KCSAN: data-race in data_alloc / prb_reserve

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: 0d02ec6b Linux 5.12-rc4
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=13a8dedcd00000
kernel config: https://syzkaller.appspot.com/x/.config?x=3fc18c5a751f4269
dashboard link: https://syzkaller.appspot.com/bug?extid=3ef70d22840405b8403f
compiler: Debian clang version 11.0.1-2
CC: [gre...@linuxfoundation.org linux-...@vger.kernel.org raf...@kernel.org]

Unfortunately, I don't have any reproducer for this issue yet.

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+3ef70d...@syzkaller.appspotmail.com

==================================================================
BUG: KCSAN: data-race in data_alloc / prb_reserve

write to 0xffffffff876afd60 of 8 bytes by task 31126 on cpu 0:
data_alloc+0x27e/0x2b0 kernel/printk/printk_ringbuffer.c:1085
prb_reserve+0x8f0/0xbc0 kernel/printk/printk_ringbuffer.c:1549
vprintk_store+0x3e9/0x9c0 kernel/printk/printk.c:2029
vprintk_emit+0xca/0x3e0 kernel/printk/printk.c:2081
dev_vprintk_emit+0x1c6/0x1ea drivers/base/core.c:4434
dev_printk_emit+0x6a/0x8c drivers/base/core.c:4445
__dev_printk+0xfa/0x103 drivers/base/core.c:4457
_dev_warn+0x76/0x96 drivers/base/core.c:4501
hub_port_init+0x13a5/0x18d0 drivers/usb/core/hub.c:4859
hub_port_connect drivers/usb/core/hub.c:5155 [inline]
hub_port_connect_change drivers/usb/core/hub.c:5363 [inline]
port_event drivers/usb/core/hub.c:5509 [inline]
hub_event+0x1a1e/0x2b60 drivers/usb/core/hub.c:5591
process_one_work+0x3e1/0x950 kernel/workqueue.c:2275
worker_thread+0x616/0xa70 kernel/workqueue.c:2421
kthread+0x20b/0x230 kernel/kthread.c:292
ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:294

read to 0xffffffff876afd60 of 8 bytes by task 9458 on cpu 1:
desc_read kernel/printk/printk_ringbuffer.c:477 [inline]
desc_push_tail kernel/printk/printk_ringbuffer.c:771 [inline]
desc_reserve kernel/printk/printk_ringbuffer.c:917 [inline]
prb_reserve+0x20c/0xbc0 kernel/printk/printk_ringbuffer.c:1499
vprintk_store+0x3e9/0x9c0 kernel/printk/printk.c:2029
vprintk_emit+0xca/0x3e0 kernel/printk/printk.c:2081
dev_vprintk_emit+0x1c6/0x1ea drivers/base/core.c:4434
dev_printk_emit+0x6a/0x8c drivers/base/core.c:4445
__dev_printk+0xfa/0x103 drivers/base/core.c:4457
_dev_info+0x76/0x96 drivers/base/core.c:4503
announce_device drivers/usb/core/hub.c:2281 [inline]
usb_new_device+0x39d/0xc60 drivers/usb/core/hub.c:2535
hub_port_connect drivers/usb/core/hub.c:5223 [inline]
hub_port_connect_change drivers/usb/core/hub.c:5363 [inline]
port_event drivers/usb/core/hub.c:5509 [inline]
hub_event+0x1d17/0x2b60 drivers/usb/core/hub.c:5591
process_one_work+0x3e1/0x950 kernel/workqueue.c:2275
worker_thread+0x616/0xa70 kernel/workqueue.c:2421
kthread+0x20b/0x230 kernel/kthread.c:292
ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:294

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 PID: 9458 Comm: kworker/1:6 Not tainted 5.12.0-rc4-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
Workqueue: usb_hub_wq hub_event
==================================================================


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