From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-qt1-x829.google.com (mail-qt1-x829.google.com [IPv6:2607:f8b0:4864:20::829]) by sourceware.org (Postfix) with ESMTPS id 6B350394DAD7 for ; Thu, 15 Apr 2021 19:45:53 +0000 (GMT) DMARC-Filter: OpenDMARC Filter v1.3.2 sourceware.org 6B350394DAD7 Received: by mail-qt1-x829.google.com with SMTP id o2so5717531qtr.4 for ; Thu, 15 Apr 2021 12:45:53 -0700 (PDT) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:subject:to:references:from:message-id:date :user-agent:mime-version:in-reply-to:content-language :content-transfer-encoding; bh=R0tyMrnLJ9Nva3uUMLXGVriczxGvdrXNUuyUsKR9xoE=; b=SLe42wF+8TwdhJPKjZha8iWK64rzNPaVHZ/CLV8C3hILFnkCGw1EIclIvLXuirtGlQ /4qRfiFjV0u5BoGsUEFbj34Ml7Tq1376euf1prN7wpqLj370JI5VgtYF1Ns+h1zGBBfg lJSUB9kuZwmEmXDm8Bds+9ZpXfNg728s6A1h+2MmCef5Bgs5LcPYvoHN0536ZCklXcrI 3Rjf7ic69nG2aSLzDBOd0N0YnXJImJIFDuS22pNN2oG8ovlxGF0krMvAo038sgqTHxHB 00M5oXuUAq24YmdfzkUmQBNakQmw2xRWQKiaLjTRhHP3OJkJYpVa7Y24v+b7fjdTaU41 tG/w== X-Gm-Message-State: AOAM5337W3p4LjTmORDLfww+JcKaw/Zh24nCRqEW/qyhTX3NgDpI85Gg S9zr8LUwHy3ZJWvua3B0I5RGoheL3UwVGwGU X-Google-Smtp-Source: ABdhPJxtjH1iwbAP2y7ACgu0CRZB3ZUz3fYgQ/KNHInqG14UmWzjb/YIcrsF2ufS5dS6WTPldjIKoQ== X-Received: by 2002:ac8:44d0:: with SMTP id b16mr4482896qto.217.1618515952968; Thu, 15 Apr 2021 12:45:52 -0700 (PDT) Received: from [192.168.1.132] ([177.194.41.149]) by smtp.gmail.com with ESMTPSA id k13sm1838411qtm.64.2021.04.15.12.45.51 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Thu, 15 Apr 2021 12:45:52 -0700 (PDT) Subject: Re: [PATCH v2 08/14] elf: Fix DTV gap reuse logic [BZ #27135] To: libc-alpha@sourceware.org, Szabolcs Nagy References: <299d28c6695cd2e76f222b0d36b17b7124c549e7.1618301209.git.szabolcs.nagy@arm.com> From: Adhemerval Zanella Message-ID: Date: Thu, 15 Apr 2021 16:45:50 -0300 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.7.1 MIME-Version: 1.0 In-Reply-To: <299d28c6695cd2e76f222b0d36b17b7124c549e7.1618301209.git.szabolcs.nagy@arm.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit X-Spam-Status: No, score=-12.5 required=5.0 tests=BAYES_00, DKIM_SIGNED, DKIM_VALID, DKIM_VALID_AU, DKIM_VALID_EF, GIT_PATCH_0, NICE_REPLY_A, RCVD_IN_DNSWL_NONE, SPF_HELO_NONE, SPF_PASS, TXREP autolearn=ham autolearn_force=no version=3.4.2 X-Spam-Checker-Version: SpamAssassin 3.4.2 (2018-09-13) on server2.sourceware.org X-BeenThere: libc-alpha@sourceware.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Libc-alpha mailing list List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Thu, 15 Apr 2021 19:45:55 -0000 On 13/04/2021 05:20, Szabolcs Nagy via Libc-alpha wrote: > For some reason only dlopen failure caused dtv gaps to be reused. > > It is possible that the intent was to never reuse modids for a > different module, but after dlopen failure all gaps are reused > not just the ones caused by the unfinished dlopened. > > So the code has to handle reused modids already which seems to > work, however the data races at thread creation and tls access > (see bug 19329 and bug 27111) may be more severe if slots are > reused so this is scheduled after those fixes. I think fixing > the races are not simpler if reuse is disallowed and reuse has > other benefits, so set GL(dl_tls_dtv_gaps) whenever entries are > removed from the middle of the slotinfo list. The value does > not have to be correct: incorrect true value causes the next > modid query to do a slotinfo walk, incorrect false will leave > gaps and new entries are added at the end. > > Fixes bug 27135. LGTM, thanks. Reviewed-by: Adhemerval Zanella > --- > elf/dl-close.c | 6 +++++- > elf/dl-open.c | 10 ---------- > elf/dl-tls.c | 5 +---- > 3 files changed, 6 insertions(+), 15 deletions(-) > > diff --git a/elf/dl-close.c b/elf/dl-close.c > index 3720e47dd1..9f31532f41 100644 > --- a/elf/dl-close.c > +++ b/elf/dl-close.c > @@ -88,7 +88,11 @@ remove_slotinfo (size_t idx, struct dtv_slotinfo_list *listp, size_t disp, > /* If this is not the last currently used entry no need to look > further. */ > if (idx != GL(dl_tls_max_dtv_idx)) > - return true; > + { > + /* There is an unused dtv entry in the middle. */ > + GL(dl_tls_dtv_gaps) = true; > + return true; > + } > } > > while (idx - disp > (disp == 0 ? 1 + GL(dl_tls_static_nelem) : 0)) Ok. > diff --git a/elf/dl-open.c b/elf/dl-open.c > index 83b8e96a5c..661f26977e 100644 > --- a/elf/dl-open.c > +++ b/elf/dl-open.c > @@ -890,16 +890,6 @@ no more namespaces available for dlmopen()")); > state if relocation failed, for example. */ > if (args.map) > { > - /* Maybe some of the modules which were loaded use TLS. > - Since it will be removed in the following _dl_close call > - we have to mark the dtv array as having gaps to fill the > - holes. This is a pessimistic assumption which won't hurt > - if not true. There is no need to do this when we are > - loading the auditing DSOs since TLS has not yet been set > - up. */ > - if ((mode & __RTLD_AUDIT) == 0) > - GL(dl_tls_dtv_gaps) = true; > - > _dl_close_worker (args.map, true); > > /* All l_nodelete_pending objects should have been deleted Ok. > diff --git a/elf/dl-tls.c b/elf/dl-tls.c > index c4466bd9fc..b0257185e9 100644 > --- a/elf/dl-tls.c > +++ b/elf/dl-tls.c > @@ -187,10 +187,7 @@ _dl_next_tls_modid (void) > size_t > _dl_count_modids (void) > { > - /* It is rare that we have gaps; see elf/dl-open.c (_dl_open) where > - we fail to load a module and unload it leaving a gap. If we don't > - have gaps then the number of modids is the current maximum so > - return that. */ > + /* The count is the max unless dlclose or failed dlopen created gaps. */ > if (__glibc_likely (!GL(dl_tls_dtv_gaps))) > return GL(dl_tls_max_dtv_idx); > > Ok.