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BUG: KCSAN: data-race in __mpage_writepage / generic_write_end

write to 0xffff888109ee10e8 of 8 bytes by task 12850 on cpu 0:
 i_size_write include/linux/fs.h:905 [inline]
 generic_write_end+0xb4/0x360 fs/buffer.c:2241
 fat_write_end+0x4e/0x160 fs/fat/inode.c:244
 cont_expand_zero fs/buffer.c:2466 [inline]
 cont_write_begin+0x2d4/0x6f0 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_fallocate+0x182/0x1d0 fs/fat/file.c:301
 vfs_fallocate+0x369/0x3d0 fs/open.c:324
 ksys_fallocate fs/open.c:347 [inline]
 __do_sys_fallocate fs/open.c:355 [inline]
 __se_sys_fallocate fs/open.c:353 [inline]
 __x64_sys_fallocate+0x79/0xc0 fs/open.c:353
 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 0xffff888109ee10e8 of 8 bytes by task 12852 on cpu 1:
 i_size_read include/linux/fs.h:883 [inline]
 __mpage_writepage+0xc3/0xdb0 fs/mpage.c:489
 write_cache_pages+0x3a1/0x760 mm/page-writeback.c:2473
 mpage_writepages+0x72/0xe0 fs/mpage.c:679
 fat_writepages+0x24/0x30 fs/fat/inode.c:200
 do_writepages+0x1c5/0x340 mm/page-writeback.c:2551
 filemap_fdatawrite_wbc+0xdb/0xf0 mm/filemap.c:390
 __filemap_fdatawrite_range mm/filemap.c:423 [inline]
 filemap_write_and_wait_range+0xe6/0x220 mm/filemap.c:678
 generic_file_read_iter+0x103/0x320 mm/filemap.c:2811
 call_read_iter include/linux/fs.h:1862 [inline]
 aio_read+0x1df/0x2f0 fs/aio.c:1564
 io_submit_one+0xb74/0x12c0 fs/aio.c:2023
 __do_sys_io_submit fs/aio.c:2082 [inline]
 __se_sys_io_submit+0xf5/0x280 fs/aio.c:2052
 __x64_sys_io_submit+0x43/0x50 fs/aio.c:2052
 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

value changed: 0x0000000000241000 -> 0x0000000000242000

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 PID: 12852 Comm: syz-executor.5 Not tainted 6.4.0-rc7-syzkaller-00234-g547cc9be86f4 #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 05/27/2023
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