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BUG: KCSAN: data-race in data_push_tail / vsnprintf

write to 0xffffffff841498b9 of 1 bytes by task 17210 on cpu 0:
 vsnprintf+0xe8f/0xed0 lib/vsprintf.c:2869
 vscnprintf+0x29/0x80 lib/vsprintf.c:2900
 printk_sprint kernel/printk/printk.c:2012 [inline]
 vprintk_store+0x4c1/0x9c0 kernel/printk/printk.c:2115
 vprintk_emit+0xca/0x3d0 kernel/printk/printk.c:2157
 vprintk_default+0x22/0x30 kernel/printk/printk.c:2185
 vprintk+0x15a/0x170 kernel/printk/printk_safe.c:392
 printk+0x62/0x87 kernel/printk/printk.c:2216
 set_capacity_and_notify+0x15a/0x1c0 block/genhd.c:66
 loop_set_size drivers/block/loop.c:298 [inline]
 loop_configure+0xc8e/0xeb0 drivers/block/loop.c:1295
 lo_ioctl+0x59b/0x1340 drivers/block/loop.c:1847
 blkdev_ioctl+0x1d0/0x3c0 block/ioctl.c:585
 block_ioctl+0x6d/0x80 fs/block_dev.c:1604
 vfs_ioctl fs/ioctl.c:51 [inline]
 __do_sys_ioctl fs/ioctl.c:1069 [inline]
 __se_sys_ioctl+0xcb/0x140 fs/ioctl.c:1055
 __x64_sys_ioctl+0x3f/0x50 fs/ioctl.c:1055
 do_syscall_x64 arch/x86/entry/common.c:50 [inline]
 do_syscall_64+0x3d/0x90 arch/x86/entry/common.c:80
 entry_SYSCALL_64_after_hwframe+0x44/0xae

read to 0xffffffff841498b8 of 8 bytes by task 17208 on cpu 1:
 data_make_reusable kernel/printk/printk_ringbuffer.c:587 [inline]
 data_push_tail+0x125/0x460 kernel/printk/printk_ringbuffer.c:672
 data_alloc+0xbc/0x2b0 kernel/printk/printk_ringbuffer.c:1043
 prb_reserve+0x8f0/0xbc0 kernel/printk/printk_ringbuffer.c:1549
 vprintk_store+0x3e9/0x9c0 kernel/printk/printk.c:2105
 vprintk_emit+0xca/0x3d0 kernel/printk/printk.c:2157
 vprintk_default+0x22/0x30 kernel/printk/printk.c:2185
 vprintk+0x15a/0x170 kernel/printk/printk_safe.c:392
 printk+0x62/0x87 kernel/printk/printk.c:2216
 set_capacity_and_notify+0x15a/0x1c0 block/genhd.c:66
 loop_set_size drivers/block/loop.c:298 [inline]
 loop_configure+0xc8e/0xeb0 drivers/block/loop.c:1295
 lo_ioctl+0x59b/0x1340 drivers/block/loop.c:1847
 blkdev_ioctl+0x1d0/0x3c0 block/ioctl.c:585
 block_ioctl+0x6d/0x80 fs/block_dev.c:1604
 vfs_ioctl fs/ioctl.c:51 [inline]
 __do_sys_ioctl fs/ioctl.c:1069 [inline]
 __se_sys_ioctl+0xcb/0x140 fs/ioctl.c:1055
 __x64_sys_ioctl+0x3f/0x50 fs/ioctl.c:1055
 do_syscall_x64 arch/x86/entry/common.c:50 [inline]
 do_syscall_64+0x3d/0x90 arch/x86/entry/common.c:80
 entry_SYSCALL_64_after_hwframe+0x44/0xae

value changed: 0x000000010001336f -> 0x000000010001000a

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 PID: 17208 Comm: syz-executor.2 Not tainted 5.14.0-rc5-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
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