From patchwork Wed Jul 10 19:28:16 2019 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Tejun Heo X-Patchwork-Id: 11038857 Return-Path: Received: from mail.wl.linuxfoundation.org (pdx-wl-mail.web.codeaurora.org [172.30.200.125]) by pdx-korg-patchwork-2.web.codeaurora.org (Postfix) with ESMTP id E9BB91395 for ; Wed, 10 Jul 2019 19:28:47 +0000 (UTC) Received: from mail.wl.linuxfoundation.org (localhost [127.0.0.1]) by mail.wl.linuxfoundation.org (Postfix) with ESMTP id D85DA202A5 for ; Wed, 10 Jul 2019 19:28:47 +0000 (UTC) Received: by mail.wl.linuxfoundation.org (Postfix, from userid 486) id CC8062873C; Wed, 10 Jul 2019 19:28:47 +0000 (UTC) X-Spam-Checker-Version: SpamAssassin 3.3.1 (2010-03-16) on pdx-wl-mail.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-7.7 required=2.0 tests=BAYES_00,DKIM_INVALID, DKIM_SIGNED,MAILING_LIST_MULTI,RCVD_IN_DNSWL_HI autolearn=ham version=3.3.1 Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.wl.linuxfoundation.org (Postfix) with ESMTP id 2D8C2202A5 for ; Wed, 10 Jul 2019 19:28:47 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728315AbfGJT2d (ORCPT ); Wed, 10 Jul 2019 15:28:33 -0400 Received: from mail-pf1-f195.google.com ([209.85.210.195]:33959 "EHLO mail-pf1-f195.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726111AbfGJT2b (ORCPT ); Wed, 10 Jul 2019 15:28:31 -0400 Received: by mail-pf1-f195.google.com with SMTP id b13so1556756pfo.1; Wed, 10 Jul 2019 12:28:31 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=sender:from:to:cc:subject:date:message-id:in-reply-to:references; bh=nZ7elc2UuS/FrboNoV7WD8dAaucbBsLM5Y4zkWcMIec=; b=qiCfx0rmc+8sLIBCZVBXWBshloWP9bWx9Q85U5m/78c5vqi7KwfuQl3wXQ0er2NMKq cnyPIzEt0dy+WgDXjj3vUzWKdUO2sbqFX9v0mbdvpak7wsrO6vFDYmVd+p2E2we+nF+X TsgaPawOW1GxWiMWLBAYHqDmxCcldeYpbrxA6oHbqFbPdCNZJw+pba5HkKPu8S+HRPKc 1A6MmMaxaZdwrbyD+h9GiZUBuUQXicaNbuOAKshkXytGyXN1SEcwnmimMnB8kQA/hp8E CLGJ+mDDsBmw1baxWsEFwCG/dZWfHAwpZBAVeCCAdolAc9ASpRguth3hJeqhVd0+Xq+y V2vw== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:sender:from:to:cc:subject:date:message-id :in-reply-to:references; bh=nZ7elc2UuS/FrboNoV7WD8dAaucbBsLM5Y4zkWcMIec=; b=RKRbkMYN/0/4XaINpfwrE9R3DnnFfq80C+Mlgw5C+ZNosUDZBrPDbiCBGyzik7aWns HKCCLmUnS5k5dSTH6ABVRbYfHl58vB1miwq8Y/WE6oXWH8rqzuMFDt2+jCuybVqhhRtk hW8+y5wb8uiDWlpSg+pO1c0Reo8HDC2O/Y75NeJX/ZilHH7EunDe6HzVZ6SStp8SRewC pjYgK9AmX5WzKBEYofm3amRiRL3jZPYJTeIlclpmotUgB3GmgwYr/mOE6OmiF812X+Vd kJHKkZbh0HGg7SFBFQOI+eXVO2TR0G4LQlWHAqYDjgq3oqZpPlbF9uaslpR+/hQTrVRa Bw4A== X-Gm-Message-State: APjAAAUwVMGNd4zdyNLV9naw0x66/81DQCR/EBFDGPTEsbjH/XkNTBn5 QidVAxxEvZqpRIRFS3AzkTw= X-Google-Smtp-Source: APXvYqznLwyb8aAh4JJt/ZHzUO2evjmORiPsPxcjE79kOScSuoqih3fkZmwydf/5r6XJjfnllDF69A== X-Received: by 2002:a63:18d:: with SMTP id 135mr38954916pgb.62.1562786910390; Wed, 10 Jul 2019 12:28:30 -0700 (PDT) Received: from localhost ([2620:10d:c091:500::3:2bbe]) by smtp.gmail.com with ESMTPSA id u137sm2963923pgc.91.2019.07.10.12.28.29 (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Wed, 10 Jul 2019 12:28:29 -0700 (PDT) From: Tejun Heo To: josef@toxicpanda.com, clm@fb.com, dsterba@suse.com Cc: axboe@kernel.dk, jack@suse.cz, linux-kernel@vger.kernel.org, linux-btrfs@vger.kernel.org, kernel-team@fb.com Subject: [PATCH 3/5] Btrfs: only associate the locked page with one async_cow struct Date: Wed, 10 Jul 2019 12:28:16 -0700 Message-Id: <20190710192818.1069475-4-tj@kernel.org> X-Mailer: git-send-email 2.17.1 In-Reply-To: <20190710192818.1069475-1-tj@kernel.org> References: <20190710192818.1069475-1-tj@kernel.org> Sender: linux-btrfs-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-btrfs@vger.kernel.org X-Virus-Scanned: ClamAV using ClamSMTP From: Chris Mason The btrfs writepages function collects a large range of pages flagged for delayed allocation, and then sends them down through the COW code for processing. When compression is on, we allocate one async_cow structure for every 512K, and then run those pages through the compression code for IO submission. writepages starts all of this off with a single page, locked by the original call to extent_write_cache_pages(), and it's important to keep track of this page because it has already been through clear_page_dirty_for_io(). The btrfs async_cow struct has a pointer to the locked_page, and when we're redirtying the page because compression had to fallback to uncompressed IO, we use page->index to decide if a given async_cow struct really owns that page. But, this is racey. If a given delalloc range is broken up into two async_cows (cow_A and cow_B), we can end up with something like this: compress_file_range(cowA) submit_compress_extents(cowA) submit compressed bios(cowA) put_page(locked_page) compress_file_range(cowB) ... The end result is that cowA is completed and cleaned up before cowB even starts processing. This means we can free locked_page() and reuse it elsewhere. If we get really lucky, it'll have the same page->index in its new home as it did before. While we're processing cowB, we might decide we need to fall back to uncompressed IO, and so compress_file_range() will call __set_page_dirty_nobufers() on cowB->locked_page. Without cgroups in use, this creates as a phantom dirty page, which isn't great but isn't the end of the world. With cgroups in use, we might crash in the accounting code because page->mapping->i_wb isn't set. [ 8308.523110] BUG: unable to handle kernel NULL pointer dereference at 00000000000000d0 [ 8308.531084] IP: percpu_counter_add_batch+0x11/0x70 [ 8308.538371] PGD 66534e067 P4D 66534e067 PUD 66534f067 PMD 0 [ 8308.541750] Oops: 0000 [#1] SMP DEBUG_PAGEALLOC [ 8308.551948] CPU: 16 PID: 2172 Comm: rm Not tainted [ 8308.566883] RIP: 0010:percpu_counter_add_batch+0x11/0x70 [ 8308.567891] RSP: 0018:ffffc9000a97bbe0 EFLAGS: 00010286 [ 8308.568986] RAX: 0000000000000005 RBX: 0000000000000090 RCX: 0000000000026115 [ 8308.570734] RDX: 0000000000000030 RSI: ffffffffffffffff RDI: 0000000000000090 [ 8308.572543] RBP: 0000000000000000 R08: fffffffffffffff5 R09: 0000000000000000 [ 8308.573856] R10: 00000000000260c0 R11: ffff881037fc26c0 R12: ffffffffffffffff [ 8308.580099] R13: ffff880fe4111548 R14: ffffc9000a97bc90 R15: 0000000000000001 [ 8308.582520] FS: 00007f5503ced480(0000) GS:ffff880ff7200000(0000) knlGS:0000000000000000 [ 8308.585440] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 [ 8308.587951] CR2: 00000000000000d0 CR3: 00000001e0459005 CR4: 0000000000360ee0 [ 8308.590707] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000 [ 8308.592865] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400 [ 8308.594469] Call Trace: [ 8308.595149] account_page_cleaned+0x15b/0x1f0 [ 8308.596340] __cancel_dirty_page+0x146/0x200 [ 8308.599395] truncate_cleanup_page+0x92/0xb0 [ 8308.600480] truncate_inode_pages_range+0x202/0x7d0 [ 8308.617392] btrfs_evict_inode+0x92/0x5a0 [ 8308.619108] evict+0xc1/0x190 [ 8308.620023] do_unlinkat+0x176/0x280 [ 8308.621202] do_syscall_64+0x63/0x1a0 [ 8308.623451] entry_SYSCALL_64_after_hwframe+0x42/0xb7 The fix here is to make asyc_cow->locked_page NULL everywhere but the one async_cow struct that's allowed to do things to the locked page. Signed-off-by: Chris Mason Fixes: 771ed689d2cd ("Btrfs: Optimize compressed writeback and reads") Reviewed-by: Josef Bacik --- fs/btrfs/extent_io.c | 2 +- fs/btrfs/inode.c | 25 +++++++++++++++++++++---- 2 files changed, 22 insertions(+), 5 deletions(-) diff --git a/fs/btrfs/extent_io.c b/fs/btrfs/extent_io.c index 5106008f5e28..a31574df06aa 100644 --- a/fs/btrfs/extent_io.c +++ b/fs/btrfs/extent_io.c @@ -1838,7 +1838,7 @@ static int __process_pages_contig(struct address_space *mapping, if (page_ops & PAGE_SET_PRIVATE2) SetPagePrivate2(pages[i]); - if (pages[i] == locked_page) { + if (locked_page && pages[i] == locked_page) { put_page(pages[i]); pages_locked++; continue; diff --git a/fs/btrfs/inode.c b/fs/btrfs/inode.c index 6e6df0eab324..a81e9860ee1f 100644 --- a/fs/btrfs/inode.c +++ b/fs/btrfs/inode.c @@ -666,10 +666,12 @@ static noinline void compress_file_range(struct async_chunk *async_chunk, * to our extent and set things up for the async work queue to run * cow_file_range to do the normal delalloc dance. */ - if (page_offset(async_chunk->locked_page) >= start && - page_offset(async_chunk->locked_page) <= end) + if (async_chunk->locked_page && + (page_offset(async_chunk->locked_page) >= start && + page_offset(async_chunk->locked_page)) <= end) { __set_page_dirty_nobuffers(async_chunk->locked_page); /* unlocked later on in the async handlers */ + } if (redirty) extent_range_redirty_for_io(inode, start, end); @@ -759,7 +761,7 @@ static noinline void submit_compressed_extents(struct async_chunk *async_chunk) async_extent->start + async_extent->ram_size - 1, WB_SYNC_ALL); - else if (ret) + else if (ret && async_chunk->locked_page) unlock_page(async_chunk->locked_page); kfree(async_extent); cond_resched(); @@ -1236,10 +1238,25 @@ static int cow_file_range_async(struct inode *inode, struct page *locked_page, async_chunk[i].inode = inode; async_chunk[i].start = start; async_chunk[i].end = cur_end; - async_chunk[i].locked_page = locked_page; async_chunk[i].write_flags = write_flags; INIT_LIST_HEAD(&async_chunk[i].extents); + /* + * The locked_page comes all the way from writepage and its + * the original page we were actually given. As we spread + * this large delalloc region across multiple async_cow + * structs, only the first struct needs a pointer to locked_page + * + * This way we don't need racey decisions about who is supposed + * to unlock it. + */ + if (locked_page) { + async_chunk[i].locked_page = locked_page; + locked_page = NULL; + } else { + async_chunk[i].locked_page = NULL; + } + btrfs_init_work(&async_chunk[i].work, btrfs_delalloc_helper, async_cow_start, async_cow_submit,