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[209.85.220.65]) by mx.google.com with SMTPS id c128sor30940818jac.2.2019.07.01.18.17.06 for (Google Transport Security); Mon, 01 Jul 2019 18:17:06 -0700 (PDT) Received-SPF: pass (google.com: domain of henryburns@google.com designates 209.85.220.65 as permitted sender) client-ip=209.85.220.65; Authentication-Results: mx.google.com; dkim=pass header.i=@google.com header.s=20161025 header.b=E+IhI3EF; spf=pass (google.com: domain of henryburns@google.com designates 209.85.220.65 as permitted sender) smtp.mailfrom=henryburns@google.com; dmarc=pass (p=REJECT sp=REJECT dis=NONE) header.from=google.com DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20161025; h=mime-version:references:in-reply-to:from:date:message-id:subject:to :cc; bh=bGcgCNZM2Fneaix4f2ZBOZNpZLRiuOjV16Tk5yHyGgI=; b=E+IhI3EFrprAxwYz5XL+dCV+y22CzQKMuhlzlsky6+02t5cScdlAo3mb1JWWpTE8JK qOiH8sX9JUtanurv+qeY6OyoQdYIumvOrbXWbMONgeUsy3svK67NSEEVHLTUEnq3T93Z WjZDPGzT/Sm2ne1EOi9XJQs5bBTlLyY4StGuUgRBRl43AIlvqC//mFi9EXC7VsIo0Kh3 jrQZCZJrfABLTciTv3tMxTQGTBUVHUWqVv938g1y0Q16KV5JwOslf+zytRH6fcmtncNz r6/n3C1dVWSPxwTP7ZDAaOUFkZcs4oCQFhYFOT3zAF2OLakwlo+vH3fKStApBz3cwpI7 acHg== X-Google-Smtp-Source: APXvYqy7+tj0nUROT403yhSxQDTNTeUEt7vFZMtJl4pXCrWO7ZosVUwEvdbmELi2qgFA1B4FJn4qM+P2QDcjSMHtJI4= X-Received: by 2002:a05:6638:3d6:: with SMTP id r22mr31783750jaq.71.1562030226625; Mon, 01 Jul 2019 18:17:06 -0700 (PDT) MIME-Version: 1.0 References: <20190702005122.41036-1-henryburns@google.com> In-Reply-To: From: Henry Burns Date: Mon, 1 Jul 2019 18:16:30 -0700 Message-ID: Subject: Re: [PATCH v2] mm/z3fold.c: Lock z3fold page before __SetPageMovable() To: Shakeel Butt Cc: Vitaly Wool , Andrew Morton , Vitaly Vul , Mike Rapoport , Xidong Wang , Jonathan Adams , Linux MM , LKML Content-Type: text/plain; charset="UTF-8" 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 Mon, Jul 1, 2019 at 6:00 PM Shakeel Butt wrote: > > On Mon, Jul 1, 2019 at 5:51 PM Henry Burns wrote: > > > > __SetPageMovable() expects it's page to be locked, but z3fold.c doesn't > > lock the page. Following zsmalloc.c's example we call trylock_page() and > > unlock_page(). Also makes z3fold_page_migrate() assert that newpage is > > passed in locked, as documentation. > > > > Signed-off-by: Henry Burns > > Suggested-by: Vitaly Wool > > --- > > Changelog since v1: > > - Added an if statement around WARN_ON(trylock_page(page)) to avoid > > unlocking a page locked by a someone else. > > > > mm/z3fold.c | 6 +++++- > > 1 file changed, 5 insertions(+), 1 deletion(-) > > > > diff --git a/mm/z3fold.c b/mm/z3fold.c > > index e174d1549734..6341435b9610 100644 > > --- a/mm/z3fold.c > > +++ b/mm/z3fold.c > > @@ -918,7 +918,10 @@ static int z3fold_alloc(struct z3fold_pool *pool, size_t size, gfp_t gfp, > > set_bit(PAGE_HEADLESS, &page->private); > > goto headless; > > } > > - __SetPageMovable(page, pool->inode->i_mapping); > > + if (!WARN_ON(!trylock_page(page))) { > > + __SetPageMovable(page, pool->inode->i_mapping); > > + unlock_page(page); > > + } > > Can you please comment why lock_page() is not used here? Since z3fold_alloc can be called in atomic or non atomic context, calling lock_page() could trigger a number of warnings about might_sleep() being called in atomic context. WARN_ON should avoid the problem described above as well, and in any weird condition where someone else has the page lock, we can avoid calling __SetPageMovable(). > > > z3fold_page_lock(zhdr); > > > > found: > > @@ -1325,6 +1328,7 @@ static int z3fold_page_migrate(struct address_space *mapping, struct page *newpa > > > > VM_BUG_ON_PAGE(!PageMovable(page), page); > > VM_BUG_ON_PAGE(!PageIsolated(page), page); > > + VM_BUG_ON_PAGE(!PageLocked(newpage), newpage); > > > > zhdr = page_address(page); > > pool = zhdr_to_pool(zhdr); > > -- > > 2.22.0.410.gd8fdbe21b5-goog > >