BUG: KCSAN: data-race in _prb_read_valid / data_alloc

write to 0xffffffff8688fc58 of 8 bytes by task 26282 on cpu 0:
 data_alloc+0x274/0x2e0 kernel/printk/printk_ringbuffer.c:1101
 prb_reserve+0x807/0xaf0 kernel/printk/printk_ringbuffer.c:1685
 vprintk_store+0x56d/0x860 kernel/printk/printk.c:2299
 vprintk_emit+0x10d/0x580 kernel/printk/printk.c:2399
 vprintk_default+0x26/0x30 kernel/printk/printk.c:2438
 vprintk+0x1d/0x30 kernel/printk/printk_safe.c:82
 _printk+0x79/0xa0 kernel/printk/printk.c:2448
 dump_stack_print_info+0xee/0x1b0 lib/dump_stack.c:57
 __dump_stack+0x11/0x30 lib/dump_stack.c:93
 dump_stack_lvl+0xe8/0x140 lib/dump_stack.c:120
 dump_stack+0x15/0x1b lib/dump_stack.c:129
 fail_dump lib/fault-inject.c:73 [inline]
 should_fail_ex+0x265/0x280 lib/fault-inject.c:174
 should_fail+0xb/0x20 lib/fault-inject.c:184
 should_fail_usercopy+0x1a/0x20 lib/fault-inject-usercopy.c:35
 strncpy_from_user+0x25/0x230 lib/strncpy_from_user.c:118
 getname_flags+0xae/0x3b0 fs/namei.c:157
 getname include/linux/fs.h:2921 [inline]
 __do_sys_unlinkat fs/namei.c:-1 [inline]
 __se_sys_unlinkat fs/namei.c:4771 [inline]
 __x64_sys_unlinkat+0x70/0xb0 fs/namei.c:4771
 x64_sys_call+0x2eed/0x3000 arch/x86/include/generated/asm/syscalls_64.h:264
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0xd2/0x200 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

read to 0xffffffff8688fc58 of 16 bytes by task 26263 on cpu 1:
 desc_read kernel/printk/printk_ringbuffer.c:479 [inline]
 desc_read_finalized_seq kernel/printk/printk_ringbuffer.c:1892 [inline]
 prb_read kernel/printk/printk_ringbuffer.c:1940 [inline]
 _prb_read_valid+0x1bc/0x920 kernel/printk/printk_ringbuffer.c:2131
 desc_update_last_finalized kernel/printk/printk_ringbuffer.c:1531 [inline]
 prb_final_commit+0x136/0x1e0 kernel/printk/printk_ringbuffer.c:1800
 vprintk_store+0x7c4/0x860 kernel/printk/printk.c:2283
 vprintk_emit+0x10d/0x580 kernel/printk/printk.c:2399
 vprintk_default+0x26/0x30 kernel/printk/printk.c:2438
 vprintk+0x1d/0x30 kernel/printk/printk_safe.c:82
 _printk+0x79/0xa0 kernel/printk/printk.c:2448
 __ext4_grp_locked_error+0x5d0/0x7b0 fs/ext4/super.c:1063
 ext4_mb_generate_buddy+0x240/0x2c0 fs/ext4/mballoc.c:1286
 ext4_mb_init_cache+0x847/0xba0 fs/ext4/mballoc.c:1475
 ext4_mb_init_group+0x25b/0x3f0 fs/ext4/mballoc.c:1612
 ext4_mb_good_group_nolock fs/ext4/mballoc.c:2797 [inline]
 ext4_mb_scan_group+0x5f4/0xf10 fs/ext4/mballoc.c:2934
 ext4_mb_scan_groups_linear fs/ext4/mballoc.c:1146 [inline]
 ext4_mb_scan_groups fs/ext4/mballoc.c:1180 [inline]
 ext4_mb_regular_allocator+0x70a/0x15e0 fs/ext4/mballoc.c:3026
 ext4_mb_new_blocks+0x800/0x2080 fs/ext4/mballoc.c:6295
 ext4_ext_map_blocks+0xff5/0x38a0 fs/ext4/extents.c:4383
 ext4_map_create_blocks fs/ext4/inode.c:609 [inline]
 ext4_map_blocks+0x5ee/0xd00 fs/ext4/inode.c:811
 mpage_map_one_extent fs/ext4/inode.c:2374 [inline]
 mpage_map_and_submit_extent fs/ext4/inode.c:2468 [inline]
 ext4_do_writepages+0x15e1/0x2750 fs/ext4/inode.c:2931
 ext4_writepages+0x176/0x300 fs/ext4/inode.c:3025
 do_writepages+0x1c3/0x310 mm/page-writeback.c:2604
 filemap_fdatawrite_wbc mm/filemap.c:389 [inline]
 __filemap_fdatawrite_range mm/filemap.c:422 [inline]
 file_write_and_wait_range+0x156/0x2c0 mm/filemap.c:797
 generic_buffers_fsync_noflush+0x45/0x120 fs/buffer.c:609
 ext4_fsync_nojournal fs/ext4/fsync.c:88 [inline]
 ext4_sync_file+0x1ab/0x690 fs/ext4/fsync.c:147
 vfs_fsync_range+0x10d/0x130 fs/sync.c:187
 generic_write_sync include/linux/fs.h:3045 [inline]
 ext4_buffered_write_iter+0x34f/0x3c0 fs/ext4/file.c:305
 ext4_file_write_iter+0x387/0xf60 fs/ext4/file.c:-1
 new_sync_write fs/read_write.c:593 [inline]
 vfs_write+0x527/0x960 fs/read_write.c:686
 ksys_write+0xda/0x1a0 fs/read_write.c:738
 __do_sys_write fs/read_write.c:749 [inline]
 __se_sys_write fs/read_write.c:746 [inline]
 __x64_sys_write+0x40/0x50 fs/read_write.c:746
 x64_sys_call+0x2802/0x3000 arch/x86/include/generated/asm/syscalls_64.h:2
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0xd2/0x200 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 UID: 0 PID: 26263 Comm: syz.4.7724 Not tainted syzkaller #0 PREEMPT(voluntary) 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 08/18/2025
==================================================================
EXT4-fs (loop4): Delayed block allocation failed for inode 18 at logical offset 0 with max blocks 2048 with error 28
EXT4-fs (loop4): This should not happen!! Data will be lost

EXT4-fs (loop4): Total free blocks count 0
EXT4-fs (loop4): Free/Dirty block details
EXT4-fs (loop4): free_blocks=2415919104
EXT4-fs (loop4): dirty_blocks=8208
EXT4-fs (loop4): Block reservation details
EXT4-fs (loop4): i_reserved_data_blocks=513