syzbot

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

write to 0xffffffff85c857b0 of 8 bytes by task 32270 on cpu 0:
 data_alloc+0x27e/0x2b0 kernel/printk/printk_ringbuffer.c:1088
 prb_reserve+0x897/0xbd0 kernel/printk/printk_ringbuffer.c:1555
 vprintk_store+0x51c/0xb50 kernel/printk/printk.c:2196
 vprintk_emit+0xcc/0x430 kernel/printk/printk.c:2252
 vprintk_default+0x22/0x30 kernel/printk/printk.c:2282
 vprintk+0x7f/0x90 kernel/printk/printk_safe.c:50
 _printk+0x76/0x96 kernel/printk/printk.c:2292
 __loop_clr_fd+0x3ba/0x3c0 drivers/block/loop.c:1193
 loop_clr_fd drivers/block/loop.c:1257 [inline]
 lo_ioctl+0xd8c/0x1290 drivers/block/loop.c:1563
 blkdev_ioctl+0x20e/0x440 block/ioctl.c:614
 vfs_ioctl fs/ioctl.c:51 [inline]
 __do_sys_ioctl fs/ioctl.c:870 [inline]
 __se_sys_ioctl+0xcb/0x140 fs/ioctl.c:856
 __x64_sys_ioctl+0x3f/0x50 fs/ioctl.c:856
 do_syscall_x64 arch/x86/entry/common.c:50 [inline]
 do_syscall_64+0x2b/0x70 arch/x86/entry/common.c:80
 entry_SYSCALL_64_after_hwframe+0x63/0xcd

read to 0xffffffff85c857b0 of 8 bytes by task 32273 on cpu 1:
 desc_read kernel/printk/printk_ringbuffer.c:478 [inline]
 desc_push_tail kernel/printk/printk_ringbuffer.c:774 [inline]
 desc_reserve kernel/printk/printk_ringbuffer.c:920 [inline]
 prb_reserve+0x224/0xbd0 kernel/printk/printk_ringbuffer.c:1505
 vprintk_store+0x51c/0xb50 kernel/printk/printk.c:2196
 vprintk_emit+0xcc/0x430 kernel/printk/printk.c:2252
 vprintk_default+0x22/0x30 kernel/printk/printk.c:2282
 vprintk+0x7f/0x90 kernel/printk/printk_safe.c:50
 _printk+0x76/0x96 kernel/printk/printk.c:2292
 blk_print_req_error+0x117/0x120 block/blk-mq.c:711
 blk_update_request+0x77c/0x850 block/blk-mq.c:809
 blk_mq_end_request block/blk-mq.c:951 [inline]
 blk_mq_plug_issue_direct+0x19f/0x5c0 block/blk-mq.c:2558
 blk_mq_flush_plug_list+0x27a/0x340 block/blk-mq.c:2639
 __blk_flush_plug+0x25a/0x2b0 block/blk-core.c:1153
 blk_finish_plug+0x44/0x60 block/blk-core.c:1177
 read_pages+0x71c/0x790 mm/readahead.c:181
 page_cache_ra_unbounded+0x2a8/0x2e0 mm/readahead.c:263
 do_page_cache_ra mm/readahead.c:293 [inline]
 force_page_cache_ra+0x1c6/0x200 mm/readahead.c:324
 page_cache_sync_ra+0xc8/0xf0 mm/readahead.c:695
 page_cache_sync_readahead include/linux/pagemap.h:1215 [inline]
 filemap_get_pages mm/filemap.c:2566 [inline]
 filemap_read+0x3ef/0x1430 mm/filemap.c:2660
 blkdev_read_iter+0x2c6/0x370 block/fops.c:598
 call_read_iter include/linux/fs.h:2181 [inline]
 new_sync_read fs/read_write.c:389 [inline]
 vfs_read+0x3a5/0x560 fs/read_write.c:470
 ksys_read+0xe8/0x1a0 fs/read_write.c:607
 __do_sys_read fs/read_write.c:617 [inline]
 __se_sys_read fs/read_write.c:615 [inline]
 __x64_sys_read+0x3e/0x50 fs/read_write.c:615
 do_syscall_x64 arch/x86/entry/common.c:50 [inline]
 do_syscall_64+0x2b/0x70 arch/x86/entry/common.c:80
 entry_SYSCALL_64_after_hwframe+0x63/0xcd

value changed: 0x00000000003b8d70 -> 0x000000000044ef28

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 PID: 32273 Comm: udevd Not tainted 6.0.0-rc6-syzkaller-00309-g1a61b828566f-dirty #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 08/26/2022
==================================================================
I/O error, dev loop1, sector 0 op 0x0:(READ) flags 0x80700 phys_seg 1 prio class 2
I/O error, dev loop1, sector 0 op 0x0:(READ) flags 0x0 phys_seg 1 prio class 2
Buffer I/O error on dev loop1p2, logical block 0, async page read
udevd[32273]: inotify_add_watch(7, /dev/loop1p2, 10) failed: No such file or directory
udevd[32273]: inotify_add_watch(7, /dev/loop1p2, 10) failed: No such file or directory