syzbot

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BUG: KCSAN: data-race in fat32_ent_put / fat_mirror_bhs

read-write to 0xffff888129571100 of 4 bytes by task 28102 on cpu 0:
 fat32_ent_put+0x4e/0x90 fs/fat/fatent.c:194
 fat_ent_write+0x6c/0xe0 fs/fat/fatent.c:422
 fat_chain_add+0x172/0x490 fs/fat/misc.c:136
 fat_add_cluster fs/fat/inode.c:113 [inline]
 __fat_get_block fs/fat/inode.c:155 [inline]
 fat_get_block+0x475/0x5f0 fs/fat/inode.c:190
 __block_write_begin_int+0x400/0xf90 fs/buffer.c:2042
 block_write_begin fs/buffer.c:2153 [inline]
 cont_write_begin+0x5fe/0x970 fs/buffer.c:2491
 fat_write_begin+0x52/0xe0 fs/fat/inode.c:230
 cont_expand_zero fs/buffer.c:2419 [inline]
 cont_write_begin+0x1b0/0x970 fs/buffer.c:2481
 fat_write_begin+0x52/0xe0 fs/fat/inode.c:230
 generic_perform_write+0x183/0x490 mm/filemap.c:4325
 __generic_file_write_iter+0xec/0x120 mm/filemap.c:4439
 generic_file_write_iter+0x8d/0x310 mm/filemap.c:4468
 do_iter_readv_writev+0x4fd/0x5a0 fs/read_write.c:-1
 vfs_writev+0x2e1/0x900 fs/read_write.c:1059
 do_pwritev fs/read_write.c:1155 [inline]
 __do_sys_pwritev2 fs/read_write.c:1213 [inline]
 __se_sys_pwritev2+0xfc/0x1c0 fs/read_write.c:1204
 __x64_sys_pwritev2+0x67/0x80 fs/read_write.c:1204
 x64_sys_call+0xe07/0x3020 arch/x86/include/generated/asm/syscalls_64.h:329
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0x12c/0x3b0 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

read to 0xffff888129571000 of 512 bytes by task 28111 on cpu 1:
 fat_mirror_bhs+0x1df/0x330 fs/fat/fatent.c:399
 fat_ent_write+0xd0/0xe0 fs/fat/fatent.c:428
 fat_chain_add+0x172/0x490 fs/fat/misc.c:136
 fat_add_entries+0xdbb/0x10b0 fs/fat/dir.c:1399
 vfat_add_entry+0x2103/0x2280 fs/fat/namei_vfat.c:675
 vfat_rename fs/fat/namei_vfat.c:971 [inline]
 vfat_rename2+0x81d/0x13f0 fs/fat/namei_vfat.c:1176
 vfs_rename+0x97f/0xad0 fs/namei.c:6054
 filename_renameat2+0x3b6/0x6e0 fs/namei.c:6172
 __do_sys_renameat2 fs/namei.c:6201 [inline]
 __se_sys_renameat2+0x4f/0x1c0 fs/namei.c:6196
 __x64_sys_renameat2+0x67/0x80 fs/namei.c:6196
 x64_sys_call+0x2a12/0x3020 arch/x86/include/generated/asm/syscalls_64.h:317
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0x12c/0x3b0 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: 28111 Comm: syz.8.4663 Tainted: G        W           syzkaller #0 PREEMPT(full) 
Tainted: [W]=WARN
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 04/18/2026
==================================================================
bio_check_eod: 1 callbacks suppressed
syz.8.4663: attempt to access beyond end of device
loop8: rw=2049, sector=129, nr_sectors = 1 limit=128