loop3: detected capacity change from 0 to 128
==================================================================
BUG: KCSAN: data-race in __mark_inode_dirty / writeback_single_inode

write to 0xffff88811a028128 of 4 bytes by task 9254 on cpu 0:
 writeback_single_inode+0x150/0x3f0 fs/fs-writeback.c:1837
 sync_inode_metadata+0x5b/0x90 fs/fs-writeback.c:2923
 __generic_file_fsync+0xf8/0x140 fs/libfs.c:1550
 fat_file_fsync+0x49/0x100 fs/fat/file.c:191
 vfs_fsync_range+0x10d/0x130 fs/sync.c:187
 generic_write_sync include/linux/fs.h:3046 [inline]
 generic_file_write_iter+0x1b8/0x2f0 mm/filemap.c:4389
 iter_file_splice_write+0x666/0xa60 fs/splice.c:738
 do_splice_from fs/splice.c:938 [inline]
 direct_splice_actor+0x156/0x2a0 fs/splice.c:1161
 splice_direct_to_actor+0x312/0x680 fs/splice.c:1105
 do_splice_direct_actor fs/splice.c:1204 [inline]
 do_splice_direct+0xda/0x150 fs/splice.c:1230
 do_sendfile+0x380/0x650 fs/read_write.c:1370
 __do_sys_sendfile64 fs/read_write.c:1431 [inline]
 __se_sys_sendfile64 fs/read_write.c:1417 [inline]
 __x64_sys_sendfile64+0x105/0x150 fs/read_write.c:1417
 x64_sys_call+0x2bb4/0x3000 arch/x86/include/generated/asm/syscalls_64.h:41
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0xd2/0x200 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

read to 0xffff88811a028128 of 4 bytes by task 9248 on cpu 1:
 __mark_inode_dirty+0x191/0x750 fs/fs-writeback.c:2588
 fat_update_time+0x1ec/0x200 fs/fat/misc.c:357
 inode_update_time fs/inode.c:2117 [inline]
 touch_atime+0x148/0x340 fs/inode.c:2190
 file_accessed include/linux/fs.h:2673 [inline]
 filemap_splice_read+0x6ba/0x740 mm/filemap.c:3083
 do_splice_read fs/splice.c:982 [inline]
 splice_direct_to_actor+0x26f/0x680 fs/splice.c:1086
 do_splice_direct_actor fs/splice.c:1204 [inline]
 do_splice_direct+0xda/0x150 fs/splice.c:1230
 do_sendfile+0x380/0x650 fs/read_write.c:1370
 __do_sys_sendfile64 fs/read_write.c:1431 [inline]
 __se_sys_sendfile64 fs/read_write.c:1417 [inline]
 __x64_sys_sendfile64+0x105/0x150 fs/read_write.c:1417
 x64_sys_call+0x2bb4/0x3000 arch/x86/include/generated/asm/syscalls_64.h:41
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0xd2/0x200 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

value changed: 0x00000070 -> 0x00000002

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 UID: 0 PID: 9248 Comm: syz.3.949 Not tainted syzkaller #0 PREEMPT(voluntary) 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 08/18/2025
==================================================================
syz.3.949: attempt to access beyond end of device
loop3: rw=2049, sector=128, nr_sectors = 1 limit=128
Buffer I/O error on dev loop3, logical block 128, lost async page write