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BUG: KCSAN: data-race in data_alloc / prb_reserve

write to 0xffffffff8686ce00 of 8 bytes by task 12 on cpu 0:
 data_alloc+0x280/0x2e0 kernel/printk/printk_ringbuffer.c:1102
 prb_reserve+0x807/0xaf0 kernel/printk/printk_ringbuffer.c:1685
 vprintk_store+0x56d/0x860 kernel/printk/printk.c:2299
 vprintk_emit+0x10d/0x580 kernel/printk/printk.c:2399
 vprintk_default+0x26/0x30 kernel/printk/printk.c:2438
 vprintk+0x1d/0x30 kernel/printk/printk_safe.c:82
 _printk+0x79/0xa0 kernel/printk/printk.c:2448
 __ext4_msg+0x18f/0x1a0 fs/ext4/super.c:990
 ext4_quota_write+0x109/0x360 fs/ext4/super.c:-1
 write_blk fs/quota/quota_tree.c:70 [inline]
 remove_free_dqentry+0x5ab/0x670 fs/quota/quota_tree.c:203
 free_dqentry fs/quota/quota_tree.c:507 [inline]
 remove_tree+0x8ae/0x1120 fs/quota/quota_tree.c:577
 remove_tree+0x633/0x1120 fs/quota/quota_tree.c:581
 remove_tree+0x633/0x1120 fs/quota/quota_tree.c:581
 remove_tree+0x633/0x1120 fs/quota/quota_tree.c:581
 qtree_delete_dquot fs/quota/quota_tree.c:617 [inline]
 qtree_release_dquot+0x16e/0x180 fs/quota/quota_tree.c:787
 v2_release_dquot+0x98/0xd0 fs/quota/quota_v2.c:391
 dquot_release+0x10b/0x210 fs/quota/dquot.c:540
 ext4_release_dquot+0x1e4/0x460 fs/ext4/super.c:-1
 quota_release_workfn+0x256/0x530 fs/quota/dquot.c:843
 process_one_work kernel/workqueue.c:3263 [inline]
 process_scheduled_works+0x4ce/0x9d0 kernel/workqueue.c:3346
 worker_thread+0x582/0x770 kernel/workqueue.c:3427
 kthread+0x489/0x510 kernel/kthread.c:463
 ret_from_fork+0x122/0x1b0 arch/x86/kernel/process.c:158
 ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245

read to 0xffffffff8686ce00 of 8 bytes by task 12217 on cpu 1:
 desc_read kernel/printk/printk_ringbuffer.c:479 [inline]
 desc_push_tail kernel/printk/printk_ringbuffer.c:775 [inline]
 desc_reserve kernel/printk/printk_ringbuffer.c:921 [inline]
 prb_reserve+0x220/0xaf0 kernel/printk/printk_ringbuffer.c:1635
 vprintk_store+0x56d/0x860 kernel/printk/printk.c:2299
 vprintk_emit+0x10d/0x580 kernel/printk/printk.c:2399
 vprintk_default+0x26/0x30 kernel/printk/printk.c:2438
 vprintk+0x1d/0x30 kernel/printk/printk_safe.c:82
 _printk+0x79/0xa0 kernel/printk/printk.c:2448
 set_capacity_and_notify+0x14c/0x1f0 block/genhd.c:93
 loop_set_size+0x2e/0x70 drivers/block/loop.c:220
 loop_configure+0x825/0x9c0 drivers/block/loop.c:1077
 lo_ioctl+0x1e1/0x12b0 drivers/block/loop.c:1532
 blkdev_ioctl+0x353/0x440 block/ioctl.c:705
 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+0x1816/0x3000 arch/x86/include/generated/asm/syscalls_64.h:17
 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: 0xfffffffffffcdb40 -> 0x000000000006f658

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 UID: 0 PID: 12217 Comm: syz.3.3197 Not tainted syzkaller #0 PREEMPT(voluntary) 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 08/18/2025
==================================================================
loop3: detected capacity change from 0 to 128