BUG: KCSAN: data-race in data_push_tail / vsnprintf

write to 0xffffffff8450d2dc of 1 bytes by task 1034 on cpu 1:
 vsnprintf+0xe8f/0xed0 lib/vsprintf.c:2824
 vscnprintf+0x29/0x80 lib/vsprintf.c:2855
 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
 disk_unlock_native_capacity block/partitions/core.c:531 [inline]
 blk_add_partition block/partitions/core.c:575 [inline]
 blk_add_partitions+0x759/0xa80 block/partitions/core.c:653
 bdev_disk_changed+0x2d3/0x340 fs/block_dev.c:1274
 __blkdev_get+0x36d/0x6d0 fs/block_dev.c:1358
 blkdev_get_by_dev+0x9b/0x480 fs/block_dev.c:1451
 blkdev_reread_part block/ioctl.c:102 [inline]
 blkdev_common_ioctl+0xfca/0x1040 block/ioctl.c:510
 blkdev_ioctl+0x16e/0x3c0 block/ioctl.c:579
 block_ioctl+0x6d/0x80 fs/block_dev.c:1662
 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_64+0x4a/0x90 arch/x86/entry/common.c:47
 entry_SYSCALL_64_after_hwframe+0x44/0xae

read to 0xffffffff8450d2d8 of 8 bytes by task 29843 on cpu 0:
 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
 fat_msg+0x80/0xaf fs/fat/misc.c:56
 fat_fill_super+0x2892/0x2a80 fs/fat/inode.c:1890
 vfat_fill_super+0x2c/0x40 fs/fat/namei_vfat.c:1051
 mount_bdev+0x1e8/0x290 fs/super.c:1368
 vfat_mount+0x2d/0x40 fs/fat/namei_vfat.c:1058
 legacy_get_tree+0x70/0xc0 fs/fs_context.c:592
 vfs_get_tree+0x4a/0x1a0 fs/super.c:1498
 do_new_mount fs/namespace.c:2905 [inline]
 path_mount+0x11d4/0x1ce0 fs/namespace.c:3235
 do_mount fs/namespace.c:3248 [inline]
 __do_sys_mount fs/namespace.c:3456 [inline]
 __se_sys_mount+0x23d/0x2e0 fs/namespace.c:3433
 __x64_sys_mount+0x63/0x70 fs/namespace.c:3433
 do_syscall_64+0x4a/0x90 arch/x86/entry/common.c:47
 entry_SYSCALL_64_after_hwframe+0x44/0xae

value changed: 0x0000000100039c7e -> 0x000000000a646564

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 PID: 29843 Comm: syz-executor.3 Not tainted 5.13.0-rc6-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
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