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Mon, 18 Sep 2023 06:48:22 +0200 (CEST) Received: from defiant.home (78-1-184-14.adsl.net.t-com.hr [78.1.184.14]) by domac.alu.hr (Postfix) with ESMTPSA id 029B760155; Mon, 18 Sep 2023 06:48:20 +0200 (CEST) DKIM-Signature: v=1; a=rsa-sha256; c=simple/simple; d=alu.unizg.hr; s=mail; t=1695012502; bh=znt8nZ/ul1DmeyQFC/6Gimy2V/JLtuGQw9NojRoWjhM=; h=From:To:Cc:Subject:Date:From; b=FZk3FbxDDyQbvmrSCZRMvbwOIiHtsacRA1ZAmdLvn4W0L5VfM8ODMvmuc9Vnn0v42 AG+oqQoV+EEwwiQL0idcpbEIfePzUeSNbEiGk3B/f0qHAiFhrp7ekbYDUxJiSS2spF jEVgS0UKyoVr87F3zPIaPC3aPfMcsUtD+ZATid3PPwYdd4MboFRo7KcjNtgx3tzgKp rUtMViry8fwShzWIVjUlvnZjZLFdHqp5FR6omnjP8ORi3nG1JzmZBH661JjY2j0yvR q9gl6JOo8X2KYQRXc3unAnkTtiveRQS9PhoMHY/z9jbCKmTZYybnKjI19pdvkAg9TU B935noV77jB5w== From: Mirsad Goran Todorovac To: Philipp Stanner , linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org Cc: Matthew Wilcox , Mirsad Goran Todorovac , Jan Kara , Chris Mason , Andrew Morton , Josef Bacik , David Sterba , linux-btrfs@vger.kernel.org, linux-mm@kvack.org Subject: [PATCH v1 1/1] xarray: fix the data-race in xas_find_chunk() by using READ_ONCE() Date: Mon, 18 Sep 2023 06:47:40 +0200 Message-Id: <20230918044739.29782-1-mirsad.todorovac@alu.unizg.hr> X-Mailer: git-send-email 2.34.1 MIME-Version: 1.0 X-Spam-Status: No, score=-0.6 required=5.0 tests=DKIM_INVALID,DKIM_SIGNED, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE, SPF_PASS autolearn=unavailable autolearn_force=no version=3.4.6 X-Spam-Checker-Version: SpamAssassin 3.4.6 (2021-04-09) on pete.vger.email Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org X-Greylist: Sender passed SPF test, not delayed by milter-greylist-4.6.4 (pete.vger.email [0.0.0.0]); Sun, 17 Sep 2023 21:49:38 -0700 (PDT) X-getmail-retrieved-from-mailbox: INBOX X-GMAIL-THRID: 1777349512381039764 X-GMAIL-MSGID: 1777349512381039764 KCSAN has discovered the following data-race: [ 206.510010] ================================================================== [ 206.510035] BUG: KCSAN: data-race in xas_clear_mark / xas_find_marked [ 206.510067] write to 0xffff963df6a90fe0 of 8 bytes by interrupt on cpu 22: [ 206.510081] xas_clear_mark (./arch/x86/include/asm/bitops.h:178 ./include/asm-generic/bitops/instrumented-non-atomic.h:115 lib/xarray.c:102 lib/xarray.c:914) [ 206.510097] __xa_clear_mark (lib/xarray.c:1923) [ 206.510114] __folio_end_writeback (mm/page-writeback.c:2981) [ 206.510128] folio_end_writeback (mm/filemap.c:1616) [ 206.510143] end_page_writeback (mm/folio-compat.c:28) [ 206.510155] btrfs_page_clear_writeback (fs/btrfs/subpage.c:646) btrfs [ 206.510994] end_bio_extent_writepage (./include/linux/bio.h:84 fs/btrfs/extent_io.c:542) btrfs [ 206.511817] __btrfs_bio_end_io (fs/btrfs/bio.c:117 fs/btrfs/bio.c:112) btrfs [ 206.512640] btrfs_orig_bbio_end_io (fs/btrfs/bio.c:164) btrfs [ 206.513497] btrfs_simple_end_io (fs/btrfs/bio.c:380) btrfs [ 206.514350] bio_endio (block/bio.c:1617) [ 206.514362] blk_mq_end_request_batch (block/blk-mq.c:837 block/blk-mq.c:1073) [ 206.514377] nvme_pci_complete_batch (drivers/nvme/host/pci.c:986) nvme [ 206.514437] nvme_irq (drivers/nvme/host/pci.c:1086) nvme [ 206.514500] __handle_irq_event_percpu (kernel/irq/handle.c:158) [ 206.514517] handle_irq_event (kernel/irq/handle.c:195 kernel/irq/handle.c:210) [ 206.514533] handle_edge_irq (kernel/irq/chip.c:836) [ 206.514549] __common_interrupt (./include/linux/irqdesc.h:161 arch/x86/kernel/irq.c:238 arch/x86/kernel/irq.c:257) [ 206.514563] common_interrupt (arch/x86/kernel/irq.c:247 (discriminator 14)) [ 206.514583] asm_common_interrupt (./arch/x86/include/asm/idtentry.h:636) [ 206.514599] kcsan_setup_watchpoint (kernel/kcsan/core.c:705 (discriminator 1)) [ 206.514612] __tsan_read8 (kernel/kcsan/core.c:1025) [ 206.514626] steal_from_bitmap.part.0 (./include/linux/find.h:186 fs/btrfs/free-space-cache.c:2557 fs/btrfs/free-space-cache.c:2613) btrfs [ 206.515491] __btrfs_add_free_space (fs/btrfs/free-space-cache.c:2689 fs/btrfs/free-space-cache.c:2667) btrfs [ 206.516361] btrfs_add_free_space_async_trimmed (fs/btrfs/free-space-cache.c:2798) btrfs [ 206.517231] add_new_free_space (fs/btrfs/block-group.c:550) btrfs [ 206.518095] load_free_space_tree (fs/btrfs/free-space-tree.c:1595 fs/btrfs/free-space-tree.c:1658) btrfs [ 206.518953] caching_thread (fs/btrfs/block-group.c:873) btrfs [ 206.519800] btrfs_work_helper (fs/btrfs/async-thread.c:314) btrfs [ 206.520643] process_one_work (kernel/workqueue.c:2600) [ 206.520658] worker_thread (./include/linux/list.h:292 kernel/workqueue.c:2752) [ 206.520672] kthread (kernel/kthread.c:389) [ 206.520684] ret_from_fork (arch/x86/kernel/process.c:145) [ 206.520701] ret_from_fork_asm (arch/x86/entry/entry_64.S:312) [ 206.520722] read to 0xffff963df6a90fe0 of 8 bytes by task 2793 on cpu 6: [ 206.520735] xas_find_marked (./include/linux/xarray.h:1706 lib/xarray.c:1354) [ 206.520750] filemap_get_folios_tag (mm/filemap.c:1975 mm/filemap.c:2273) [ 206.520763] __filemap_fdatawait_range (mm/filemap.c:519) [ 206.520777] filemap_fdatawait_range (mm/filemap.c:556) [ 206.520790] btrfs_wait_ordered_range (fs/btrfs/ordered-data.c:839) btrfs [ 206.521641] btrfs_sync_file (fs/btrfs/file.c:1859) btrfs [ 206.522495] vfs_fsync_range (fs/sync.c:188) [ 206.522509] __x64_sys_fsync (./include/linux/file.h:45 fs/sync.c:213 fs/sync.c:220 fs/sync.c:218 fs/sync.c:218) [ 206.522522] do_syscall_64 (arch/x86/entry/common.c:50 arch/x86/entry/common.c:80) [ 206.522535] entry_SYSCALL_64_after_hwframe (arch/x86/entry/entry_64.S:120) [ 206.522557] value changed: 0xfffffffffff80000 -> 0xfffffffffff00000 [ 206.522574] Reported by Kernel Concurrency Sanitizer on: [ 206.522585] CPU: 6 PID: 2793 Comm: tracker-extract Tainted: G L 6.5.0-rc6+ #44 [ 206.522600] Hardware name: ASRock X670E PG Lightning/X670E PG Lightning, BIOS 1.21 04/26/2023 [ 206.522608] ================================================================== As Jan Kara explained, the problem is in the function xas_find_chuck(): /* Private */ static inline unsigned int xas_find_chunk(struct xa_state *xas, bool advance, xa_mark_t mark) { unsigned long *addr = xas->xa_node->marks[(__force unsigned)mark]; unsigned int offset = xas->xa_offset; if (advance) offset++; if (XA_CHUNK_SIZE == BITS_PER_LONG) { if (offset < XA_CHUNK_SIZE) { → unsigned long data = *addr & (~0UL << offset); if (data) return __ffs(data); } return XA_CHUNK_SIZE; } return find_next_bit(addr, XA_CHUNK_SIZE, offset); } In particular, the line unsigned long data = *addr & (~0UL << offset); contains a data race that is best avoided using READ_ONCE(), which eliminated the KCSAN data-race warning completely. Reported-by: Mirsad Goran Todorovac Suggested-by: Jan Kara Fixes: b803b42823d0d ("xarray: Add XArray iterators") Matthew Wilcox Cc: Chris Mason Cc: Andrew Morton Cc: Josef Bacik Cc: David Sterba Cc: linux-btrfs@vger.kernel.org Cc: linux-fsdevel@vger.kernel.org Cc: linux-mm@kvack.org Signed-off-by: Mirsad Goran Todorovac --- v1: the proposed fix (RFC) include/linux/xarray.h | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/include/linux/xarray.h b/include/linux/xarray.h index cb571dfcf4b1..1715fd322d62 100644 --- a/include/linux/xarray.h +++ b/include/linux/xarray.h @@ -1720,7 +1720,7 @@ static inline unsigned int xas_find_chunk(struct xa_state *xas, bool advance, offset++; if (XA_CHUNK_SIZE == BITS_PER_LONG) { if (offset < XA_CHUNK_SIZE) { - unsigned long data = *addr & (~0UL << offset); + unsigned long data = READ_ONCE(*addr) & (~0UL << offset); if (data) return __ffs(data); }