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s=casper.20170209; h=In-Reply-To:Content-Type:MIME-Version: References:Message-ID:Subject:Cc:To:From:Date:Sender:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description; bh=+cewsqIjy3KyilGPYnpep4bhBTgpsrNatr9SSgJPp+A=; b=Xq6rS14iEtk33sZT1twqc2gQB0 jTafc881dELFdZxc453Afl84KSiCv9BlDNWFMmnJqrJ7+pawRB2ciuCtRFt6kKI+67dnyH1Vd/aA7 7recD+wKVjyEya+hf36HVxPE0dSKP9CBNHdVCkNzZWKcJpH/ZJ2zX25TtfW/6NVV1IjRtxvZ+Y3Kf /g0OXDI4v3N1ArJHE3LwyaVlOjJjpbQQ8+YtWS2daRZRHbFa6TRRt+0A3Y+zpZh/i8glAZMVgyLPP PhwAcASqyaMDlSOzGFxhq/JZ5fYkxv2Mq+XkfA5VgxX/Xx+g4UBo2NUNNibb8nZFuAboaixfLddhj uGQILrJg==; Received: from willy by casper.infradead.org with local (Exim 4.94 #2 (Red Hat Linux)) id 1lUVzl-00GNO2-Ap; Thu, 08 Apr 2021 14:51:03 +0000 Date: Thu, 8 Apr 2021 15:50:57 +0100 From: Matthew Wilcox To: David Howells Cc: linux-fsdevel@vger.kernel.org, Linus Torvalds , Alexander Viro , Christoph Hellwig , linux-mm@kvack.org, linux-cachefs@redhat.com, linux-afs@lists.infradead.org, linux-nfs@vger.kernel.org, linux-cifs@vger.kernel.org, ceph-devel@vger.kernel.org, v9fs-developer@lists.sourceforge.net, Trond Myklebust , Anna Schumaker , Steve French , Dominique Martinet , Jeff Layton , David Wysochanski , linux-kernel@vger.kernel.org Subject: Re: [PATCH v6 02/30] mm: Add set/end/wait functions for PG_private_2 Message-ID: <20210408145057.GN2531743@casper.infradead.org> References: <161789062190.6155.12711584466338493050.stgit@warthog.procyon.org.uk> <161789066013.6155.9816857201817288382.stgit@warthog.procyon.org.uk> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <161789066013.6155.9816857201817288382.stgit@warthog.procyon.org.uk> X-Rspamd-Server: rspam03 X-Rspamd-Queue-Id: 2319D600011E X-Stat-Signature: wbfsr3ze3i4md5recm47fa1gmybg8jyc Received-SPF: none (infradead.org>: No applicable sender policy available) receiver=imf09; identity=mailfrom; envelope-from=""; helo=casper.infradead.org; client-ip=90.155.50.34 X-HE-DKIM-Result: pass/pass X-HE-Tag: 1617893497-477995 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 Thu, Apr 08, 2021 at 03:04:20PM +0100, David Howells wrote: > +static inline void set_page_private_2(struct page *page) > +{ > + get_page(page); > + SetPagePrivate2(page); PAGEFLAG(OwnerPriv1, owner_priv_1, PF_ANY) So we can set Private2 on any tail page ... > +void end_page_private_2(struct page *page) > +{ > + page = compound_head(page); > + VM_BUG_ON_PAGE(!PagePrivate2(page), page); > + clear_bit_unlock(PG_private_2, &page->flags); > + wake_up_page_bit(page, PG_private_2); ... but when we try to end on a tail, we actually wake up the head ... > +void wait_on_page_private_2(struct page *page) > +{ > + while (PagePrivate2(page)) > + wait_on_page_bit(page, PG_private_2); ... although if we were waiting on a tail, the wake up won't find us ... if only we had a way to ensure this kind of bug can't happen *cough, lend your support to the page folio patches*.