From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pf0-f197.google.com (mail-pf0-f197.google.com [209.85.192.197]) by kanga.kvack.org (Postfix) with ESMTP id B91E06B0005 for ; Wed, 30 May 2018 06:27:55 -0400 (EDT) Received: by mail-pf0-f197.google.com with SMTP id e3-v6so10687732pfe.15 for ; Wed, 30 May 2018 03:27:55 -0700 (PDT) Received: from mga17.intel.com (mga17.intel.com. [192.55.52.151]) by mx.google.com with ESMTPS id x14-v6si8510410pll.37.2018.05.30.03.27.54 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Wed, 30 May 2018 03:27:54 -0700 (PDT) Date: Wed, 30 May 2018 13:27:50 +0300 From: "Kirill A. Shutemov" Subject: Re: [PATCH] mm/huge_memory.c: __split_huge_page() use atomic ClearPageDirty() Message-ID: <20180530102750.6mmlmypt35w4xaei@black.fi.intel.com> References: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Sender: owner-linux-mm@kvack.org List-ID: To: Hugh Dickins Cc: Andrew Morton , Konstantin Khlebnikov , Nicholas Piggin , linux-kernel@vger.kernel.org, linux-mm@kvack.org On Wed, May 30, 2018 at 01:50:22AM +0000, Hugh Dickins wrote: > Swapping load on huge=always tmpfs (with khugepaged tuned up to be very > eager, but I'm not sure that is relevant) soon hung uninterruptibly, > waiting for page lock in shmem_getpage_gfp()'s find_lock_entry(), most > often when "cp -a" was trying to write to a smallish file. Debug showed > that the page in question was not locked, and page->mapping NULL by now, > but page->index consistent with having been in a huge page before. > > Reproduced in minutes on a 4.15 kernel, even with 4.17's 605ca5ede764 > ("mm/huge_memory.c: reorder operations in __split_huge_page_tail()") > added in; but took hours to reproduce on a 4.17 kernel (no idea why). > > The culprit proved to be the __ClearPageDirty() on tails beyond i_size > in __split_huge_page(): the non-atomic __bitoperation may have been safe > when 4.8's baa355fd3314 ("thp: file pages support for split_huge_page()") > introduced it, but liable to erase PageWaiters after 4.10's 62906027091f > ("mm: add PageWaiters indicating tasks are waiting for a page bit"). > > Fixes: 62906027091f ("mm: add PageWaiters indicating tasks are waiting for a page bit") > Signed-off-by: Hugh Dickins Thanks for catching this. Acked-by: Kirill A. Shutemov -- Kirill A. Shutemov