syzbot

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BUG: KCSAN: data-race in _copy_to_iter / fat16_ent_put

write to 0xffff88813d92115c of 2 bytes by task 3380 on cpu 0:
 fat16_ent_put+0x28/0x60 fs/fat/fatent.c:183
 fat_alloc_clusters+0x4c9/0xa80 fs/fat/fatent.c:503
 fat_add_cluster fs/fat/inode.c:108 [inline]
 __fat_get_block fs/fat/inode.c:155 [inline]
 fat_get_block+0x25c/0x5e0 fs/fat/inode.c:190
 __block_write_begin_int+0x417/0xfa0 fs/buffer.c:2128
 __block_write_begin fs/buffer.c:2177 [inline]
 block_write_begin+0x7b/0x170 fs/buffer.c:2236
 cont_write_begin+0x486/0x6b0 fs/buffer.c:2590
 fat_write_begin+0x61/0xf0 fs/fat/inode.c:230
 generic_perform_write+0x1d5/0x410 mm/filemap.c:4015
 __generic_file_write_iter+0xec/0x120 mm/filemap.c:4107
 generic_file_write_iter+0x7d/0x1d0 mm/filemap.c:4136
 new_sync_write fs/read_write.c:497 [inline]
 vfs_write+0x78f/0x900 fs/read_write.c:590
 ksys_write+0xeb/0x1b0 fs/read_write.c:643
 __do_sys_write fs/read_write.c:655 [inline]
 __se_sys_write fs/read_write.c:652 [inline]
 __x64_sys_write+0x42/0x50 fs/read_write.c:652
 x64_sys_call+0x27ef/0x2d70 arch/x86/include/generated/asm/syscalls_64.h:2
 do_syscall_x64 arch/x86/entry/common.c:52 [inline]
 do_syscall_64+0xc9/0x1c0 arch/x86/entry/common.c:83
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

read to 0xffff88813d921000 of 512 bytes by task 3386 on cpu 1:
 instrument_copy_to_user include/linux/instrumented.h:113 [inline]
 copy_to_user_iter lib/iov_iter.c:24 [inline]
 iterate_ubuf include/linux/iov_iter.h:29 [inline]
 iterate_and_advance2 include/linux/iov_iter.h:245 [inline]
 iterate_and_advance include/linux/iov_iter.h:271 [inline]
 _copy_to_iter+0x126/0xaf0 lib/iov_iter.c:185
 copy_page_to_iter+0x171/0x2b0 lib/iov_iter.c:362
 copy_folio_to_iter include/linux/uio.h:180 [inline]
 filemap_read+0x42c/0x690 mm/filemap.c:2676
 blkdev_read_iter+0x217/0x2c0 block/fops.c:749
 new_sync_read fs/read_write.c:395 [inline]
 vfs_read+0x5e6/0x6e0 fs/read_write.c:476
 ksys_read+0xeb/0x1b0 fs/read_write.c:619
 __do_sys_read fs/read_write.c:629 [inline]
 __se_sys_read fs/read_write.c:627 [inline]
 __x64_sys_read+0x42/0x50 fs/read_write.c:627
 x64_sys_call+0x27e5/0x2d70 arch/x86/include/generated/asm/syscalls_64.h:1
 do_syscall_x64 arch/x86/entry/common.c:52 [inline]
 do_syscall_64+0xc9/0x1c0 arch/x86/entry/common.c:83
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 PID: 3386 Comm: udevd Not tainted 6.10.0-rc5-syzkaller-00018-g55027e689933 #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 06/07/2024
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