syzbot

FAT-fs (loop0): error, corrupted file size (i_pos 548, 522)
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BUG: KCSAN: data-race in data_alloc / data_push_tail

write to 0xffffffff890fe9a8 of 8 bytes by interrupt on cpu 1:
 data_alloc+0x259/0x390 kernel/printk/printk_ringbuffer.c:1116
 prb_reserve+0x8d7/0xae0 kernel/printk/printk_ringbuffer.c:1724
 vprintk_store+0x54a/0x910 kernel/printk/printk.c:2302
 vprintk_emit+0x1a4/0x600 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
 lapbeth_xmit+0x1bd/0x1c0 drivers/net/wan/lapbether.c:-1
 __netdev_start_xmit include/linux/netdevice.h:5273 [inline]
 netdev_start_xmit include/linux/netdevice.h:5282 [inline]
 xmit_one net/core/dev.c:3866 [inline]
 dev_hard_start_xmit+0x125/0x3e0 net/core/dev.c:3882
 __dev_queue_xmit+0xdb1/0x1f20 net/core/dev.c:4832
 dev_queue_xmit include/linux/netdevice.h:3381 [inline]
 x25_send_frame+0xfe/0x130 net/x25/x25_dev.c:193
 x25_transmit_restart_confirmation net/x25/x25_link.c:178 [inline]
 x25_link_control+0x3d1/0x500 net/x25/x25_link.c:-1
 x25_receive_data net/x25/x25_dev.c:43 [inline]
 x25_lapb_receive_frame+0x2e0/0x750 net/x25/x25_dev.c:127
 __netif_receive_skb_one_core net/core/dev.c:6152 [inline]
 netif_receive_skb_core+0x122/0x130 net/core/dev.c:6177
 lapbeth_napi_poll+0x42/0x90 drivers/net/wan/lapbether.c:100
 __napi_poll+0x5f/0x300 net/core/dev.c:7681
 napi_poll net/core/dev.c:7744 [inline]
 net_rx_action+0x452/0x930 net/core/dev.c:7896
 handle_softirqs+0xb9/0x280 kernel/softirq.c:622
 do_softirq+0x45/0x60 kernel/softirq.c:523
 __local_bh_enable_ip+0x70/0x80 kernel/softirq.c:450
 __raw_spin_unlock_bh include/linux/spinlock_api_smp.h:167 [inline]
 _raw_spin_unlock_bh+0x36/0x40 kernel/locking/spinlock.c:210
 spin_unlock_bh include/linux/spinlock.h:396 [inline]
 nsim_dev_trap_report drivers/net/netdevsim/dev.c:890 [inline]
 nsim_dev_trap_report_work+0x52b/0x630 drivers/net/netdevsim/dev.c:921
 process_one_work kernel/workqueue.c:3257 [inline]
 process_scheduled_works+0x4cd/0x9d0 kernel/workqueue.c:3340
 worker_thread+0x581/0x770 kernel/workqueue.c:3421
 kthread+0x488/0x510 kernel/kthread.c:463
 ret_from_fork+0x148/0x280 arch/x86/kernel/process.c:158
 ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:246

read to 0xffffffff890fe9a8 of 8 bytes by task 25888 on cpu 0:
 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+0x8d7/0xae0 kernel/printk/printk_ringbuffer.c:1724
 vprintk_store+0x54a/0x910 kernel/printk/printk.c:2302
 vprintk_emit+0x1a4/0x600 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
 _fat_msg+0xb0/0xe0 fs/fat/misc.c:62
 __fat_fs_error+0x183/0x1e0 fs/fat/misc.c:31
 __fat_get_block fs/fat/inode.c:-1 [inline]
 fat_get_block+0x599/0x5e0 fs/fat/inode.c:190
 __block_write_full_folio+0x297/0x8f0 fs/buffer.c:1885
 block_write_full_folio+0x2c1/0x2e0 fs/buffer.c:-1
 mpage_write_folio fs/mpage.c:641 [inline]
 mpage_writepages+0x710/0x1310 fs/mpage.c:670
 fat_writepages+0x24/0x30 fs/fat/inode.c:200
 do_writepages+0x1c6/0x310 mm/page-writeback.c:2598
 filemap_writeback mm/filemap.c:387 [inline]
 filemap_fdatawrite_range mm/filemap.c:412 [inline]
 filemap_write_and_wait_range+0x166/0x370 mm/filemap.c:684
 filemap_invalidate_pages+0xd3/0x1e0 mm/filemap.c:2904
 kiocb_invalidate_pages mm/filemap.c:2923 [inline]
 generic_file_direct_write+0x9d/0x240 mm/filemap.c:4241
 __generic_file_write_iter+0xab/0x120 mm/filemap.c:4417
 generic_file_write_iter+0x8d/0x310 mm/filemap.c:4457
 new_sync_write fs/read_write.c:593 [inline]
 vfs_write+0x5a6/0x9f0 fs/read_write.c:686
 ksys_write+0xdc/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+0xc0/0x2a0 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

value changed: 0x000000010000cec9 -> 0x000000010000dfb6

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 UID: 0 PID: 25888 Comm: syz.0.21848 Tainted: G        W           syzkaller #0 PREEMPT(voluntary) 
Tainted: [W]=WARN
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/25/2025
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