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x-ptr=pass x-ptr-helo=vger.kernel.org x-ptr-lookup=vger.kernel.org; x-return-mx=pass smtp.domain=vger.kernel.org smtp.result=pass smtp_org.domain=kernel.org smtp_org.result=pass smtp_is_org_domain=no header.domain=kernel.org header.result=pass header_is_org_domain=yes Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1750986AbeBHKSA (ORCPT ); Thu, 8 Feb 2018 05:18:00 -0500 Received: from mail-oi0-f67.google.com ([209.85.218.67]:44890 "EHLO mail-oi0-f67.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750877AbeBHKR6 (ORCPT ); Thu, 8 Feb 2018 05:17:58 -0500 X-Google-Smtp-Source: AH8x227R1nyHV1LVFuFrTX5h6iSgNM0oKDlhOzJi6eB34LfoV0k/CrEd2SVQkehx0BPKlTTE5q6lhQ== Date: Thu, 8 Feb 2018 02:17:52 -0800 From: Minchan Kim To: "Huang, Ying" Cc: Andrew Morton , linux-mm@kvack.org, linux-kernel@vger.kernel.org, Huang Ying , Konrad Rzeszutek Wilk , Dan Streetman , Seth Jennings , Tetsuo Handa , Shaohua Li , Michal Hocko , Johannes Weiner , Mel Gorman , Shakeel Butt , stable@vger.kernel.org, Sergey Senozhatsky Subject: Re: [PATCH -mm -v2] mm, swap, frontswap: Fix THP swap if frontswap enabled Message-ID: <20180208101752.GA74192@eng-minchan1.roam.corp.google.com> References: <20180207070035.30302-1-ying.huang@intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20180207070035.30302-1-ying.huang@intel.com> User-Agent: Mutt/1.9.2 (2017-12-15) Sender: stable-owner@vger.kernel.org X-Mailing-List: stable@vger.kernel.org X-getmail-retrieved-from-mailbox: INBOX X-Mailing-List: linux-kernel@vger.kernel.org List-ID: On Wed, Feb 07, 2018 at 03:00:35PM +0800, Huang, Ying wrote: > From: Huang Ying > > It was reported by Sergey Senozhatsky that if THP (Transparent Huge > Page) and frontswap (via zswap) are both enabled, when memory goes low > so that swap is triggered, segfault and memory corruption will occur > in random user space applications as follow, > > kernel: urxvt[338]: segfault at 20 ip 00007fc08889ae0d sp 00007ffc73a7fc40 error 6 in libc-2.26.so[7fc08881a000+1ae000] > #0 0x00007fc08889ae0d _int_malloc (libc.so.6) > #1 0x00007fc08889c2f3 malloc (libc.so.6) > #2 0x0000560e6004bff7 _Z14rxvt_wcstoutf8PKwi (urxvt) > #3 0x0000560e6005e75c n/a (urxvt) > #4 0x0000560e6007d9f1 _ZN16rxvt_perl_interp6invokeEP9rxvt_term9hook_typez (urxvt) > #5 0x0000560e6003d988 _ZN9rxvt_term9cmd_parseEv (urxvt) > #6 0x0000560e60042804 _ZN9rxvt_term6pty_cbERN2ev2ioEi (urxvt) > #7 0x0000560e6005c10f _Z17ev_invoke_pendingv (urxvt) > #8 0x0000560e6005cb55 ev_run (urxvt) > #9 0x0000560e6003b9b9 main (urxvt) > #10 0x00007fc08883af4a __libc_start_main (libc.so.6) > #11 0x0000560e6003f9da _start (urxvt) > > After bisection, it was found the first bad commit is > bd4c82c22c367e068 ("mm, THP, swap: delay splitting THP after swapped > out"). > > The root cause is as follow. > > When the pages are written to swap device during swapping out in > swap_writepage(), zswap (fontswap) is tried to compress the pages > instead to improve the performance. But zswap (frontswap) will treat > THP as normal page, so only the head page is saved. After swapping > in, tail pages will not be restored to its original contents, so cause > the memory corruption in the applications. > > This is fixed via splitting THP before writing the page to swap device > if frontswap is enabled. To deal with the situation where frontswap > is enabled at runtime, whether the page is THP is checked before using > frontswap during swapping out too. > > Reported-and-tested-by: Sergey Senozhatsky > Signed-off-by: "Huang, Ying" > Cc: Konrad Rzeszutek Wilk > Cc: Dan Streetman > Cc: Seth Jennings > Cc: Minchan Kim > Cc: Tetsuo Handa > Cc: Shaohua Li > Cc: Michal Hocko > Cc: Johannes Weiner > Cc: Mel Gorman > Cc: Shakeel Butt > Cc: stable@vger.kernel.org # 4.14 > Fixes: bd4c82c22c367e068 ("mm, THP, swap: delay splitting THP after swapped out") > > Changelog: > > v2: > > - Move frontswap check into swapfile.c to avoid to make vmscan.c > depends on frontswap. > --- > mm/page_io.c | 2 +- > mm/swapfile.c | 3 +++ > 2 files changed, 4 insertions(+), 1 deletion(-) > > diff --git a/mm/page_io.c b/mm/page_io.c > index b41cf9644585..6dca817ae7a0 100644 > --- a/mm/page_io.c > +++ b/mm/page_io.c > @@ -250,7 +250,7 @@ int swap_writepage(struct page *page, struct writeback_control *wbc) > unlock_page(page); > goto out; > } > - if (frontswap_store(page) == 0) { > + if (!PageTransHuge(page) && frontswap_store(page) == 0) { Why do we need this? If frontswap_enabled is enabled but it doesn't support THP, it doesn't allow cluster allocation by below logic so any THP page shouldn't come this path. What do I missing now? > set_page_writeback(page); > unlock_page(page); > end_page_writeback(page); > diff --git a/mm/swapfile.c b/mm/swapfile.c > index 006047b16814..0b7c7883ce64 100644 > --- a/mm/swapfile.c > +++ b/mm/swapfile.c > @@ -934,6 +934,9 @@ int get_swap_pages(int n_goal, bool cluster, swp_entry_t swp_entries[]) > > /* Only single cluster request supported */ > WARN_ON_ONCE(n_goal > 1 && cluster); > + /* Frontswap doesn't support THP */ > + if (frontswap_enabled() && cluster) > + goto noswap; > > avail_pgs = atomic_long_read(&nr_swap_pages) / nr_pages; > if (avail_pgs <= 0) > -- > 2.15.1 >