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BUG: KCSAN: data-race in __xa_set_mark / find_get_pages_range_tag

write to 0xffff88811e64d6a8 of 8 bytes by task 14604 on cpu 1:
 instrument_write include/linux/instrumented.h:42 [inline]
 __test_and_set_bit include/asm-generic/bitops/instrumented-non-atomic.h:71 [inline]
 node_set_mark lib/xarray.c:93 [inline]
 xas_set_mark lib/xarray.c:879 [inline]
 __xa_set_mark+0x233/0x330 lib/xarray.c:1708
 __set_page_dirty+0x17e/0x1d0 fs/buffer.c:609
 mark_buffer_dirty+0x12e/0x260 fs/buffer.c:1137
 __block_commit_write fs/buffer.c:2084 [inline]
 block_write_end+0x13d/0x220 fs/buffer.c:2162
 generic_write_end+0x5c/0x250 fs/buffer.c:2176
 fat_write_end+0x4a/0x160 fs/fat/inode.c:249
 pagecache_write_end+0x54/0x70 mm/filemap.c:3331
 cont_expand_zero fs/buffer.c:2401 [inline]
 cont_write_begin+0x23f/0x610 fs/buffer.c:2459
 fat_write_begin+0x61/0xf0 fs/fat/inode.c:235
 pagecache_write_begin+0x54/0x70 mm/filemap.c:3320
 generic_cont_expand_simple+0x6d/0x100 fs/buffer.c:2360
 fat_cont_expand+0x3a/0x160 fs/fat/file.c:222
 fat_setattr+0x229/0x760 fs/fat/file.c:501
 notify_change+0x7d7/0xa80 fs/attr.c:336
 do_truncate fs/open.c:64 [inline]
 do_sys_ftruncate+0x39f/0x3e0 fs/open.c:195
 __do_sys_ftruncate fs/open.c:205 [inline]
 __se_sys_ftruncate fs/open.c:203 [inline]
 __x64_sys_ftruncate+0x2f/0x40 fs/open.c:203
 do_syscall_64+0x39/0x80 arch/x86/entry/common.c:46
 entry_SYSCALL_64_after_hwframe+0x44/0xa9

read to 0xffff88811e64d6a8 of 8 bytes by task 14616 on cpu 0:
 xas_find_chunk include/linux/xarray.h:1625 [inline]
 xas_next_marked include/linux/xarray.h:1656 [inline]
 find_get_pages_range_tag+0x30c/0x5b0 mm/filemap.c:2074
 pagevec_lookup_range_tag+0x37/0x50 mm/swap.c:1122
 write_cache_pages+0x1f8/0x840 mm/page-writeback.c:2203
 mpage_writepages+0x6d/0x120 fs/mpage.c:714
 fat_writepages+0x20/0x30 fs/fat/inode.c:205
 do_writepages+0x7b/0x150 mm/page-writeback.c:2352
 __filemap_fdatawrite_range+0x19b/0x1d0 mm/filemap.c:422
 sync_file_range+0x1a5/0x210 fs/sync.c:304
 ksys_sync_file_range fs/sync.c:376 [inline]
 __do_sys_sync_file_range fs/sync.c:385 [inline]
 __se_sys_sync_file_range fs/sync.c:382 [inline]
 __x64_sys_sync_file_range+0x7c/0xd0 fs/sync.c:382
 do_syscall_64+0x39/0x80 arch/x86/entry/common.c:46
 entry_SYSCALL_64_after_hwframe+0x44/0xa9

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 PID: 14616 Comm: syz-executor.5 Not tainted 5.9.0-rc5-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
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