org with esmtps (Exim 4.80.1 #2 (Red Hat Linux)) id 1ZPLVa-0000Kz-UY for kexec@lists.infradead.org; Wed, 12 Aug 2015 02:11:15 +0000 From: Baoquan He Subject: [Patch v3] align crash_notes allocation to make it be inside one physical page Date: Wed, 12 Aug 2015 10:10:40 +0800 Message-Id: <1439345440-6752-1-git-send-email-bhe@redhat.com> List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "kexec" Errors-To: kexec-bounces+dwmw2=infradead.org@lists.infradead.org To: akpm@linux-foundation.org, ebiederm@xmission.com, vgoyal@redhat.com, dyoung@redhat.com, mhuang@redhat.com, lisa.mitchell@hp.com, tatsu@ab.jp.nec.com, seiji.aguchi.tr@hitachi.com Cc: kexec@lists.infradead.org, linux-kernel@vger.kernel.org, Baoquan He People reported that crash_notes in /proc/vmcore were corrupted and this cause crash kdump failure. With code debugging and log we got the root cause. This is because percpu variable crash_notes are allocated in 2 vmalloc pages. Currently percpu is based on vmalloc by default. Vmalloc can't guarantee 2 continuous vmalloc pages are also on 2 continuous physical pages. So when 1st kernel exports the starting address and size of crash_notes through sysfs like below: /sys/devices/system/cpu/cpux/crash_notes /sys/devices/system/cpu/cpux/crash_notes_size kdump kernel use them to get the content of crash_notes. However the 2nd part may not be in the next neighbouring physical page as we expected if crash_notes are allocated accross 2 vmalloc pages. That's why nhdr_ptr->n_namesz or nhdr_ptr->n_descsz could be very huge in update_note_header_size_elf64() and cause note header merging failure or some warnings. In this patch change to call __alloc_percpu() to passed in the align value by rounding crash_notes_size up to the nearest power of two. This makes sure the crash_notes is allocated inside one physical page since sizeof(note_buf_t) in all ARCHS is smaller than PAGE_SIZE. Meanwhile add a BUILD_BUG_ON to break compile if size is bigger than PAGE_SIZE since crash_notes definitely will be in 2 pages. That need be avoided, and need be reported if it's unavoidable. v1->v2: Minfei mentioned percpu can't take align value bigger then PAGE_SIZE. So limit align to be PAGE_SIZE at most. v2->v3: Change code and add code comments as Andrew suggested. Signed-off-by: Baoquan He --- kernel/kexec.c | 19 ++++++++++++++++++- 1 file changed, 18 insertions(+), 1 deletion(-) diff --git a/kernel/kexec.c b/kernel/kexec.c index 35d9e0a..293fe64 100644 --- a/kernel/kexec.c +++ b/kernel/kexec.c @@ -1620,7 +1620,24 @@ void crash_save_cpu(struct pt_regs *regs, int cpu) static int __init crash_notes_memory_init(void) { /* Allocate memory for saving cpu registers. */ - crash_notes = alloc_percpu(note_buf_t); + size_t size, align; + + /* crash_notes could be allocated across 2 vmalloc pages when percpu + * is vmalloc based . vmalloc doesn't guarantee 2 continuous vmalloc + * pages are also on 2 continuous physical pages. In this case the + * 2nd part of crash_notes in 2nd page could be lost since only the + * starting address and size of crash_notes are exported through sysfs. + * Here round up the size of crash_notes to the nearest power of two + * and pass it to __alloc_percpu as align value. This can make sure + * crash_notes is allocated inside one physical page. */ + size = sizeof(note_buf_t); + align = min(roundup_pow_of_two(sizeof(note_buf_t)), PAGE_SIZE); + + /* Break compile if size is bigger than PAGE_SIZE since crash_notes + * definitely will be in 2 pages with that. */ + BUILD_BUG_ON(size > PAGE_SIZE); + + crash_notes = __alloc_percpu(size, align); if (!crash_notes) { pr_warn("Kexec: Memory allocation for saving cpu register states failed\n"); return -ENOMEM; -- 1.9.3 _______________________________________________ kexec mailing list kexec@lists.infradead.org http://lists.infradead.org/mailman/listinfo/kexec