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BUG: KCSAN: data-race in __mark_inode_dirty / __writeback_single_inode

write to 0xffff8881252446f8 of 8 bytes by task 674 on cpu 0:
 __writeback_single_inode+0x328/0x8e0 fs/fs-writeback.c:1486
 writeback_sb_inodes+0x4ba/0xa50 fs/fs-writeback.c:1716
 __writeback_inodes_wb+0xe8/0x1b0 fs/fs-writeback.c:1785
 wb_writeback+0x557/0x6a0 fs/fs-writeback.c:1894
 wb_check_start_all fs/fs-writeback.c:2018 [inline]
 wb_do_writeback fs/fs-writeback.c:2044 [inline]
 wb_workfn+0x758/0x9b0 fs/fs-writeback.c:2078
 process_one_work+0x413/0x8f0 kernel/workqueue.c:2264
 worker_thread+0xa0/0x800 kernel/workqueue.c:2410
 kthread+0x1d4/0x200 drivers/block/aoe/aoecmd.c:1253
 ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:352

read to 0xffff8881252446f8 of 8 bytes by task 12116 on cpu 1:
 __mark_inode_dirty+0xb8/0x940 fs/fs-writeback.c:2272
 mark_buffer_dirty+0x29c/0x2c0 fs/buffer.c:1156
 __block_commit_write.isra.0+0x11f/0x170 fs/buffer.c:2081
 block_commit_write fs/buffer.c:2473 [inline]
 block_page_mkwrite+0x226/0x230 fs/buffer.c:2522
 ext4_page_mkwrite+0x50e/0x850 fs/ext4/inode.c:5933
 do_page_mkwrite+0x100/0x210 mm/memory.c:2364
 wp_page_shared mm/memory.c:2691 [inline]
 do_wp_page+0xae5/0xd20 mm/memory.c:2803
 handle_pte_fault mm/memory.c:4049 [inline]
 __handle_mm_fault+0x1d16/0x2e00 mm/memory.c:4163
 handle_mm_fault+0x21b/0x530 mm/memory.c:4200
 do_user_addr_fault arch/x86/mm/fault.c:1442 [inline]
 do_page_fault+0x496/0xa3d arch/x86/mm/fault.c:1517
 page_fault+0x34/0x40 arch/x86/entry/entry_64.S:1203

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 PID: 12116 Comm: syz-executor.1 Not tainted 5.6.0-rc1-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
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