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BUG: KCSAN: data-race in _prb_read_valid / data_alloc

write to 0xffffffff86c87b50 of 8 bytes by task 9396 on cpu 0:
 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_cluster+0x7fa/0x820 fs/fat/cache.c:-1
 fat_bmap_cluster fs/fat/cache.c:294 [inline]
 fat_get_mapped_cluster+0xe4/0x240 fs/fat/cache.c:315
 fat_bmap+0x254/0x280 fs/fat/cache.c:379
 __fat_get_block fs/fat/inode.c:129 [inline]
 fat_get_block+0xd3/0x5e0 fs/fat/inode.c:190
 do_mpage_readpage+0x40b/0xe00 fs/mpage.c:222
 mpage_readahead+0x1c4/0x2e0 fs/mpage.c:371
 fat_readahead+0x1c/0x30 fs/fat/inode.c:210
 read_pages+0xa3/0x480 mm/readahead.c:163
 page_cache_ra_unbounded+0x357/0x450 mm/readahead.c:304
 do_page_cache_ra mm/readahead.c:334 [inline]
 page_cache_ra_order+0x153/0x250 mm/readahead.c:538
 do_sync_mmap_readahead+0x33d/0x350 mm/filemap.c:3405
 filemap_fault+0x362/0xb90 mm/filemap.c:3554
 __do_fault+0xbc/0x200 mm/memory.c:5364
 do_read_fault mm/memory.c:5799 [inline]
 do_fault mm/memory.c:5933 [inline]
 do_pte_missing mm/memory.c:4477 [inline]
 handle_pte_fault mm/memory.c:6317 [inline]
 __handle_mm_fault mm/memory.c:6455 [inline]
 handle_mm_fault+0x11d7/0x3020 mm/memory.c:6624
 faultin_page mm/gup.c:1126 [inline]
 __get_user_pages+0x1023/0x1ea0 mm/gup.c:1428
 populate_vma_page_range mm/gup.c:1860 [inline]
 __mm_populate+0x242/0x390 mm/gup.c:1963
 mm_populate include/linux/mm.h:3899 [inline]
 vm_mmap_pgoff+0x23b/0x2d0 mm/util.c:586
 ksys_mmap_pgoff+0x267/0x310 mm/mmap.c:605
 x64_sys_call+0x14df/0x3020 arch/x86/include/generated/asm/syscalls_64.h:10
 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 0xffffffff86c87b50 of 16 bytes by task 2987 on cpu 1:
 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+0x164/0x560 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: 1 UID: 0 PID: 2987 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
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