syzbot

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BUG: KCSAN: data-race in generic_buffers_fsync_noflush / writeback_single_inode

write to 0xffff88810049a008 of 4 bytes by task 4075 on cpu 1:
 writeback_single_inode+0x14a/0x3e0 fs/fs-writeback.c:1798
 sync_inode_metadata+0x5b/0x90 fs/fs-writeback.c:2884
 generic_buffers_fsync_noflush+0xd9/0x120 fs/buffer.c:619
 ext4_fsync_nojournal fs/ext4/fsync.c:88 [inline]
 ext4_sync_file+0x1ab/0x690 fs/ext4/fsync.c:147
 vfs_fsync_range+0x10d/0x130 fs/sync.c:187
 generic_write_sync include/linux/fs.h:3042 [inline]
 ext4_buffered_write_iter+0x34f/0x3c0 fs/ext4/file.c:305
 ext4_file_write_iter+0x383/0xf00 fs/ext4/file.c:-1
 iter_file_splice_write+0x663/0xa60 fs/splice.c:738
 do_splice_from fs/splice.c:938 [inline]
 direct_splice_actor+0x153/0x2a0 fs/splice.c:1161
 splice_direct_to_actor+0x30f/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+0x2bb0/0x2ff0 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 0xffff88810049a008 of 4 bytes by task 4078 on cpu 0:
 generic_buffers_fsync_noflush+0x80/0x120 fs/buffer.c:614
 ext4_fsync_nojournal fs/ext4/fsync.c:88 [inline]
 ext4_sync_file+0x1ab/0x690 fs/ext4/fsync.c:147
 vfs_fsync_range+0x10d/0x130 fs/sync.c:187
 generic_write_sync include/linux/fs.h:3042 [inline]
 ext4_buffered_write_iter+0x34f/0x3c0 fs/ext4/file.c:305
 ext4_file_write_iter+0x383/0xf00 fs/ext4/file.c:-1
 iter_file_splice_write+0x663/0xa60 fs/splice.c:738
 do_splice_from fs/splice.c:938 [inline]
 direct_splice_actor+0x153/0x2a0 fs/splice.c:1161
 splice_direct_to_actor+0x30f/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+0x2bb0/0x2ff0 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: 0x00000038 -> 0x00000002

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 UID: 0 PID: 4078 Comm: syz.0.178 Not tainted syzkaller #0 PREEMPT(voluntary) 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 07/12/2025
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