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 kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by smtp.lore.kernel.org (Postfix) with ESMTP id BC340C636CC for ; Wed, 1 Feb 2023 03:29:26 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id 0C8146B0074; Tue, 31 Jan 2023 22:29:26 -0500 (EST) Received: by kanga.kvack.org (Postfix, from userid 40) id 052D86B0075; Tue, 31 Jan 2023 22:29:25 -0500 (EST) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id E33AF6B0078; Tue, 31 Jan 2023 22:29:25 -0500 (EST) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0010.hostedemail.com [216.40.44.10]) by kanga.kvack.org (Postfix) with ESMTP id D10DF6B0074 for ; Tue, 31 Jan 2023 22:29:25 -0500 (EST) Received: from smtpin18.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay02.hostedemail.com (Postfix) with ESMTP id 9F0BC120611 for ; Wed, 1 Feb 2023 03:29:25 +0000 (UTC) X-FDA: 80417292690.18.036C9F4 Received: from mail-pj1-f52.google.com (mail-pj1-f52.google.com [209.85.216.52]) by imf05.hostedemail.com (Postfix) with ESMTP id C31C110000D for ; Wed, 1 Feb 2023 03:29:23 +0000 (UTC) Authentication-Results: imf05.hostedemail.com; dkim=pass header.d=chromium.org header.s=google header.b="C+/vfvAZ"; spf=pass (imf05.hostedemail.com: domain of senozhatsky@chromium.org designates 209.85.216.52 as permitted sender) smtp.mailfrom=senozhatsky@chromium.org; dmarc=pass (policy=none) header.from=chromium.org ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1675222163; h=from:from:sender:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-type:content-transfer-encoding: in-reply-to:in-reply-to:references:references:dkim-signature; bh=JmQeZUBoUZX187HUvjWB4P6UVqNd4TUY8OlUmfszjwc=; b=SMBXiFUlNhcYFvhSNXKHZ/oi46CrmVsVUrOjeM2WIfEEV6kXW5Yk9qZPw5BXxNakAIZUYf 9awYNMg6eLluY4wADXHEIzLH2ZLXHl4w4wjnaklTArCVjmaoQjg/xArJKU7lk4Uw0Qn1Ee xUZLqaLc1xlJR4ZIc/ERP3zCQycojpk= ARC-Authentication-Results: i=1; imf05.hostedemail.com; dkim=pass header.d=chromium.org header.s=google header.b="C+/vfvAZ"; spf=pass (imf05.hostedemail.com: domain of senozhatsky@chromium.org designates 209.85.216.52 as permitted sender) smtp.mailfrom=senozhatsky@chromium.org; dmarc=pass (policy=none) header.from=chromium.org ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1675222163; a=rsa-sha256; cv=none; b=t1hEVms5l6vePV1gmlYPmAJbs3+njgXmKwfPDDVGYGvlNZtqLvqAjPAEC3VHnXXhvZDW45 rdjbZxj1QU701SGXGb5xlzds8TK8oMuLd/5V8CGIPfkRlwk5v0+wwSHhWgFjemunK6O5vi QGfUspS6QkBrlwLS9XBnqe/YaHwsZcA= Received: by mail-pj1-f52.google.com with SMTP id o13so16065745pjg.2 for ; Tue, 31 Jan 2023 19:29:23 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=chromium.org; s=google; h=in-reply-to:content-disposition:mime-version:references:message-id :subject:cc:to:from:date:from:to:cc:subject:date:message-id:reply-to; bh=JmQeZUBoUZX187HUvjWB4P6UVqNd4TUY8OlUmfszjwc=; b=C+/vfvAZe3T0QD4/Auf4b3emxIXToLiwD+krbxlLJ6pc3648rd/EHau9U23OQVy3Uz H3FDo23DJgzarhcEsQYrQoY11tCyIYRXiX2Y3ZIS61IsZwe3v3EIONXuuj1wgq3UKuax yEOSKQJxjRi0RqnHT1XA3n+TXBXbdT5mqg1JQ= X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=in-reply-to:content-disposition:mime-version:references:message-id :subject:cc:to:from:date:x-gm-message-state:from:to:cc:subject:date :message-id:reply-to; bh=JmQeZUBoUZX187HUvjWB4P6UVqNd4TUY8OlUmfszjwc=; b=MV1o/Z855ShOcDfK098ur9Gl/0DtLxU04NwxsL00kROAEEnqdq3GFE+cuWr+DS/99A nw3+bh21XCm3PkE3nDmA8fkG3MuQEzGhp/c72FdRXipcSp049gJZiFdhXjTOFjRPRvQB IGbsOTaynS56CMDK8U0nfyVX1q2grnsdlE4tKhhZ+OSlxVX8JsyOgO+k8Gc/FfqXTm7M Io0jFhHGovK8117xHwk2AqZEeQdzOgtMYM6/ojjuB+Uh5DnxbQHC3i9ZDrJb646/BgST fkRG8F5m+dfTR6FgISpHKIXc8i6Adqjj5ErhCYpUDtPJdzd5E3koRMkknG2LIe91PdPS f+eA== X-Gm-Message-State: AO0yUKVtD1Ns7iRmGXgdVnpnqGUnD3E9ZnoVi6eFPiAlkwHr79IDUd+s DS3ffEek8JnHfuUd35mKSkIoAw== X-Google-Smtp-Source: AK7set9Ptx0OBM9znPq+YxMiAFHJ6xv76F2CTVkEIVYgI4mPR0y/gu7skJmJbwpZV7suEHrjPsuZJQ== X-Received: by 2002:a17:90b:1b50:b0:22b:e590:68d0 with SMTP id nv16-20020a17090b1b5000b0022be59068d0mr429228pjb.49.1675222162568; Tue, 31 Jan 2023 19:29:22 -0800 (PST) Received: from google.com (KD124209188001.ppp-bb.dion.ne.jp. [124.209.188.1]) by smtp.gmail.com with ESMTPSA id q8-20020a17090a7a8800b0022c01052e92sm175027pjf.56.2023.01.31.19.29.19 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 31 Jan 2023 19:29:22 -0800 (PST) Date: Wed, 1 Feb 2023 12:29:16 +0900 From: Sergey Senozhatsky To: Nhat Pham Cc: Sergey Senozhatsky , akpm@linux-foundation.org, hannes@cmpxchg.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, minchan@kernel.org, ngupta@vflare.org, sjenning@redhat.com, ddstreet@ieee.org, vitaly.wool@konsulko.com, kernel-team@meta.com Subject: Re: [PATCH] zsmalloc: fix a race with deferred_handles storing Message-ID: References: <20230110231701.326724-1-nphamcs@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Rspamd-Server: rspam05 X-Rspamd-Queue-Id: C31C110000D X-Stat-Signature: 6qzhoxkzm6zkpsuwkgodhmunbgotcd67 X-Rspam-User: X-HE-Tag: 1675222163-951612 X-HE-Meta: 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 byrVHMlM EnkH14HA4sY7djsZeh0hQEjhG6VuxFQ5UpqSrLzMopV3CcZxjFF8cIrUO+Q4ULZeEFeVS+iGkURPe3BYiGIKXC2dohSvpmjm14bi1H8tzBmF8aN9+ifdkhdOEcC1Jr9jCWapuhSJ3k+CjPFFkd82dR2psD5sxA3eDYIV61OPth+J/9PkzPKqxzpHMvACBm/6qrXe9K2sIDgczePdnN4LUN+zlvTeGyC7BgA4EH6hfcrObMh/iHb89bibFQEY151C0+sO3PKIxapl4GhzcATJzE2V+B5jmqh0pnyynv1W76SKsdZm1ng+eLAJ+1M0b1EcJEItJFIFBv7UkciVapx8FHqPTuuIj9nMActyU0W6NqY4QwKy+Cv0e4NZ3qeAj82SiWMFO X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On (23/01/31 18:28), Nhat Pham wrote: > > On (23/01/10 15:17), Nhat Pham wrote: > > [..] > > > #ifdef CONFIG_ZPOOL > > > +static void restore_freelist(struct zs_pool *pool, struct size_class *class, > > > + struct zspage *zspage) > > > +{ > > > + unsigned int obj_idx = 0; > > > + unsigned long handle, off = 0; /* off is within-page offset */ > > > + struct page *page = get_first_page(zspage); > > > + struct link_free *prev_free = NULL; > > > + void *prev_page_vaddr = NULL; > > > + > > > + /* in case no free object found */ > > > + set_freeobj(zspage, (unsigned int)(-1UL)); > > > > I'm not following this. I see how -1UL works for link_free, but this > > cast of -1UL to 4 bytes looks suspicious. > > (resending this since I forgot to forward this to other recipients) > > It is a bit convoluted indeed. But the idea is that for the last object, > the last link is given by: > > link->next = -1UL << OBJ_TAG_BITS > > And at malloc time, we update freeobj as follows > set_freeobj(zspage, link->next >> OBJ_TAG_BITS); > > Which means the freeobj value would be set to something like this: > (-1UL << OBJ_TAG_BITS) >> OBJ_TAG_BITS Oh, good point. I see what you did there. > I want to emulate this here (i.e in the case we have no free object). Makes sense. > As for the casting, I believe set_freeobj requires an unsigned int for > the second field. > > Alternatively, to be 100% safe, we can do something like this: > (unsigned int)((-1UL << OBJ_TAG_BITS) >> OBJ_TAG_BITS) > > But I think I got the same result as just (unsigned int)(-1UL) Yeah, I guess they should be the same, as we take the lower 4 bytes only.