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BUG: KCSAN: data-race in __mpage_writepage / generic_write_end

write to 0xffff888124493728 of 8 bytes by task 8134 on cpu 1:
 i_size_write include/linux/fs.h:886 [inline]
 generic_write_end+0xb4/0x360 fs/buffer.c:2168
 fat_write_end+0x4e/0x160 fs/fat/inode.c:244
 generic_perform_write+0x253/0x3d0 mm/filemap.c:3783
 __generic_file_write_iter+0xe6/0x290 mm/filemap.c:3900
 generic_file_write_iter+0x7d/0x1c0 mm/filemap.c:3932
 do_iter_write+0x418/0x700 fs/read_write.c:861
 vfs_iter_write+0x50/0x70 fs/read_write.c:902
 iter_file_splice_write+0x42b/0x7b0 fs/splice.c:686
 do_splice_from fs/splice.c:764 [inline]
 direct_splice_actor+0x84/0xa0 fs/splice.c:931
 splice_direct_to_actor+0x2ee/0x5f0 fs/splice.c:886
 do_splice_direct+0x104/0x180 fs/splice.c:974
 do_sendfile+0x3b8/0x950 fs/read_write.c:1255
 __do_sys_sendfile64 fs/read_write.c:1323 [inline]
 __se_sys_sendfile64 fs/read_write.c:1309 [inline]
 __x64_sys_sendfile64+0x110/0x150 fs/read_write.c:1309
 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 0xffff888124493728 of 8 bytes by task 8138 on cpu 0:
 i_size_read include/linux/fs.h:864 [inline]
 __mpage_writepage+0xbf/0xd60 fs/mpage.c:469
 write_cache_pages+0x468/0xaa0 mm/page-writeback.c:2472
 mpage_writepages+0x72/0xe0 fs/mpage.c:664
 fat_writepages+0x24/0x30 fs/fat/inode.c:200
 do_writepages+0x1c7/0x330 mm/page-writeback.c:2581
 filemap_fdatawrite_wbc+0xdb/0xf0 mm/filemap.c:388
 __filemap_fdatawrite_range mm/filemap.c:421 [inline]
 filemap_write_and_wait_range+0xe6/0x220 mm/filemap.c:674
 generic_file_read_iter+0x103/0x320 mm/filemap.c:2808
 call_read_iter include/linux/fs.h:2183 [inline]
 generic_file_splice_read+0xe3/0x290 fs/splice.c:309
 do_splice_to fs/splice.c:793 [inline]
 splice_direct_to_actor+0x25a/0x5f0 fs/splice.c:865
 do_splice_direct+0x104/0x180 fs/splice.c:974
 do_sendfile+0x3b8/0x950 fs/read_write.c:1255
 __do_sys_sendfile64 fs/read_write.c:1323 [inline]
 __se_sys_sendfile64 fs/read_write.c:1309 [inline]
 __x64_sys_sendfile64+0x110/0x150 fs/read_write.c:1309
 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: 0x0000000000031e0c -> 0x0000000000032000

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 PID: 8138 Comm: syz-executor.3 Tainted: G        W          6.2.0-rc7-syzkaller-00018-g0983f6bf2bfc-dirty #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/21/2023
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