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 Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by smtp.lore.kernel.org (Postfix) with ESMTP id 95701C48260 for ; Tue, 6 Feb 2024 01:35:46 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id F39B76B0072; Mon, 5 Feb 2024 20:35:45 -0500 (EST) Received: by kanga.kvack.org (Postfix, from userid 40) id EE9A06B0074; Mon, 5 Feb 2024 20:35:45 -0500 (EST) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id DB0C66B0075; Mon, 5 Feb 2024 20:35:45 -0500 (EST) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0010.hostedemail.com [216.40.44.10]) by kanga.kvack.org (Postfix) with ESMTP id CB7ED6B0072 for ; Mon, 5 Feb 2024 20:35:45 -0500 (EST) Received: from smtpin30.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay09.hostedemail.com (Postfix) with ESMTP id 68F4B803A0 for ; Tue, 6 Feb 2024 01:35:45 +0000 (UTC) X-FDA: 81759662250.30.A7B260F Received: from mgamail.intel.com (mgamail.intel.com [198.175.65.10]) by imf24.hostedemail.com (Postfix) with ESMTP id 04A9018000D for ; Tue, 6 Feb 2024 01:35:42 +0000 (UTC) Authentication-Results: imf24.hostedemail.com; dkim=pass header.d=intel.com header.s=Intel header.b=mSAyjNFJ; dmarc=pass (policy=none) header.from=intel.com; spf=pass (imf24.hostedemail.com: domain of ying.huang@intel.com designates 198.175.65.10 as permitted sender) smtp.mailfrom=ying.huang@intel.com ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1707183343; h=from:from:sender:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-type:content-transfer-encoding: in-reply-to:in-reply-to:references:references:dkim-signature; bh=wsj8a1mvV3PEtdPg0gmr1ZPDC77ZadvhOKgL+BKTyqU=; b=C3uJzaNLZIIpiHAa5MCKGl3sSAGO/+DGM25lpkyA5S3gCIuBJikGB+JfzjRAr5lrw5HF6H ciUOgt/2GetB+3vdDzdQevXSd7ThTMqY5x9fU6RboKt2HNOkSH6xPnhom6NMwYnCZgyoI5 flOkhoHpsk342GPblihTGfoJ5m9dCoU= ARC-Authentication-Results: i=1; imf24.hostedemail.com; dkim=pass header.d=intel.com header.s=Intel header.b=mSAyjNFJ; dmarc=pass (policy=none) header.from=intel.com; spf=pass (imf24.hostedemail.com: domain of ying.huang@intel.com designates 198.175.65.10 as permitted sender) smtp.mailfrom=ying.huang@intel.com ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1707183343; a=rsa-sha256; cv=none; b=ejvXRjJk5LxjMnCf/tdPSO6KMciJ3Jlg+1mC6960FpZEgq70j5UvDHCKgpB4/ucSCWdrxO 2uxM41dRG/JvS3DEphjSzVFTmfWQV1CrBEB5BGBr1j4FwFpb9yl/b8OGoqY0XrA5pLIAHb xnZaM7FN8Fy85HP98v3eUS1Vto1D3iw= DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=intel.com; i=@intel.com; q=dns/txt; s=Intel; t=1707183343; x=1738719343; h=from:to:cc:subject:in-reply-to:references:date: message-id:mime-version; bh=TdErOC3oBHrD3EqLQL/DmWpuLadgOHm4vmA2o+l7M2I=; b=mSAyjNFJsuX1HvAGnRYDoTuCwAoPvD0hYIBbachtC9pQfxT9wwHzKL8l TWjk5vvHpPdcqbfyDkmDwrc47xpMD93X9iYM+3545eU9iuuu7lIItfU5H QJsQtb/FU51NlWiP10ezwAzUF7wUR6nHVG3Ep1GyBXEb6umGEB6euLLus apSpHV2XHYUwacaY4HTh9GOEVcNbpYnegwNft90fVisuZ+pRnGMlfBK0v yJKydRXxFR+56mP+OzE64YU+f4WykyUbptb1VVtnzkKJv3qe5bzsQJqBa zNrEpgHt6lAoLg0HIfLH3o0JSoBEvI714t+5olvYE2PvjM5antt3WmST0 A==; X-IronPort-AV: E=McAfee;i="6600,9927,10975"; a="18071359" X-IronPort-AV: E=Sophos;i="6.05,245,1701158400"; d="scan'208";a="18071359" Received: from fmviesa007.fm.intel.com ([10.60.135.147]) by orvoesa102.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 05 Feb 2024 17:35:41 -0800 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="6.05,245,1701158400"; d="scan'208";a="928850" Received: from yhuang6-desk2.sh.intel.com (HELO yhuang6-desk2.ccr.corp.intel.com) ([10.238.208.55]) by fmviesa007-auth.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 05 Feb 2024 17:35:38 -0800 From: "Huang, Ying" To: Kairui Song Cc: linux-mm@kvack.org, Kairui Song , Andrew Morton , Chris Li , Minchan Kim , Hugh Dickins , Johannes Weiner , Matthew Wilcox , Michal Hocko , Yosry Ahmed , David Hildenbrand , Yu Zhao , linux-kernel@vger.kernel.org Subject: Re: [PATCH] mm/swap: fix race condition in direct swapin path In-Reply-To: <20240205110959.4021-1-ryncsn@gmail.com> (Kairui Song's message of "Mon, 5 Feb 2024 19:09:59 +0800") References: <20240205110959.4021-1-ryncsn@gmail.com> Date: Tue, 06 Feb 2024 09:33:41 +0800 Message-ID: <871q9q1imi.fsf@yhuang6-desk2.ccr.corp.intel.com> User-Agent: Gnus/5.13 (Gnus v5.13) MIME-Version: 1.0 Content-Type: text/plain; charset=ascii X-Rspam-User: X-Stat-Signature: htqmn5yi9xb948i3omcg8m38q4ttwpf4 X-Rspamd-Server: rspam07 X-Rspamd-Queue-Id: 04A9018000D X-HE-Tag: 1707183342-600974 X-HE-Meta: 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 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: List-Subscribe: List-Unsubscribe: Kairui Song writes: > From: Kairui Song > > In the direct swapin path, when two or more threads swapin the same entry > at the same time, they get different pages (A, B) because swap cache is > skipped. Before one thread (T0) finishes the swapin and installs page (A) > to the PTE, another thread (T1) could finish swapin of page (B), > swap_free the entry, then modify and swap-out the page again, using the > same entry. It break the pte_same check because PTE value is unchanged, > causing ABA problem. Then thread (T0) will then install the stalled page > (A) into the PTE so new data in page (B) is lost, one possible callstack > is like this: > > CPU0 CPU1 > ---- ---- > do_swap_page() do_swap_page() with same entry > > > swap_readpage() <- read to page A swap_readpage() <- read to page B > > ... set_pte_at() > swap_free() <- Now the entry is freed. > > > pte_same() <- Check pass, PTE seems > unchanged, but page A > is stalled! > swap_free() <- page B content lost! > set_pte_at() <- staled page A installed! > > To fix this, reuse swapcache_prepare which will pin the swap entry using > the cache flag, and allow only one thread to pin it. Release the pin > after PT unlocked. Racers will simply busy wait since it's a rare > and very short event. > > Other methods like increasing the swap count don't seem to be a good > idea after some tests, that will cause racers to fall back to the > cached swapin path, two swapin path being used at the same time > leads to a much more complex scenario. > > Reproducer: > > This race issue can be triggered easily using a well constructed > reproducer and patched brd (with a delay in read path) [1]: > > With latest 6.8 mainline, race caused data loss can be observed easily: > $ gcc -g -lpthread test-thread-swap-race.c && ./a.out > Polulating 32MB of memory region... > Keep swapping out... > Starting round 0... > Spawning 65536 workers... > 32746 workers spawned, wait for done... > Round 0: Error on 0x5aa00, expected 32746, got 32743, 3 data loss! > Round 0: Error on 0x395200, expected 32746, got 32743, 3 data loss! > Round 0: Error on 0x3fd000, expected 32746, got 32737, 9 data loss! > Round 0 Failed, 15 data loss! > > This reproducer spawns multiple threads sharing the same memory region > using a small swap device. Every two threads updates mapped pages one by > one in opposite direction trying to create a race, with one dedicated > thread keep swapping out the data out using madvise. > > The reproducer created a reproduce rate of about once every 5 minutes, > so the race should be totally possible in production. > > After this patch, I ran the reproducer for over a few hundred rounds > and no data loss observed. > > Performance overhead is minimal, microbenchmark swapin 10G from 32G > zram: > > Before: 10934698 us > After: 11157121 us > Non-direct: 13155355 us (Dropping SWP_SYNCHRONOUS_IO flag) > > Fixes: 0bcac06f27d7 ("mm, swap: skip swapcache for swapin of synchronous device") > Link: https://github.com/ryncsn/emm-test-project/tree/master/swap-stress-race [1] > Signed-off-by: Kairui Song Reported-by: "Huang, Ying" > --- > Huge thanks to Huang Ying and Chris Li for help finding this issue! > > mm/memory.c | 19 +++++++++++++++++++ > mm/swap.h | 5 +++++ > mm/swapfile.c | 16 ++++++++++++++++ > 3 files changed, 40 insertions(+) > > diff --git a/mm/memory.c b/mm/memory.c > index 7e1f4849463a..fd7c55a292f1 100644 > --- a/mm/memory.c > +++ b/mm/memory.c > @@ -3867,6 +3867,20 @@ vm_fault_t do_swap_page(struct vm_fault *vmf) > if (!folio) { > if (data_race(si->flags & SWP_SYNCHRONOUS_IO) && > __swap_count(entry) == 1) { > + /* > + * With swap count == 1, after we read the entry, > + * other threads could finish swapin first, free > + * the entry, then swapout the modified page using > + * the same entry. Now the content we just read is > + * stalled, and it's undetectable as pte_same() > + * returns true due to entry reuse. > + * > + * So pin the swap entry using the cache flag even "pin" doesn't sound intuitive here. I know that the swap entry will not be freed with this. But now, the parallel swap in will busy waiting. So, I suggest to say, Prevent parallel swapin from proceeding with the cache flag. Otherwise, it may swapin first, free the entry, then swapout the modified page using the same entry ... > + * cache is not used. > + */ > + if (swapcache_prepare(entry)) > + goto out; > + > /* skip swapcache */ > folio = vma_alloc_folio(GFP_HIGHUSER_MOVABLE, 0, > vma, vmf->address, false); > @@ -4116,6 +4130,9 @@ vm_fault_t do_swap_page(struct vm_fault *vmf) > unlock: > if (vmf->pte) > pte_unmap_unlock(vmf->pte, vmf->ptl); > + /* Clear the swap cache pin for direct swapin after PTL unlock */ > + if (folio && !swapcache) > + swapcache_clear(si, entry); > out: > if (si) > put_swap_device(si); > @@ -4124,6 +4141,8 @@ vm_fault_t do_swap_page(struct vm_fault *vmf) > if (vmf->pte) > pte_unmap_unlock(vmf->pte, vmf->ptl); > out_page: > + if (!swapcache) > + swapcache_clear(si, entry); > folio_unlock(folio); > out_release: > folio_put(folio); > diff --git a/mm/swap.h b/mm/swap.h > index 758c46ca671e..fc2f6ade7f80 100644 > --- a/mm/swap.h > +++ b/mm/swap.h > @@ -41,6 +41,7 @@ void __delete_from_swap_cache(struct folio *folio, > void delete_from_swap_cache(struct folio *folio); > void clear_shadow_from_swap_cache(int type, unsigned long begin, > unsigned long end); > +void swapcache_clear(struct swap_info_struct *si, swp_entry_t entry); > struct folio *swap_cache_get_folio(swp_entry_t entry, > struct vm_area_struct *vma, unsigned long addr); > struct folio *filemap_get_incore_folio(struct address_space *mapping, > @@ -97,6 +98,10 @@ static inline int swap_writepage(struct page *p, struct writeback_control *wbc) > return 0; > } > > +static inline void swapcache_clear(struct swap_info_struct *si, swp_entry_t entry) > +{ > +} > + > static inline struct folio *swap_cache_get_folio(swp_entry_t entry, > struct vm_area_struct *vma, unsigned long addr) > { > diff --git a/mm/swapfile.c b/mm/swapfile.c > index 556ff7347d5f..f7d4ad152a7f 100644 > --- a/mm/swapfile.c > +++ b/mm/swapfile.c > @@ -3365,6 +3365,22 @@ int swapcache_prepare(swp_entry_t entry) > return __swap_duplicate(entry, SWAP_HAS_CACHE); > } > > +/* > + * Clear the cache flag and release pinned entry. Even if we will keep "pin" in above comments, this is hard to be understood for reader. Need a little more explanation like "release pinned entry for device with SWP_SYNCHRONOUS_IO. Or, just remove the comments. We have comments in calling site already. > + */ > +void swapcache_clear(struct swap_info_struct *si, swp_entry_t entry) > +{ > + struct swap_cluster_info *ci; > + unsigned long offset = swp_offset(entry); > + unsigned char usage; > + > + ci = lock_cluster_or_swap_info(si, offset); > + usage = __swap_entry_free_locked(si, offset, SWAP_HAS_CACHE); > + unlock_cluster_or_swap_info(si, ci); > + if (!usage) > + free_swap_slot(entry); > +} > + > struct swap_info_struct *swp_swap_info(swp_entry_t entry) > { > return swap_type_to_swap_info(swp_type(entry)); Otherwise it looks good for me, Thanks! Reviewed-by: "Huang, Ying"