syzbot

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BUG: KCSAN: data-race in _copy_to_iter / fat32_ent_put

read-write to 0xffff88811c3ee074 of 4 bytes by task 18099 on cpu 1:
 fat32_ent_put+0x4e/0x90 fs/fat/fatent.c:194
 fat_alloc_clusters+0x55e/0xc40 fs/fat/fatent.c:508
 fat_alloc_new_dir+0xbb/0x550 fs/fat/dir.c:1159
 vfat_mkdir+0xa4/0x210 fs/fat/namei_vfat.c:862
 vfs_mkdir+0x28a/0x3e0 fs/namei.c:5272
 filename_mkdirat+0x138/0x300 fs/namei.c:5305
 __do_sys_mkdir fs/namei.c:5332 [inline]
 __se_sys_mkdir+0x31/0xf0 fs/namei.c:5329
 __x64_sys_mkdir+0x31/0x40 fs/namei.c:5329
 x64_sys_call+0x2eab/0x3020 arch/x86/include/generated/asm/syscalls_64.h:84
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0x136/0x3c0 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

read to 0xffff88811c3ee000 of 512 bytes by task 3620 on cpu 0:
 instrument_copy_to_user include/linux/instrumented.h:130 [inline]
 copy_to_user_iter lib/iov_iter.c:24 [inline]
 iterate_ubuf include/linux/iov_iter.h:30 [inline]
 iterate_and_advance2 include/linux/iov_iter.h:302 [inline]
 iterate_and_advance include/linux/iov_iter.h:330 [inline]
 _copy_to_iter+0x130/0xea0 lib/iov_iter.c:197
 copy_page_to_iter+0x174/0x210 lib/iov_iter.c:374
 copy_folio_to_iter include/linux/uio.h:204 [inline]
 filemap_read+0x3ed/0xa20 mm/filemap.c:2865
 blkdev_read_iter+0x21e/0x2d0 block/fops.c:830
 new_sync_read fs/read_write.c:493 [inline]
 vfs_read+0x699/0x7c0 fs/read_write.c:574
 ksys_read+0xdc/0x1a0 fs/read_write.c:716
 __do_sys_read fs/read_write.c:725 [inline]
 __se_sys_read fs/read_write.c:723 [inline]
 __x64_sys_read+0x40/0x50 fs/read_write.c:723
 x64_sys_call+0x2886/0x3020 arch/x86/include/generated/asm/syscalls_64.h:1
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0x136/0x3c0 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: 3620 Comm: udevd Tainted: G        W           syzkaller #0 PREEMPT(lazy) 
Tainted: [W]=WARN
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 05/09/2026
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