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[2607:7c80:54:e::133]) by mx.google.com with ESMTPS id l8si2919740pgk.528.2019.06.19.04.54.27 for (version=TLS1_3 cipher=AEAD-AES256-GCM-SHA384 bits=256/256); Wed, 19 Jun 2019 04:54:27 -0700 (PDT) Received-SPF: pass (google.com: best guess record for domain of batv+77cd4ac56e5e79ab4dbe+5778+infradead.org+hch@bombadil.srs.infradead.org designates 2607:7c80:54:e::133 as permitted sender) client-ip=2607:7c80:54:e::133; Authentication-Results: mx.google.com; dkim=pass header.i=@infradead.org header.s=bombadil.20170209 header.b=k0xGPIpK; spf=pass (google.com: best guess record for domain of batv+77cd4ac56e5e79ab4dbe+5778+infradead.org+hch@bombadil.srs.infradead.org designates 2607:7c80:54:e::133 as permitted sender) smtp.mailfrom=BATV+77cd4ac56e5e79ab4dbe+5778+infradead.org+hch@bombadil.srs.infradead.org DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=bombadil.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:Resent-Date: Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Id: List-Help:List-Unsubscribe:List-Subscribe:List-Post:List-Owner:List-Archive; bh=ZMXqazDQazrKKSlfFDYmUFpilZIibnGHtDfXdH5dHKE=; b=k0xGPIpKWDBE1uNoMaB6BA8Rj J14iEyyGUyAtE4tSq7WhsgKGCuRN9es82gkxyNp9nSgEg7726Fp5Q6j8njKnjZw1TL2kIzgkhhW/B KNeWruWnKckQqgS6VEq6LV0yJnSYlTho5MCkjXZAbyoi1aFDSWffvabKy9p1PRMW4YP8nhrqvgXZe EB7qiBw+50HfBshE8hvrxSxfpGqjP4LVX2zgDyH8wUfEe3zTn3IN+1WKe21I1yyVcdCz3X5t8c3G0 chcINAU+cS2mR0PgkXz7kwPZ6jT4aWdw4B+PfSbOUGeJagOxjTH/Ku4GUj/Cvtahzx7Xje2r6IiHm EK+xNL6wQ==; Received: from hch by bombadil.infradead.org with local (Exim 4.92 #3 (Red Hat Linux)) id 1hdZAU-0004pM-0A; Wed, 19 Jun 2019 11:54:22 +0000 Date: Wed, 19 Jun 2019 04:54:21 -0700 From: Christoph Hellwig To: Jason Gunthorpe Cc: Christoph Hellwig , Jerome Glisse , Ralph Campbell , John Hubbard , Felix.Kuehling@amd.com, linux-rdma@vger.kernel.org, linux-mm@kvack.org, Andrea Arcangeli , dri-devel@lists.freedesktop.org, amd-gfx@lists.freedesktop.org, Ben Skeggs , Philip Yang Subject: Re: [PATCH v3 hmm 06/12] mm/hmm: Hold on to the mmget for the lifetime of the range Message-ID: <20190619115421.GB19138@infradead.org> References: <20190614004450.20252-1-jgg@ziepe.ca> <20190614004450.20252-7-jgg@ziepe.ca> <20190615141435.GF17724@infradead.org> <20190618151100.GI6961@ziepe.ca> <20190619081858.GB24900@infradead.org> <20190619113452.GB9360@ziepe.ca> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20190619113452.GB9360@ziepe.ca> User-Agent: Mutt/1.11.4 (2019-03-13) X-SRS-Rewrite: SMTP reverse-path rewritten from by bombadil.infradead.org. See http://www.infradead.org/rpr.html 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 Wed, Jun 19, 2019 at 08:34:52AM -0300, Jason Gunthorpe wrote: > /** > * list_empty_careful - tests whether a list is empty and not being modified > * @head: the list to test > * > * Description: > * tests whether a list is empty _and_ checks that no other CPU might be > * in the process of modifying either member (next or prev) > * > * NOTE: using list_empty_careful() without synchronization > * can only be safe if the only activity that can happen > * to the list entry is list_del_init(). Eg. it cannot be used > * if another CPU could re-list_add() it. > */ > > Agree it doesn't seem obvious why this is relevant when checking the > list head.. > > Maybe the comment is a bit misleading? >From looking at the commit log in the history tree list_empty_careful was initially added by Linus, and then mingo added that comment later. I don't see how list_del_init would change anything here, so I suspect list_del_init was just used as a short hand for list_del or list_del_init.