syzbot

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BUG: KCSAN: data-race in _copy_to_iter / fat12_ent_put

write to 0xffff88813a70580c of 1 bytes by task 4605 on cpu 1:
 fat12_ent_put+0x7a/0x180 fs/fat/fatent.c:168
 fat_ent_write+0x62/0xe0 fs/fat/fatent.c:417
 fat_chain_add+0x15f/0x400 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+0x467/0x5e0 fs/fat/inode.c:190
 __block_write_begin_int+0x3b0/0xf50 fs/buffer.c:2064
 __block_write_begin fs/buffer.c:2114 [inline]
 block_write_begin+0x7c/0x180 fs/buffer.c:2175
 cont_write_begin+0x4c0/0x6f0 fs/buffer.c:2534
 fat_write_begin+0x61/0xf0 fs/fat/inode.c:230
 cont_expand_zero fs/buffer.c:2461 [inline]
 cont_write_begin+0x18f/0x6f0 fs/buffer.c:2524
 fat_write_begin+0x61/0xf0 fs/fat/inode.c:230
 generic_cont_expand_simple+0xad/0x140 fs/buffer.c:2425
 fat_cont_expand+0x3a/0x160 fs/fat/file.c:223
 fat_setattr+0x2a9/0x840 fs/fat/file.c:513
 notify_change+0x8c3/0x930 fs/attr.c:483
 do_truncate+0x116/0x150 fs/open.c:66
 do_sys_ftruncate+0x2a8/0x3a0 fs/open.c:194
 __do_sys_ftruncate fs/open.c:205 [inline]
 __se_sys_ftruncate fs/open.c:203 [inline]
 __x64_sys_ftruncate+0x33/0x40 fs/open.c:203
 do_syscall_x64 arch/x86/entry/common.c:50 [inline]
 do_syscall_64+0x41/0xc0 arch/x86/entry/common.c:80
 entry_SYSCALL_64_after_hwframe+0x63/0xcd

read to 0xffff88813a705800 of 1024 bytes by task 4540 on cpu 0:
 instrument_copy_to_user include/linux/instrumented.h:113 [inline]
 copyout lib/iov_iter.c:169 [inline]
 _copy_to_iter+0x142/0x940 lib/iov_iter.c:536
 copy_page_to_iter+0x1a8/0x310 lib/iov_iter.c:742
 copy_folio_to_iter include/linux/uio.h:197 [inline]
 filemap_read+0x438/0x680 mm/filemap.c:2742
 blkdev_read_iter+0x2ca/0x370 block/fops.c:606
 call_read_iter include/linux/fs.h:1862 [inline]
 new_sync_read fs/read_write.c:389 [inline]
 vfs_read+0x3b7/0x580 fs/read_write.c:470
 ksys_read+0xeb/0x1a0 fs/read_write.c:613
 __do_sys_read fs/read_write.c:623 [inline]
 __se_sys_read fs/read_write.c:621 [inline]
 __x64_sys_read+0x42/0x50 fs/read_write.c:621
 do_syscall_x64 arch/x86/entry/common.c:50 [inline]
 do_syscall_64+0x41/0xc0 arch/x86/entry/common.c:80
 entry_SYSCALL_64_after_hwframe+0x63/0xcd

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 PID: 4540 Comm: udevd Not tainted 6.4.0-rc3-syzkaller-00291-g4e893b5aa4ac #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 05/25/2023
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