==================================================================
BUG: KCSAN: data-race in data_push_tail / string

write to 0xffffffff84159f02 of 1 bytes by task 29294 on cpu 0:
 string_nocheck lib/vsprintf.c:642 [inline]
 string+0xa1/0x210 lib/vsprintf.c:720
 vsnprintf+0xab0/0xed0 lib/vsprintf.c:2797
 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:257 [inline]
 loop_configure+0xb58/0xd10 drivers/block/loop.c:1243
 lo_ioctl+0x558/0x1210 drivers/block/loop.c:1781
 blkdev_ioctl+0x1d0/0x3c0 block/ioctl.c:585
 block_ioctl+0x6d/0x80 fs/block_dev.c:1602
 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 0xffffffff84159f00 of 8 bytes by task 29282 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
 fat_msg+0x80/0xaf fs/fat/misc.c:56
 fat_fill_super+0x1983/0x2a80 fs/fat/inode.c:1354
 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:610
 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_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: 0x00000000fffff73f -> 0x64203a34706f6f6c

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 PID: 29282 Comm: syz-executor.2 Not tainted 5.14.0-rc2-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
==================================================================