syzbot

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BUG: KCSAN: data-race in copy_page_to_iter / fat16_ent_put

write to 0xffff8881278a520c of 2 bytes by task 12747 on cpu 0:
 fat16_ent_put+0x24/0x50 fs/fat/fatent.c:183
 fat_alloc_clusters+0x47d/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+0x263/0x600 fs/fat/inode.c:190
 __block_write_begin_int+0x33d/0xc90 fs/buffer.c:2006
 __block_write_begin fs/buffer.c:2056 [inline]
 block_write_begin+0x73/0x170 fs/buffer.c:2117
 cont_write_begin+0x3f1/0x520 fs/buffer.c:2468
 fat_write_begin+0x5d/0xe0 fs/fat/inode.c:235
 cont_expand_zero fs/buffer.c:2395 [inline]
 cont_write_begin+0x1a0/0x520 fs/buffer.c:2458
 fat_write_begin+0x5d/0xe0 fs/fat/inode.c:235
 generic_cont_expand_simple+0xa9/0x140 fs/buffer.c:2359
 fat_cont_expand+0x3a/0x160 fs/fat/file.c:222
 fat_setattr+0x34a/0x880 fs/fat/file.c:511
 notify_change+0x8e6/0xa00 fs/attr.c:424
 do_truncate fs/open.c:65 [inline]
 do_sys_ftruncate+0x317/0x420 fs/open.c:193
 __do_sys_ftruncate fs/open.c:204 [inline]
 __se_sys_ftruncate fs/open.c:202 [inline]
 __x64_sys_ftruncate+0x2f/0x40 fs/open.c:202
 do_syscall_x64 arch/x86/entry/common.c:50 [inline]
 do_syscall_64+0x2b/0x70 arch/x86/entry/common.c:80
 entry_SYSCALL_64_after_hwframe+0x63/0xcd

read to 0xffff8881278a5000 of 1377 bytes by task 1920 on cpu 1:
 instrument_copy_to_user include/linux/instrumented.h:119 [inline]
 copyout lib/iov_iter.c:154 [inline]
 copy_page_to_iter_iovec lib/iov_iter.c:226 [inline]
 __copy_page_to_iter lib/iov_iter.c:852 [inline]
 copy_page_to_iter+0x415/0x7b0 lib/iov_iter.c:880
 copy_folio_to_iter include/linux/uio.h:153 [inline]
 filemap_read+0x117b/0x1410 mm/filemap.c:2739
 blkdev_read_iter+0x2c6/0x370 block/fops.c:594
 call_read_iter include/linux/fs.h:2052 [inline]
 new_sync_read fs/read_write.c:401 [inline]
 vfs_read+0x5a5/0x6a0 fs/read_write.c:482
 ksys_read+0xe8/0x1a0 fs/read_write.c:620
 __do_sys_read fs/read_write.c:630 [inline]
 __se_sys_read fs/read_write.c:628 [inline]
 __x64_sys_read+0x3e/0x50 fs/read_write.c:628
 do_syscall_x64 arch/x86/entry/common.c:50 [inline]
 do_syscall_64+0x2b/0x70 arch/x86/entry/common.c:80
 entry_SYSCALL_64_after_hwframe+0x63/0xcd

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 PID: 1920 Comm: udevd Not tainted 5.19.0-rc8-syzkaller-00146-ge65c6a46df94-dirty #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 07/22/2022
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I/O error, dev loop5, sector 0 op 0x0:(READ) flags 0x0 phys_seg 1 prio class 0
Buffer I/O error on dev loop5, logical block 0, async page read
I/O error, dev loop5, sector 0 op 0x0:(READ) flags 0x0 phys_seg 1 prio class 0
Buffer I/O error on dev loop5, logical block 0, async page read
 loop5: unable to read partition table
blk_print_req_error: 2 callbacks suppressed
I/O error, dev loop5, sector 0 op 0x0:(READ) flags 0x0 phys_seg 1 prio class 0
buffer_io_error: 2 callbacks suppressed
Buffer I/O error on dev loop5, logical block 0, async page read
I/O error, dev loop5, sector 0 op 0x0:(READ) flags 0x0 phys_seg 1 prio class 0
Buffer I/O error on dev loop5, logical block 0, async page read
I/O error, dev loop1, sector 0 op 0x0:(READ) flags 0x0 phys_seg 1 prio class 0
Buffer I/O error on dev loop1, logical block 0, async page read
I/O error, dev loop1, sector 0 op 0x0:(READ) flags 0x0 phys_seg 1 prio class 0
Buffer I/O error on dev loop1, logical block 0, async page read
I/O error, dev loop5, sector 0 op 0x0:(READ) flags 0x0 phys_seg 1 prio class 0
Buffer I/O error on dev loop5, logical block 0, async page read
I/O error, dev loop5, sector 0 op 0x0:(READ) flags 0x80700 phys_seg 1 prio class 0