syzbot

loop7: p3 start 18548 is beyond EOD, 
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BUG: KCSAN: data-race in _prb_read_valid / prb_reserve

write to 0xffffffff86909b80 of 88 bytes by task 19101 on cpu 0:
 prb_reserve+0x696/0xaf0 kernel/printk/printk_ringbuffer.c:1635
 vprintk_store+0x56d/0x860 kernel/printk/printk.c:2326
 vprintk_emit+0x178/0x650 kernel/printk/printk.c:2426
 vprintk_default+0x26/0x30 kernel/printk/printk.c:2465
 vprintk+0x1d/0x30 kernel/printk/printk_safe.c:82
 _printk+0x79/0xa0 kernel/printk/printk.c:2475
 blk_add_partition block/partitions/core.c:540 [inline]
 blk_add_partitions block/partitions/core.c:633 [inline]
 bdev_disk_changed+0x821/0xcb0 block/partitions/core.c:693
 loop_reread_partitions drivers/block/loop.c:436 [inline]
 loop_set_status+0x516/0x5c0 drivers/block/loop.c:1263
 lo_ioctl+0x75b/0x15d0 drivers/block/loop.c:-1
 blkdev_ioctl+0x352/0x440 block/ioctl.c:704
 vfs_ioctl fs/ioctl.c:51 [inline]
 __do_sys_ioctl fs/ioctl.c:906 [inline]
 __se_sys_ioctl+0xcb/0x140 fs/ioctl.c:892
 __x64_sys_ioctl+0x43/0x50 fs/ioctl.c:892
 x64_sys_call+0x19a8/0x2fb0 arch/x86/include/generated/asm/syscalls_64.h:17
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0xd0/0x1a0 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

read to 0xffffffff86909b80 of 8 bytes by task 19108 on cpu 1:
 desc_read kernel/printk/printk_ringbuffer.c:486 [inline]
 prb_first_seq kernel/printk/printk_ringbuffer.c:1957 [inline]
 _prb_read_valid+0x383/0x920 kernel/printk/printk_ringbuffer.c:2114
 prb_read_valid+0x3c/0x60 kernel/printk/printk_ringbuffer.c:2185
 __console_flush_and_unlock kernel/printk/printk.c:3304 [inline]
 console_unlock+0x164/0x330 kernel/printk/printk.c:3325
 vprintk_emit+0x388/0x650 kernel/printk/printk.c:2450
 vprintk_default+0x26/0x30 kernel/printk/printk.c:2465
 vprintk+0x1d/0x30 kernel/printk/printk_safe.c:82
 _printk+0x79/0xa0 kernel/printk/printk.c:2475
 blk_add_partition block/partitions/core.c:540 [inline]
 blk_add_partitions block/partitions/core.c:633 [inline]
 bdev_disk_changed+0x821/0xcb0 block/partitions/core.c:693
 loop_reread_partitions drivers/block/loop.c:436 [inline]
 loop_set_status+0x516/0x5c0 drivers/block/loop.c:1263
 lo_ioctl+0x75b/0x15d0 drivers/block/loop.c:-1
 blkdev_ioctl+0x352/0x440 block/ioctl.c:704
 vfs_ioctl fs/ioctl.c:51 [inline]
 __do_sys_ioctl fs/ioctl.c:906 [inline]
 __se_sys_ioctl+0xcb/0x140 fs/ioctl.c:892
 __x64_sys_ioctl+0x43/0x50 fs/ioctl.c:892
 x64_sys_call+0x19a8/0x2fb0 arch/x86/include/generated/asm/syscalls_64.h:17
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0xd0/0x1a0 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

value changed: 0x00000000000034b8 -> 0x00000000000054b8

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 UID: 0 PID: 19108 Comm: syz.7.11695 Not tainted 6.15.0-rc7-syzkaller-00099-g94305e83eccb #0 PREEMPT(voluntary) 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 05/07/2025
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truncated