From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-5.3 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,USER_AGENT_MUTT autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id CB92CC48BD6 for ; Tue, 25 Jun 2019 19:08:42 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id A383B208CA for ; Tue, 25 Jun 2019 19:08:42 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1731822AbfFYTIl (ORCPT ); Tue, 25 Jun 2019 15:08:41 -0400 Received: from mx1.redhat.com ([209.132.183.28]:58468 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727684AbfFYTIk (ORCPT ); Tue, 25 Jun 2019 15:08:40 -0400 Received: from smtp.corp.redhat.com (int-mx02.intmail.prod.int.phx2.redhat.com [10.5.11.12]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id 35F8930C1AFD; Tue, 25 Jun 2019 19:08:40 +0000 (UTC) Received: from redhat.com (dhcp-17-153.bos.redhat.com [10.18.17.153]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 8A36E60BE5; Tue, 25 Jun 2019 19:08:38 +0000 (UTC) Date: Tue, 25 Jun 2019 15:08:36 -0400 From: Joe Lawrence To: Miroslav Benes Cc: Petr Mladek , linux-kernel@vger.kernel.org, live-patching@vger.kernel.org, linux-kbuild@vger.kernel.org Subject: Re: [PATCH v4 00/10] klp-convert livepatch build tooling Message-ID: <20190625190836.GL20356@redhat.com> References: <20190509143859.9050-1-joe.lawrence@redhat.com> <20190614083435.uq3mk6mprbatysol@pathway.suse.cz> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.11.4 (2019-03-13) X-Scanned-By: MIMEDefang 2.79 on 10.5.11.12 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.40]); Tue, 25 Jun 2019 19:08:40 +0000 (UTC) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Jun 25, 2019 at 01:36:37PM +0200, Miroslav Benes wrote: > > [ ... snip ... ] > > If I revert commit d59cadc0a8f8 ("[squash] klp-convert: make > convert_rela() list-safe") (from Joe's expanded github tree), the problem > disappears. > > I haven't spotted any problem in the code and I cannot explain a > dependency on GCC version. Any ideas? > I can confirm that test_klp_convert1.ko crashes with RHEL-7 and its older gcc. I added some debugging printf's to klp-convert and see: % ./scripts/livepatch/klp-convert \ ./Symbols.list \ lib/livepatch/test_klp_convert1.klp.o \ lib/livepatch/test_klp_convert1.ko | \ grep saved_command_line convert_rela: oldsec: .rela.text rela @ 0x1279670 rela->sym @ 0x12791f0 (.klp.sym.vmlinux.saved_command_line,0) offset: 0x3 convert_rela: oldsec: .rela.text rela @ 0x1279cd0 rela->sym @ 0x12791f0 (.klp.sym.vmlinux.saved_command_line,0) offset: 0x9a move_rela: rela @ 0x1279670 rela->sym @ 0x12791f0 (.klp.sym.vmlinux.saved_command_line,0) offset: 0x3 main: skipping rela @ 0x1279cd0 rela->sym @ 0x12791f0 (.klp.sym.vmlinux.saved_command_line,0) (!must_convert) I think the problem is: - Relas at different offsets, but for the same symbol may share symbol storage. Note the same rela->sym value above. - Before d59cadc0a8f8 ("[squash] klp-convert: make convert_rela() list-safe"), convert_rela() iterated through the entire section's relas, moving any of the same name. This was determined not to be list safe when moving consecutive relas in the linked list. - After d59cadc0a8f8 ("[squash] klp-convert: make convert_rela() list-safe"), convert_rela() still iterates through the section relas, but only updates r1->sym->klp_rela_sec instead of moving them. move_rela() was added to be called by the for-each-rela loop in main(). - Bug 1: klp_rela_sec probably belongs in struct rela and not struct symbol - Bug 2: the main loop skips over second, third, etc. matching relas anyway as the shared symbol name will have already been converted The following fix might not be elegant, but I can't think of a clever way to handle the original issue d59cadc0a8f8 ("[squash] klp-convert: make convert_rela() list-safe") as well as these resulting regressions. So I broke out the moving of relas to a seperate loop. That is probably worth a comment and at the same time we might be able to drop some of these other "safe" loop traversals for ordinary list_for_each_entry. -- Joe -->8-- -->8-- -->8-- -->8-- -->8-- -->8-- -->8-- -->8-- -->8-- -->8-- diff --git a/scripts/livepatch/elf.h b/scripts/livepatch/elf.h index 7551409..57a8242 100644 --- a/scripts/livepatch/elf.h +++ b/scripts/livepatch/elf.h @@ -33,7 +33,6 @@ struct symbol { struct list_head list; GElf_Sym sym; struct section *sec; - struct section *klp_rela_sec; char *name; unsigned int idx; unsigned char bind, type; @@ -45,6 +44,7 @@ struct rela { struct list_head list; GElf_Rela rela; struct symbol *sym; + struct section *klp_rela_sec; unsigned int type; unsigned long offset; int addend; diff --git a/scripts/livepatch/klp-convert.c b/scripts/livepatch/klp-convert.c index b5873ab..50d6471 100644 --- a/scripts/livepatch/klp-convert.c +++ b/scripts/livepatch/klp-convert.c @@ -525,7 +525,7 @@ static bool convert_rela(struct section *oldsec, struct rela *r, list_for_each_entry_safe(r1, r2, &oldsec->relas, list) { if (r1->sym->name == r->sym->name) { - r1->sym->klp_rela_sec = sec; + r1->klp_rela_sec = sec; } } return true; @@ -535,7 +535,7 @@ static void move_rela(struct rela *r) { /* Move the converted rela to klp rela section */ list_del(&r->list); - list_add(&r->list, &r->sym->klp_rela_sec->relas); + list_add(&r->list, &r->klp_rela_sec->relas); } /* Checks if given symbol name matches a symbol in exp_symbols */ @@ -687,8 +687,11 @@ int main(int argc, const char **argv) return -1; } } + } - move_rela(rela); + list_for_each_entry_safe(rela, tmprela, &sec->relas, list) { + if (is_converted(rela->sym->name)) + move_rela(rela); } }