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

write to 0xffffffff86c77bc0 of 8 bytes by task 24152 on cpu 1:
 data_alloc+0x310/0x390 kernel/printk/printk_ringbuffer.c:1129
 prb_reserve+0x8d7/0xae0 kernel/printk/printk_ringbuffer.c:1724
 vprintk_store+0x54a/0x910 kernel/printk/printk.c:2354
 vprintk_emit+0x1a4/0x600 kernel/printk/printk.c:2455
 vprintk_default+0x26/0x30 kernel/printk/printk.c:2494
 vprintk+0x1d/0x30 kernel/printk/printk_safe.c:82
 _printk+0x79/0xa0 kernel/printk/printk.c:2504
 _fat_msg+0xb0/0xe0 fs/fat/misc.c:62
 __fat_fs_error+0x183/0x1e0 fs/fat/misc.c:31
 __fat_get_block fs/fat/inode.c:-1 [inline]
 fat_get_block+0x599/0x5e0 fs/fat/inode.c:190
 mpage_write_folio fs/mpage.c:545 [inline]
 __mpage_writepages+0x503/0x1390 fs/mpage.c:687
 mpage_writepages include/linux/mpage.h:27 [inline]
 fat_writepages+0x26/0x30 fs/fat/inode.c:200
 do_writepages+0x1c6/0x310 mm/page-writeback.c:2554
 filemap_writeback mm/filemap.c:387 [inline]
 filemap_fdatawrite_range mm/filemap.c:412 [inline]
 filemap_fdatawrite+0x100/0x140 mm/filemap.c:418
 writeback_inode fs/fat/inode.c:1877 [inline]
 fat_flush_inodes+0xcc/0x150 fs/fat/inode.c:1895
 fat_truncate_blocks+0x528/0x5a0 fs/fat/file.c:396
 fat_write_failed fs/fat/inode.c:219 [inline]
 fat_write_begin+0xbd/0xe0 fs/fat/inode.c:234
 generic_cont_expand_simple+0xb0/0x150 fs/buffer.c:2482
 fat_cont_expand+0x3e/0x170 fs/fat/file.c:224
 fat_setattr+0x2a4/0x870 fs/fat/file.c:514
 notify_change+0x872/0x8f0 fs/attr.c:556
 do_truncate+0x14f/0x190 fs/open.c:68
 vfs_truncate+0x1e8/0x220 fs/open.c:118
 do_sys_truncate+0xa2/0x140 fs/open.c:142
 __do_sys_truncate fs/open.c:154 [inline]
 __se_sys_truncate fs/open.c:152 [inline]
 __x64_sys_truncate+0x31/0x40 fs/open.c:152
 x64_sys_call+0x19fb/0x3020 arch/x86/include/generated/asm/syscalls_64.h:77
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0x12c/0x370 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

read to 0xffffffff86c77bc0 of 16 bytes by task 2990 on cpu 0:
 desc_read kernel/printk/printk_ringbuffer.c:496 [inline]
 desc_read_finalized_seq kernel/printk/printk_ringbuffer.c:1931 [inline]
 prb_read kernel/printk/printk_ringbuffer.c:1979 [inline]
 _prb_read_valid+0x1bc/0x950 kernel/printk/printk_ringbuffer.c:2170
 prb_read_valid+0x3c/0x60 kernel/printk/printk_ringbuffer.c:2242
 syslog_print+0x258/0x560 kernel/printk/printk.c:1628
 do_syslog+0x52b/0x7f0 kernel/printk/printk.c:1763
 __do_sys_syslog kernel/printk/printk.c:1855 [inline]
 __se_sys_syslog kernel/printk/printk.c:1853 [inline]
 __x64_sys_syslog+0x41/0x50 kernel/printk/printk.c:1853
 x64_sys_call+0x2b9e/0x3020 arch/x86/include/generated/asm/syscalls_64.h:104
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0x12c/0x370 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 UID: 0 PID: 2990 Comm: klogd Tainted: G        W           syzkaller #0 PREEMPT(full) 
Tainted: [W]=WARN
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 02/12/2026
==================================================================
==================================================================
BUG: KCSAN: data-race in _prb_read_valid / data_alloc

write to 0xffffffff86c7b868 of 8 bytes by task 24152 on cpu 1:
 data_alloc+0x310/0x390 kernel/printk/printk_ringbuffer.c:1129
 prb_reserve+0x8d7/0xae0 kernel/printk/printk_ringbuffer.c:1724
 vprintk_store+0x54a/0x910 kernel/printk/printk.c:2354
 vprintk_emit+0x1a4/0x600 kernel/printk/printk.c:2455
 vprintk_default+0x26/0x30 kernel/printk/printk.c:2494
 vprintk+0x1d/0x30 kernel/printk/printk_safe.c:82
 _printk+0x79/0xa0 kernel/printk/printk.c:2504
 _fat_msg+0xb0/0xe0 fs/fat/misc.c:62
 __fat_fs_error+0x183/0x1e0 fs/fat/misc.c:31
 __fat_get_block fs/fat/inode.c:-1 [inline]
 fat_get_block+0x599/0x5e0 fs/fat/inode.c:190
 mpage_write_folio fs/mpage.c:545 [inline]
 __mpage_writepages+0x503/0x1390 fs/mpage.c:687
 mpage_writepages include/linux/mpage.h:27 [inline]
 fat_writepages+0x26/0x30 fs/fat/inode.c:200
 do_writepages+0x1c6/0x310 mm/page-writeback.c:2554
 filemap_writeback mm/filemap.c:387 [inline]
 filemap_fdatawrite_range mm/filemap.c:412 [inline]
 filemap_fdatawrite+0x100/0x140 mm/filemap.c:418
 writeback_inode fs/fat/inode.c:1877 [inline]
 fat_flush_inodes+0xcc/0x150 fs/fat/inode.c:1895
 fat_truncate_blocks+0x528/0x5a0 fs/fat/file.c:396
 fat_write_failed fs/fat/inode.c:219 [inline]
 fat_write_begin+0xbd/0xe0 fs/fat/inode.c:234
 generic_cont_expand_simple+0xb0/0x150 fs/buffer.c:2482
 fat_cont_expand+0x3e/0x170 fs/fat/file.c:224
 fat_setattr+0x2a4/0x870 fs/fat/file.c:514
 notify_change+0x872/0x8f0 fs/attr.c:556
 do_truncate+0x14f/0x190 fs/open.c:68
 vfs_truncate+0x1e8/0x220 fs/open.c:118
 do_sys_truncate+0xa2/0x140 fs/open.c:142
 __do_sys_truncate fs/open.c:154 [inline]
 __se_sys_truncate fs/open.c:152 [inline]
 __x64_sys_truncate+0x31/0x40 fs/open.c:152
 x64_sys_call+0x19fb/0x3020 arch/x86/include/generated/asm/syscalls_64.h:77
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0x12c/0x370 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

read to 0xffffffff86c7b868 of 16 bytes by task 2990 on cpu 0:
 desc_read kernel/printk/printk_ringbuffer.c:496 [inline]
 desc_read_finalized_seq kernel/printk/printk_ringbuffer.c:1931 [inline]
 prb_read kernel/printk/printk_ringbuffer.c:1979 [inline]
 _prb_read_valid+0x1bc/0x950 kernel/printk/printk_ringbuffer.c:2170
 prb_read_valid+0x3c/0x60 kernel/printk/printk_ringbuffer.c:2242
 syslog_print+0x109/0x560 kernel/printk/printk.c:1611
 do_syslog+0x52b/0x7f0 kernel/printk/printk.c:1763
 __do_sys_syslog kernel/printk/printk.c:1855 [inline]
 __se_sys_syslog kernel/printk/printk.c:1853 [inline]
 __x64_sys_syslog+0x41/0x50 kernel/printk/printk.c:1853
 x64_sys_call+0x2b9e/0x3020 arch/x86/include/generated/asm/syscalls_64.h:104
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0x12c/0x370 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 UID: 0 PID: 2990 Comm: klogd Tainted: G        W           syzkaller #0 PREEMPT(full) 
Tainted: [W]=WARN
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 02/12/2026
==================================================================