EXT4-fs error (device loop3): ext4_free_data:978: inode #18: block 37: comm syz.3.4051: IO error syncing itable block ================================================================== BUG: KCSAN: data-race in data_push_tail / vsnprintf write to 0xffffffff88ebe755 of 68 bytes by task 16810 on cpu 0: vsnprintf+0x2ce/0x860 lib/vsprintf.c:2898 vscnprintf+0x41/0x90 lib/vsprintf.c:3012 printk_sprint+0x30/0x2d0 kernel/printk/printk.c:2192 vprintk_store+0x599/0x860 kernel/printk/printk.c:2312 vprintk_emit+0x15a/0x610 kernel/printk/printk.c:2402 vprintk_default+0x26/0x30 kernel/printk/printk.c:2441 vprintk+0x1d/0x30 kernel/printk/printk_safe.c:82 _printk+0x79/0xa0 kernel/printk/printk.c:2451 batadv_tt_local_resize_to_mtu+0x17c/0x1c0 net/batman-adv/translation-table.c:3910 batadv_hard_if_event+0x1cd/0xe00 net/batman-adv/hard-interface.c:-1 notifier_call_chain kernel/notifier.c:85 [inline] raw_notifier_call_chain+0x6f/0x1b0 kernel/notifier.c:453 call_netdevice_notifiers_info net/core/dev.c:2230 [inline] call_netdevice_notifiers_mtu+0xb6/0x110 net/core/dev.c:2305 netif_set_mtu_ext+0x391/0x480 net/core/dev.c:9871 netif_set_mtu+0x4a/0xf0 net/core/dev.c:9892 dev_set_mtu+0xc1/0x170 net/core/dev_api.c:248 dev_ifsioc+0x474/0xaa0 net/core/dev_ioctl.c:590 dev_ioctl+0x70a/0x960 net/core/dev_ioctl.c:842 sock_do_ioctl+0x197/0x220 net/socket.c:1268 sock_ioctl+0x41b/0x610 net/socket.c:1375 vfs_ioctl fs/ioctl.c:51 [inline] __do_sys_ioctl fs/ioctl.c:597 [inline] __se_sys_ioctl+0xce/0x140 fs/ioctl.c:583 __x64_sys_ioctl+0x43/0x50 fs/ioctl.c:583 x64_sys_call+0x14b0/0x3000 arch/x86/include/generated/asm/syscalls_64.h:17 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline] do_syscall_64+0xd8/0x2a0 arch/x86/entry/syscall_64.c:94 entry_SYSCALL_64_after_hwframe+0x77/0x7f read to 0xffffffff88ebe778 of 8 bytes by task 16797 on cpu 1: data_make_reusable kernel/printk/printk_ringbuffer.c:608 [inline] data_push_tail+0x100/0x470 kernel/printk/printk_ringbuffer.c:693 data_alloc+0x11b/0x390 kernel/printk/printk_ringbuffer.c:1089 prb_reserve+0x964/0xb60 kernel/printk/printk_ringbuffer.c:1724 vprintk_store+0x56d/0x860 kernel/printk/printk.c:2302 vprintk_emit+0x15a/0x610 kernel/printk/printk.c:2402 vprintk_default+0x26/0x30 kernel/printk/printk.c:2441 vprintk+0x1d/0x30 kernel/printk/printk_safe.c:82 _printk+0x79/0xa0 kernel/printk/printk.c:2451 __ext4_error_inode+0x30f/0x3f0 fs/ext4/super.c:848 __ext4_handle_dirty_metadata+0x26c/0x470 fs/ext4/ext4_jbd2.c:399 ext4_free_data+0x251/0x2a0 fs/ext4/indirect.c:978 ext4_free_branches+0x62/0x410 fs/ext4/indirect.c:1108 ext4_ind_truncate+0x503/0x830 fs/ext4/indirect.c:1181 ext4_truncate+0x6de/0xae0 fs/ext4/inode.c:4614 ext4_truncate_failed_write fs/ext4/truncate.h:22 [inline] ext4_write_end+0x549/0x730 fs/ext4/inode.c:1491 generic_perform_write+0x312/0x490 mm/filemap.c:4335 ext4_buffered_write_iter+0x1ee/0x3c0 fs/ext4/file.c:299 ext4_file_write_iter+0x387/0xf60 fs/ext4/file.c:-1 new_sync_write fs/read_write.c:593 [inline] vfs_write+0x52a/0x960 fs/read_write.c:686 ksys_write+0xda/0x1a0 fs/read_write.c:738 __do_sys_write fs/read_write.c:749 [inline] __se_sys_write fs/read_write.c:746 [inline] __x64_sys_write+0x40/0x50 fs/read_write.c:746 x64_sys_call+0x2847/0x3000 arch/x86/include/generated/asm/syscalls_64.h:2 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline] do_syscall_64+0xd8/0x2a0 arch/x86/entry/syscall_64.c:94 entry_SYSCALL_64_after_hwframe+0x77/0x7f value changed: 0x00000001000007e9 -> 0x77656e2074696620 Reported by Kernel Concurrency Sanitizer on: CPU: 1 UID: 0 PID: 16797 Comm: syz.3.4051 Not tainted syzkaller #0 PREEMPT(voluntary) Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/25/2025 ================================================================== Buffer I/O error on dev loop3, logical block 1, lost sync page write EXT4-fs (loop3): I/O error while writing superblock EXT4-fs error (device loop3): ext4_check_bdev_write_error:227: comm syz.3.4051: Error while async write back metadata Buffer I/O error on dev loop3, logical block 1, lost sync page write EXT4-fs (loop3): I/O error while writing superblock EXT4-fs error (device loop3): ext4_check_bdev_write_error:227: comm syz.3.4051: Error while async write back metadata Buffer I/O error on dev loop3, logical block 1, lost sync page write EXT4-fs (loop3): I/O error while writing superblock EXT4-fs error (device loop3): ext4_check_bdev_write_error:227: comm syz.3.4051: Error while async write back metadata Buffer I/O error on dev loop3, logical block 1, lost sync page write EXT4-fs (loop3): I/O error while writing superblock EXT4-fs error (device loop3): ext4_check_bdev_write_error:227: comm syz.3.4051: Error while async write back metadata Buffer I/O error on dev loop3, logical block 1, lost sync page write EXT4-fs (loop3): I/O error while writing superblock EXT4-fs error (device loop3): ext4_check_bdev_write_error:227: comm syz.3.4051: Error while async write back metadata Buffer I/O error on dev loop3, logical block 1, lost sync page write EXT4-fs (loop3): I/O error while writing superblock EXT4-fs error (device loop3): ext4_check_bdev_write_error:227: comm syz.3.4051: Error while async write back metadata Buffer I/O error on dev loop3, logical block 1, lost sync page write EXT4-fs (loop3): I/O error while writing superblock Buffer I/O error on dev loop3, logical block 37, lost sync page write EXT4-fs error (device loop3): ext4_splice_branch:472: inode #18: block 37: comm syz.3.4051: IO error syncing itable block Buffer I/O error on dev loop3, logical block 1, lost sync page write EXT4-fs (loop3): I/O error while writing superblock EXT4-fs error (device loop3): ext4_check_bdev_write_error:227: comm syz.3.4051: Error while async write back metadata EXT4-fs (loop3): I/O error while writing superblock EXT4-fs error (device loop3): ext4_check_bdev_write_error:227: comm syz.3.4051: Error while async write back metadata EXT4-fs warning (device loop3): ext4_end_bio:372: I/O error 10 writing to inode 18 starting block 41) Buffer I/O error on device loop3, logical block 41 Buffer I/O error on device loop3, logical block 42 Buffer I/O error on device loop3, logical block 43 Buffer I/O error on device loop3, logical block 44 EXT4-fs warning (device loop3): ext4_end_bio:372: I/O error 10 writing to inode 18 starting block 49) Buffer I/O error on device loop3, logical block 49 Buffer I/O error on device loop3, logical block 50 Buffer I/O error on device loop3, logical block 51 Buffer I/O error on device loop3, logical block 52 EXT4-fs warning (device loop3): ext4_end_bio:372: I/O error 10 writing to inode 18 starting block 57) Buffer I/O error on device loop3, logical block 57 Buffer I/O error on device loop3, logical block 58 EXT4-fs warning (device loop3): ext4_end_bio:372: I/O error 10 writing to inode 18 starting block 65) EXT4-fs warning (device loop3): ext4_end_bio:372: I/O error 10 writing to inode 18 starting block 45) EXT4-fs warning (device loop3): ext4_end_bio:372: I/O error 10 writing to inode 18 starting block 53) EXT4-fs warning (device loop3): ext4_end_bio:372: I/O error 10 writing to inode 18 starting block 61) EXT4-fs warning (device loop3): ext4_end_bio:372: I/O error 10 writing to inode 18 starting block 125) EXT4-fs warning (device loop3): ext4_end_bio:372: I/O error 10 writing to inode 18 starting block 161) EXT4-fs warning (device loop3): ext4_end_bio:372: I/O error 10 writing to inode 18 starting block 201)