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BUG: KCSAN: data-race in __writeback_single_inode / xas_set_mark

write to 0xffff8881049fb674 of 4 bytes by task 8004 on cpu 0:
 xa_mark_set lib/xarray.c:71 [inline]
 xas_set_mark+0x12b/0x140 lib/xarray.c:900
 __folio_start_writeback+0x16b/0x370 mm/page-writeback.c:3011
 __block_write_full_folio+0x526/0x8d0 fs/buffer.c:1812
 block_write_full_folio+0x2c1/0x2e0 fs/buffer.c:-1
 mpage_write_folio fs/mpage.c:640 [inline]
 __mpage_writepages+0x722/0x1370 fs/mpage.c:686
 mpage_writepages include/linux/mpage.h:27 [inline]
 fat_writepages+0x26/0x30 fs/fat/inode.c:200
 do_writepages+0x1b9/0x300 mm/page-writeback.c:2560
 filemap_writeback mm/filemap.c:387 [inline]
 filemap_fdatawrite_range mm/filemap.c:412 [inline]
 file_write_and_wait_range+0x178/0x2f0 mm/filemap.c:786
 simple_fsync_noflush+0x42/0x120 fs/libfs.c:1558
 fat_file_fsync+0x7e/0x100 fs/fat/file.c:193
 vfs_fsync_range+0xc5/0xe0 fs/sync.c:186
 generic_write_sync include/linux/fs.h:2686 [inline]
 generic_file_write_iter+0x1a3/0x1f0 mm/filemap.c:4521
 iter_file_splice_write+0x6a0/0xa60 fs/splice.c:736
 do_splice_from fs/splice.c:936 [inline]
 direct_splice_actor+0x158/0x280 fs/splice.c:1159
 splice_direct_to_actor+0x2f9/0x680 fs/splice.c:1103
 do_splice_direct_actor fs/splice.c:1202 [inline]
 do_splice_direct+0x119/0x1a0 fs/splice.c:1228
 do_sendfile+0x37d/0x640 fs/read_write.c:1371
 __do_sys_sendfile64 fs/read_write.c:1432 [inline]
 __se_sys_sendfile64 fs/read_write.c:1418 [inline]
 __x64_sys_sendfile64+0x105/0x150 fs/read_write.c:1418
 x64_sys_call+0x1015/0x2550 arch/x86/include/generated/asm/syscalls_64.h:41
 do_syscall_x64 arch/x86/entry/syscall_64.c:61 [inline]
 do_syscall_64+0x112/0x360 arch/x86/entry/syscall_64.c:84
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

read to 0xffff8881049fb674 of 4 bytes by task 8059 on cpu 1:
 xa_marked include/linux/xarray.h:424 [inline]
 mapping_tagged include/linux/fs.h:502 [inline]
 __writeback_single_inode+0x208/0x790 fs/fs-writeback.c:1837
 writeback_single_inode+0x16d/0x410 fs/fs-writeback.c:1926
 sync_inode_metadata+0x6e/0xa0 fs/fs-writeback.c:3100
 simple_fsync_noflush+0xdb/0x120 fs/libfs.c:1570
 fat_file_fsync+0x7e/0x100 fs/fat/file.c:193
 vfs_fsync_range+0xc5/0xe0 fs/sync.c:186
 generic_write_sync include/linux/fs.h:2686 [inline]
 generic_file_write_iter+0x1a3/0x1f0 mm/filemap.c:4521
 iter_file_splice_write+0x6a0/0xa60 fs/splice.c:736
 do_splice_from fs/splice.c:936 [inline]
 direct_splice_actor+0x158/0x280 fs/splice.c:1159
 splice_direct_to_actor+0x2f9/0x680 fs/splice.c:1103
 do_splice_direct_actor fs/splice.c:1202 [inline]
 do_splice_direct+0x119/0x1a0 fs/splice.c:1228
 do_sendfile+0x37d/0x640 fs/read_write.c:1371
 __do_sys_sendfile64 fs/read_write.c:1432 [inline]
 __se_sys_sendfile64 fs/read_write.c:1418 [inline]
 __x64_sys_sendfile64+0x105/0x150 fs/read_write.c:1418
 x64_sys_call+0x1015/0x2550 arch/x86/include/generated/asm/syscalls_64.h:41
 do_syscall_x64 arch/x86/entry/syscall_64.c:61 [inline]
 do_syscall_64+0x112/0x360 arch/x86/entry/syscall_64.c:84
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

value changed: 0x05000021 -> 0x00000021

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 UID: 0 PID: 8059 Comm: syz.2.5520 Not tainted syzkaller #0 PREEMPT(lazy) 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 07/24/2026
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