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 Received: from lists.gnu.org (lists.gnu.org [209.51.188.17]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id 41E8CC6FD18 for ; Tue, 25 Apr 2023 13:31:26 +0000 (UTC) Received: from localhost ([::1] helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1prIl9-0008Q1-3K; Tue, 25 Apr 2023 09:31:07 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1prIl7-0008Pn-Kj for qemu-devel@nongnu.org; Tue, 25 Apr 2023 09:31:05 -0400 Received: from us-smtp-delivery-124.mimecast.com ([170.10.129.124]) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1prIl5-0001i5-ON for qemu-devel@nongnu.org; Tue, 25 Apr 2023 09:31:05 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1682429463; h=from:from:reply-to:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:mime-version:mime-version: content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=/1HrAEFtifVPb8JOgDveFB1YDo86Gg4kCbxcsscMJ1s=; b=M0ZPhxMr0zSk3PoEV9C0htCy6k/5fzhwGs25PIH7JSRPPN9Nw4TPfXvv8rA0qRKpylF58n F3mPSN7sCs0Rv5uehA53Z8CdVSUtli7kqGnwBRB86/uq57c4yKvLWy2zK01GbXYffOFmF0 ZWM+uMeHEh2DidODPnJUZMkCZcxzcVA= Received: from mimecast-mx02.redhat.com (mimecast-mx02.redhat.com [66.187.233.88]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id us-mta-235-j6NfOabUPHO2XAhOS-0hcw-1; Tue, 25 Apr 2023 09:30:59 -0400 X-MC-Unique: j6NfOabUPHO2XAhOS-0hcw-1 Received: from smtp.corp.redhat.com (int-mx08.intmail.prod.int.rdu2.redhat.com [10.11.54.8]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx02.redhat.com (Postfix) with ESMTPS id 4930B8EE5BA; Tue, 25 Apr 2023 13:30:56 +0000 (UTC) Received: from redhat.com (unknown [10.42.28.55]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 92702C15BA0; Tue, 25 Apr 2023 13:30:52 +0000 (UTC) Date: Tue, 25 Apr 2023 14:30:41 +0100 From: Daniel =?utf-8?B?UC4gQmVycmFuZ8Op?= To: Juan Quintela , =?utf-8?Q?C=C3=A9dric?= Le Goater , qemu-devel@nongnu.org, Peter Maydell , Thomas Huth , Daniel Henrique Barboza , =?utf-8?Q?Marc-Andr=C3=A9?= Lureau , =?utf-8?Q?C=C3=A9dric?= Le Goater , Stefan Hajnoczi , Paolo Bonzini Subject: Re: [PATCH] async: Suppress GCC13 false positive in aio_bh_poll() Message-ID: References: <20230420202939.1982044-1-clg@kaod.org> <87a5ywgkqg.fsf@secure.mitica> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: User-Agent: Mutt/2.2.9 (2022-11-12) X-Scanned-By: MIMEDefang 3.1 on 10.11.54.8 Received-SPF: pass client-ip=170.10.129.124; envelope-from=berrange@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -22 X-Spam_score: -2.3 X-Spam_bar: -- X-Spam_report: (-2.3 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.171, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_NONE=-0.0001, RCVD_IN_MSPIKE_H2=-0.001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001, T_SCC_BODY_TEXT_LINE=-0.01 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Reply-To: Daniel =?utf-8?B?UC4gQmVycmFuZ8Op?= Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org On Tue, Apr 25, 2023 at 02:24:59PM +0100, Daniel P. Berrangé wrote: > On Tue, Apr 25, 2023 at 03:22:15PM +0200, Juan Quintela wrote: > > Cédric Le Goater wrote: > > > From: Cédric Le Goater > > > > > > GCC13 reports an error : > > > > > > ../util/async.c: In function ‘aio_bh_poll’: > > > include/qemu/queue.h:303:22: error: storing the address of local > > > variable ‘slice’ in ‘*ctx.bh_slice_list.sqh_last’ > > > [-Werror=dangling-pointer=] > > > 303 | (head)->sqh_last = &(elm)->field.sqe_next; \ > > > | ~~~~~~~~~~~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~ > > > ../util/async.c:169:5: note: in expansion of macro ‘QSIMPLEQ_INSERT_TAIL’ > > > 169 | QSIMPLEQ_INSERT_TAIL(&ctx->bh_slice_list, &slice, next); > > > | ^~~~~~~~~~~~~~~~~~~~ > > > ../util/async.c:161:17: note: ‘slice’ declared here > > > 161 | BHListSlice slice; > > > | ^~~~~ > > > ../util/async.c:161:17: note: ‘ctx’ declared here > > > > > > But the local variable 'slice' is removed from the global context list > > > in following loop of the same routine. Add a pragma to silent GCC. > > > > > > Cc: Stefan Hajnoczi > > > Cc: Paolo Bonzini > > > Cc: Daniel P. Berrangé > > > Signed-off-by: Cédric Le Goater > > > --- > > > util/async.c | 14 ++++++++++++++ > > > 1 file changed, 14 insertions(+) > > > > > > diff --git a/util/async.c b/util/async.c > > > index 21016a1ac7..856e1a8a33 100644 > > > --- a/util/async.c > > > +++ b/util/async.c > > > @@ -164,7 +164,21 @@ int aio_bh_poll(AioContext *ctx) > > > > > > /* Synchronizes with QSLIST_INSERT_HEAD_ATOMIC in aio_bh_enqueue(). */ > > > QSLIST_MOVE_ATOMIC(&slice.bh_list, &ctx->bh_list); > > > + > > > + /* > > > + * GCC13 [-Werror=dangling-pointer=] complains that the local variable > > > + * 'slice' is being stored in the global 'ctx->bh_slice_list' but the > > > + * list is emptied before this function returns. > > > + */ > > > +#if !defined(__clang__) > > > +#pragma GCC diagnostic push > > > +#pragma GCC diagnostic ignored "-Wpragmas" > > > +#pragma GCC diagnostic ignored "-Wdangling-pointer=" > > > +#endif > > > QSIMPLEQ_INSERT_TAIL(&ctx->bh_slice_list, &slice, next); > > > +#if !defined(__clang__) > > > +#pragma GCC diagnostic pop > > > +#endif > > > > > > while ((s = QSIMPLEQ_FIRST(&ctx->bh_slice_list))) { > > > QEMUBH *bh; > > > > I know, I know. > > > > I like to make fun of the compiler as the next guy. But it is not > > simpler this other change, just put the variable in the heap? > > > > Later, Juan. > > > > > > From bb5792a6763a451c72ef5cfd78b09032689f54e5 Mon Sep 17 00:00:00 2001 > > From: Juan Quintela > > Date: Tue, 25 Apr 2023 15:19:11 +0200 > > Subject: [PATCH] Silent GCC13 warning > > > > Gcc complains about putting a local variable on a global list, not > > noticing that we remove the whole list before leaving the function. > > > > Signed-off-by: Juan Quintela > > --- > > util/async.c | 10 +++++++--- > > 1 file changed, 7 insertions(+), 3 deletions(-) > > > > diff --git a/util/async.c b/util/async.c > > index 21016a1ac7..7a8432e9e9 100644 > > --- a/util/async.c > > +++ b/util/async.c > > @@ -158,13 +158,17 @@ void aio_bh_call(QEMUBH *bh) > > /* Multiple occurrences of aio_bh_poll cannot be called concurrently. */ > > int aio_bh_poll(AioContext *ctx) > > { > > - BHListSlice slice; > > + /* > > + * gcc13 complains about putting a local variable > > + * in a global list, so put it on the heap. > > + */ > > + g_autofree BHListSlice *slice = g_new(BHListSlice, 1); > > BHListSlice *s; > > int ret = 0; > > > > /* Synchronizes with QSLIST_INSERT_HEAD_ATOMIC in aio_bh_enqueue(). */ > > - QSLIST_MOVE_ATOMIC(&slice.bh_list, &ctx->bh_list); > > - QSIMPLEQ_INSERT_TAIL(&ctx->bh_slice_list, &slice, next); > > + QSLIST_MOVE_ATOMIC(&slice->bh_list, &ctx->bh_list); > > + QSIMPLEQ_INSERT_TAIL(&ctx->bh_slice_list, slice, next); > > > > while ((s = QSIMPLEQ_FIRST(&ctx->bh_slice_list))) { > > QEMUBH *bh; > > This must be a memory leak since you're adding a g_new but not > adding any g_free Sorry, I'm failing to read properly today. It uses g_autofree so there is no leak. With regards, Daniel -- |: https://berrange.com -o- https://www.flickr.com/photos/dberrange :| |: https://libvirt.org -o- https://fstop138.berrange.com :| |: https://entangle-photo.org -o- https://www.instagram.com/dberrange :|