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BUG: KCSAN: data-race in __mpage_writepage / generic_write_end

write to 0xffff8881341a23f8 of 8 bytes by task 27208 on cpu 1:
 i_size_write include/linux/fs.h:907 [inline]
 generic_write_end+0x96/0x180 fs/buffer.c:2187
 fat_write_end+0x4a/0x160 fs/fat/inode.c:249
 generic_perform_write+0x261/0x400 mm/filemap.c:3776
 __generic_file_write_iter+0xf7/0x2b0 mm/filemap.c:3892
 generic_file_write_iter+0x75/0x130 mm/filemap.c:3924
 call_write_iter include/linux/fs.h:2074 [inline]
 do_iter_readv_writev+0x2de/0x380 fs/read_write.c:725
 do_iter_write+0x192/0x5c0 fs/read_write.c:851
 vfs_iter_write+0x4c/0x70 fs/read_write.c:892
 iter_file_splice_write+0x43a/0x790 fs/splice.c:689
 do_splice_from fs/splice.c:767 [inline]
 direct_splice_actor+0x80/0xa0 fs/splice.c:936
 splice_direct_to_actor+0x345/0x650 fs/splice.c:891
 do_splice_direct+0x106/0x190 fs/splice.c:979
 do_sendfile+0x675/0xc40 fs/read_write.c:1245
 __do_sys_sendfile64 fs/read_write.c:1310 [inline]
 __se_sys_sendfile64 fs/read_write.c:1296 [inline]
 __x64_sys_sendfile64+0x102/0x140 fs/read_write.c:1296
 do_syscall_x64 arch/x86/entry/common.c:50 [inline]
 do_syscall_64+0x44/0xd0 arch/x86/entry/common.c:80
 entry_SYSCALL_64_after_hwframe+0x44/0xae

read to 0xffff8881341a23f8 of 8 bytes by task 27213 on cpu 0:
 i_size_read include/linux/fs.h:885 [inline]
 __mpage_writepage+0xbe/0x1060 fs/mpage.c:492
 write_cache_pages+0x454/0x7f0 mm/page-writeback.c:2255
 mpage_writepages+0x7f/0x130 fs/mpage.c:705
 fat_writepages+0x20/0x30 fs/fat/inode.c:205
 do_writepages+0x1cb/0x330 mm/page-writeback.c:2364
 filemap_fdatawrite_wbc mm/filemap.c:384 [inline]
 __filemap_fdatawrite_range mm/filemap.c:417 [inline]
 file_write_and_wait_range+0x134/0x1d0 mm/filemap.c:775
 __generic_file_fsync+0x48/0x140 fs/libfs.c:1115
 fat_file_fsync+0x48/0x100 fs/fat/file.c:191
 vfs_fsync_range+0x107/0x120 fs/sync.c:188
 generic_write_sync include/linux/fs.h:2884 [inline]
 generic_file_write_iter+0x103/0x130 mm/filemap.c:3928
 call_write_iter include/linux/fs.h:2074 [inline]
 do_iter_readv_writev+0x2de/0x380 fs/read_write.c:725
 do_iter_write+0x192/0x5c0 fs/read_write.c:851
 vfs_iter_write+0x4c/0x70 fs/read_write.c:892
 iter_file_splice_write+0x43a/0x790 fs/splice.c:689
 do_splice_from fs/splice.c:767 [inline]
 direct_splice_actor+0x80/0xa0 fs/splice.c:936
 splice_direct_to_actor+0x345/0x650 fs/splice.c:891
 do_splice_direct+0x106/0x190 fs/splice.c:979
 do_sendfile+0x675/0xc40 fs/read_write.c:1245
 __do_sys_sendfile64 fs/read_write.c:1304 [inline]
 __se_sys_sendfile64 fs/read_write.c:1296 [inline]
 __x64_sys_sendfile64+0xb9/0x140 fs/read_write.c:1296
 do_syscall_x64 arch/x86/entry/common.c:50 [inline]
 do_syscall_64+0x44/0xd0 arch/x86/entry/common.c:80
 entry_SYSCALL_64_after_hwframe+0x44/0xae

value changed: 0x000000000017f000 -> 0x0000000000180000

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 PID: 27213 Comm: syz-executor.2 Not tainted 5.17.0-rc7-syzkaller-00205-g79b00034e9dc-dirty #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
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