From patchwork Tue Feb 11 03:01:34 2020 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Qian Cai X-Patchwork-Id: 11374723 Return-Path: Received: from mail.kernel.org (pdx-korg-mail-1.web.codeaurora.org [172.30.200.123]) by pdx-korg-patchwork-2.web.codeaurora.org (Postfix) with ESMTP id 367FF924 for ; Tue, 11 Feb 2020 03:01:58 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id E968D20870 for ; Tue, 11 Feb 2020 03:01:57 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=fail reason="signature verification failed" (2048-bit key) header.d=lca.pw header.i=@lca.pw header.b="QdqXtOYR" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org E968D20870 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=lca.pw Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=owner-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix) id 1DAC96B026C; Mon, 10 Feb 2020 22:01:57 -0500 (EST) Delivered-To: linux-mm-outgoing@kvack.org Received: by kanga.kvack.org (Postfix, from userid 40) id 18B086B026D; Mon, 10 Feb 2020 22:01:57 -0500 (EST) X-Original-To: int-list-linux-mm@kvack.org X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 0A28D6B026E; Mon, 10 Feb 2020 22:01:57 -0500 (EST) X-Original-To: linux-mm@kvack.org X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0028.hostedemail.com [216.40.44.28]) by kanga.kvack.org (Postfix) with ESMTP id E6B9F6B026C for ; Mon, 10 Feb 2020 22:01:56 -0500 (EST) Received: from smtpin11.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay05.hostedemail.com (Postfix) with ESMTP id 74531181AEF00 for ; Tue, 11 Feb 2020 03:01:56 +0000 (UTC) X-FDA: 76476346632.11.star49_10b71c393c94c X-Spam-Summary: 2,0,0,c575f94684c0bbbf,d41d8cd98f00b204,cai@lca.pw,:akpm@linux-foundation.org:elver@google.com:willy@infradead.org::linux-kernel@vger.kernel.org:cai@lca.pw:kirill@shutemov.name,RULES_HIT:41:355:379:541:800:960:973:988:989:1260:1311:1314:1345:1437:1515:1535:1544:1711:1730:1747:1777:1792:2198:2199:2393:2559:2562:2693:2918:3138:3139:3140:3141:3142:3355:3865:3866:3867:3868:3870:3871:3872:4118:4321:4605:5007:6261:6653:7875:7903:7904:8784:8957:9163:10004:11026:11473:11658:11914:12043:12294:12296:12297:12438:12517:12519:12555:12679:12740:12895:12986:13894:14018:14096:14104:14181:14394:14721:21067:21080:21444:21451:21627:21990:30003:30029:30054:30056:30065:30070,0,RBL:209.85.222.196:@lca.pw:.lbl8.mailshell.net-62.14.0.100 66.201.201.201,CacheIP:none,Bayesian:0.5,0.5,0.5,Netcheck:none,DomainCache:0,MSF:not bulk,SPF:fp,MSBL:0,DNSBL:neutral,Custom_rules:0:0:0,LFtime:59,LUA_SUMMARY:none X-HE-Tag: star49_10b71c393c94c X-Filterd-Recvd-Size: 7117 Received: from mail-qk1-f196.google.com (mail-qk1-f196.google.com [209.85.222.196]) by imf23.hostedemail.com (Postfix) with ESMTP for ; Tue, 11 Feb 2020 03:01:54 +0000 (UTC) Received: by mail-qk1-f196.google.com with SMTP id v195so8745966qkb.11 for ; Mon, 10 Feb 2020 19:01:53 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=lca.pw; s=google; h=from:to:cc:subject:date:message-id:mime-version :content-transfer-encoding; bh=aDuKz8LG6e/Q6OjAADX6nh47gn2hXYEAHBLoIv0xEDo=; b=QdqXtOYRY6N8H8KoXWsYQuIDa5MloudL6cocwRCcO9e9jEeWtDY/GESCG5mAyybMvL PzcPSTjcl1i99pQUjxn7zEYH634CSw+jE1UF16LMtcu+NYRbTZXmUrswtiIicCRWhAYl NZjCeAhxrhZzKWF6bYFm4rqjy910Nlh60LnMTkjI+MUA3Zn5oQ984Dvev3I0A4D0agRm ffZVjuk8VvKsSmpTpUEF3MbU0hwul0SnEb3vKC1RDyBBxL5Op/FsNIz2WkPljsywQMlQ LpFj9wyu9QwcU2lqQbEl1Thvvfl8qghMv80IxM6aYZBTOMC8kJ+HxUD8P3iudv66P+ka TyVg== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:from:to:cc:subject:date:message-id:mime-version :content-transfer-encoding; bh=aDuKz8LG6e/Q6OjAADX6nh47gn2hXYEAHBLoIv0xEDo=; b=g0aaWnxkMDuR4vl+5RRikoo9DSwzAGQjMG3+vYvNuKeAb5vxp4/CU26LLSYj+/xTKJ slIlGDTk1zhgzbat5YSZOgEbPk3Sa6vvUjsG8Z0E6YNZgQMDmYje8a0O+veNHLXotLWr m11ElBj+o+5Y4iFeEz4UDb3fxO2PTS68ZKOO0xSzVN2Ec+hLANVlhyXtTkAcEBi3k8DX JHuxwzE9q2ZM9dFbfb4+b1JGc9PJqpAr/hSi4C7MXzMSolfwAIQRzRbAxxpGOlvk8DDO A2mxbUWvKp7txFDSoj0SKenVWlVk2q2bHtel3W4kPFai6aBYQ1rN+vaSDebTuFNGjM79 k9jg== X-Gm-Message-State: APjAAAV6ic+EtBiWKrFrZ2j3j0+zSpKCdS/cLcaNgXoDSRXvtEJiIYMf mcXDV9+YWFCdkNnRFPCrpozHsQ== X-Google-Smtp-Source: APXvYqwWgIBKHaGcKaZl3h0ngUDh7ttSd105xW5gy8kceaUNQbNSZx35PytD5R5FOB+GWeSxZPwKIg== X-Received: by 2002:a05:620a:1fa:: with SMTP id x26mr4439937qkn.311.1581390113130; Mon, 10 Feb 2020 19:01:53 -0800 (PST) Received: from ovpn-120-145.rdu2.redhat.com (pool-71-184-117-43.bstnma.fios.verizon.net. [71.184.117.43]) by smtp.gmail.com with ESMTPSA id h13sm1232613qtu.23.2020.02.10.19.01.52 (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Mon, 10 Feb 2020 19:01:52 -0800 (PST) From: Qian Cai To: akpm@linux-foundation.org Cc: elver@google.com, willy@infradead.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, Qian Cai , "Kirill A . Shutemov" Subject: [PATCH v2] mm/filemap: fix a data race in filemap_fault() Date: Mon, 10 Feb 2020 22:01:34 -0500 Message-Id: <20200211030134.1847-1-cai@lca.pw> X-Mailer: git-send-email 2.21.0 (Apple Git-122.2) MIME-Version: 1.0 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: struct file_ra_state ra.mmap_miss could be accessed concurrently during page faults as noticed by KCSAN, BUG: KCSAN: data-race in filemap_fault / filemap_map_pages write to 0xffff9b1700a2c1b4 of 4 bytes by task 3292 on cpu 30: filemap_fault+0x920/0xfc0 do_sync_mmap_readahead at mm/filemap.c:2384 (inlined by) filemap_fault at mm/filemap.c:2486 __xfs_filemap_fault+0x112/0x3e0 [xfs] xfs_filemap_fault+0x74/0x90 [xfs] __do_fault+0x9e/0x220 do_fault+0x4a0/0x920 __handle_mm_fault+0xc69/0xd00 handle_mm_fault+0xfc/0x2f0 do_page_fault+0x263/0x6f9 page_fault+0x34/0x40 read to 0xffff9b1700a2c1b4 of 4 bytes by task 3313 on cpu 32: filemap_map_pages+0xc2e/0xd80 filemap_map_pages at mm/filemap.c:2625 do_fault+0x3da/0x920 __handle_mm_fault+0xc69/0xd00 handle_mm_fault+0xfc/0x2f0 do_page_fault+0x263/0x6f9 page_fault+0x34/0x40 Reported by Kernel Concurrency Sanitizer on: CPU: 32 PID: 3313 Comm: systemd-udevd Tainted: G W L 5.5.0-next-20200210+ #1 Hardware name: HPE ProLiant DL385 Gen10/ProLiant DL385 Gen10, BIOS A40 07/10/2019 ra.mmap_miss is used to contribute the readahead decisions, a data race could be undesirable. Both the read and write is only under non-exclusive mmap_sem, two concurrent writers could even overflow the counter. Fixing the underflow by writing to a local variable before committing a final store to ra.mmap_miss given a small inaccuracy of the counter should be acceptable. Suggested-by: Kirill A. Shutemov Signed-off-by: Qian Cai Signed-off-by: Kirill A. Shutemov Tested-by: Qian Cai Reviewed-by: Matthew Wilcox (Oracle) Signed-off-by: Kirill A. Shutemov --- v2: fix the underflow issue pointed out by Matthew. mm/filemap.c | 20 +++++++++++++------- 1 file changed, 13 insertions(+), 7 deletions(-) diff --git a/mm/filemap.c b/mm/filemap.c index 1784478270e1..2e298db2e80f 100644 --- a/mm/filemap.c +++ b/mm/filemap.c @@ -2365,6 +2365,7 @@ static struct file *do_sync_mmap_readahead(struct vm_fault *vmf) struct address_space *mapping = file->f_mapping; struct file *fpin = NULL; pgoff_t offset = vmf->pgoff; + unsigned int mmap_miss; /* If we don't want any read-ahead, don't bother */ if (vmf->vma->vm_flags & VM_RAND_READ) @@ -2380,14 +2381,15 @@ static struct file *do_sync_mmap_readahead(struct vm_fault *vmf) } /* Avoid banging the cache line if not needed */ - if (ra->mmap_miss < MMAP_LOTSAMISS * 10) - ra->mmap_miss++; + mmap_miss = READ_ONCE(ra->mmap_miss); + if (mmap_miss < MMAP_LOTSAMISS * 10) + WRITE_ONCE(ra->mmap_miss, ++mmap_miss); /* * Do we miss much more than hit in this file? If so, * stop bothering with read-ahead. It will only hurt. */ - if (ra->mmap_miss > MMAP_LOTSAMISS) + if (mmap_miss > MMAP_LOTSAMISS) return fpin; /* @@ -2413,13 +2415,15 @@ static struct file *do_async_mmap_readahead(struct vm_fault *vmf, struct file_ra_state *ra = &file->f_ra; struct address_space *mapping = file->f_mapping; struct file *fpin = NULL; + unsigned int mmap_miss; pgoff_t offset = vmf->pgoff; /* If we don't want any read-ahead, don't bother */ if (vmf->vma->vm_flags & VM_RAND_READ) return fpin; - if (ra->mmap_miss > 0) - ra->mmap_miss--; + mmap_miss = READ_ONCE(ra->mmap_miss); + if (mmap_miss) + WRITE_ONCE(ra->mmap_miss, --mmap_miss); if (PageReadahead(page)) { fpin = maybe_unlock_mmap_for_io(vmf, fpin); page_cache_async_readahead(mapping, ra, file, @@ -2586,6 +2590,7 @@ void filemap_map_pages(struct vm_fault *vmf, unsigned long max_idx; XA_STATE(xas, &mapping->i_pages, start_pgoff); struct page *page; + unsigned int mmap_miss = READ_ONCE(file->f_ra.mmap_miss); rcu_read_lock(); xas_for_each(&xas, page, end_pgoff) { @@ -2622,8 +2627,8 @@ void filemap_map_pages(struct vm_fault *vmf, if (page->index >= max_idx) goto unlock; - if (file->f_ra.mmap_miss > 0) - file->f_ra.mmap_miss--; + if (mmap_miss > 0) + mmap_miss--; vmf->address += (xas.xa_index - last_pgoff) << PAGE_SHIFT; if (vmf->pte) @@ -2643,6 +2648,7 @@ void filemap_map_pages(struct vm_fault *vmf, break; } rcu_read_unlock(); + WRITE_ONCE(file->f_ra.mmap_miss, mmap_miss); } EXPORT_SYMBOL(filemap_map_pages);