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 X-Spam-Level: X-Spam-Status: No, score=-9.6 required=3.0 tests=DKIM_INVALID,DKIM_SIGNED, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY, SPF_HELO_NONE,SPF_PASS,USER_AGENT_GIT autolearn=unavailable autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 3F486C7618B for ; Wed, 24 Jul 2019 06:53:31 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 10E35218DA for ; Wed, 24 Jul 2019 06:53:31 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=fail reason="signature verification failed" (2048-bit key) header.d=infradead.org header.i=@infradead.org header.b="gHoA3rLx" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726607AbfGXGx3 (ORCPT ); Wed, 24 Jul 2019 02:53:29 -0400 Received: from bombadil.infradead.org ([198.137.202.133]:39378 "EHLO bombadil.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726559AbfGXGx1 (ORCPT ); Wed, 24 Jul 2019 02:53:27 -0400 DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=bombadil.20170209; h=Content-Transfer-Encoding: MIME-Version:References:In-Reply-To:Message-Id:Date:Subject:Cc:To:From:Sender :Reply-To:Content-Type: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=jUagJle8tiqkx+fZcCE6Gfny4t7Azmd0YxZDCEv72fs=; b=gHoA3rLxbbBb8a0isoL8eqDuAd 5No71pHNiivV7f+CSgnKf/BnSlSNK6IHFCeFwtrWSRDbAHPCPDE3FP1zsCfMsYxHtJ90yYDlUxj2K HsjlpGb+HBDiw4pJkfZUt0rZPL3rR+vVkgO7MQ7aFVnbJ/dH6yr+BPTKxF7wdx1yMwjk0nxNfGN5a MeLw7sIA4cVOQlsewuFjuZ1oKKhb+BnYot7yxvtYabgThfnIv5HDf78+WbsMXOcknLuY5xH2VoJDX QIF4jW0Vtaeu3JTdStE89iThn0BlxErxbbHeDGs5EIrl76zsfFj/jdn5E2iKTaq3FlbL16zEG+dDX j7FGDjGg==; Received: from 089144207240.atnat0016.highway.bob.at ([89.144.207.240] helo=localhost) by bombadil.infradead.org with esmtpsa (Exim 4.92 #3 (Red Hat Linux)) id 1hqB9P-0004Mo-Lp; Wed, 24 Jul 2019 06:53:24 +0000 From: Christoph Hellwig To: =?UTF-8?q?J=C3=A9r=C3=B4me=20Glisse?= , Jason Gunthorpe , Ben Skeggs Cc: Ralph Campbell , linux-mm@kvack.org, nouveau@lists.freedesktop.org, dri-devel@lists.freedesktop.org, linux-kernel@vger.kernel.org Subject: [PATCH 7/7] mm: comment on VM_FAULT_RETRY semantics in handle_mm_fault Date: Wed, 24 Jul 2019 08:52:58 +0200 Message-Id: <20190724065258.16603-8-hch@lst.de> X-Mailer: git-send-email 2.20.1 In-Reply-To: <20190724065258.16603-1-hch@lst.de> References: <20190724065258.16603-1-hch@lst.de> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-SRS-Rewrite: SMTP reverse-path rewritten from by bombadil.infradead.org. See http://www.infradead.org/rpr.html Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Jason Gunthorpe The magic dropping of mmap_sem when handle_mm_fault returns VM_FAULT_RETRY is rather subtile. Add a comment explaining it. Signed-off-by: Jason Gunthorpe [hch: wrote a changelog] Signed-off-by: Christoph Hellwig --- mm/hmm.c | 4 +++- 1 file changed, 3 insertions(+), 1 deletion(-) diff --git a/mm/hmm.c b/mm/hmm.c index 16b6731a34db..54b3a4162ae9 100644 --- a/mm/hmm.c +++ b/mm/hmm.c @@ -301,8 +301,10 @@ static int hmm_vma_do_fault(struct mm_walk *walk, unsigned long addr, flags |= hmm_vma_walk->block ? 0 : FAULT_FLAG_ALLOW_RETRY; flags |= write_fault ? FAULT_FLAG_WRITE : 0; ret = handle_mm_fault(vma, addr, flags); - if (ret & VM_FAULT_RETRY) + if (ret & VM_FAULT_RETRY) { + /* Note, handle_mm_fault did up_read(&mm->mmap_sem)) */ return -EAGAIN; + } if (ret & VM_FAULT_ERROR) { *pfn = range->values[HMM_PFN_ERROR]; return -EFAULT; -- 2.20.1