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BUG: KCSAN: data-race in ext4_writepages / generic_write_end

write to 0xffff888119d152a8 of 8 bytes by task 6362 on cpu 0:
 i_size_write include/linux/fs.h:907 [inline]
 generic_write_end+0x96/0x180 fs/buffer.c:2187
 ext4_da_write_end+0x4de/0x630 fs/ext4/inode.c:3042
 generic_perform_write+0x261/0x400 mm/filemap.c:3776
 ext4_buffered_write_iter+0x244/0x360 fs/ext4/file.c:268
 ext4_file_write_iter+0x2e7/0x11f0
 call_write_iter include/linux/fs.h:2074 [inline]
 new_sync_write fs/read_write.c:503 [inline]
 vfs_write+0x7f5/0x950 fs/read_write.c:590
 ksys_write+0xd9/0x190 fs/read_write.c:643
 __do_sys_write fs/read_write.c:655 [inline]
 __se_sys_write fs/read_write.c:652 [inline]
 __x64_sys_write+0x3e/0x50 fs/read_write.c:652
 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 0xffff888119d152a8 of 8 bytes by task 6376 on cpu 1:
 i_size_read include/linux/fs.h:885 [inline]
 mpage_submit_page fs/ext4/inode.c:2074 [inline]
 mpage_map_and_submit_buffers fs/ext4/inode.c:2326 [inline]
 mpage_map_and_submit_extent fs/ext4/inode.c:2465 [inline]
 ext4_writepages+0x10b6/0x1e80 fs/ext4/inode.c:2778
 do_writepages+0x1cb/0x330 mm/page-writeback.c:2364
 filemap_fdatawrite_wbc mm/filemap.c:384 [inline]
 __filemap_fdatawrite_range+0xe1/0x110 mm/filemap.c:417
 generic_fadvise+0x1dc/0x430 mm/fadvise.c:113
 vfs_fadvise mm/fadvise.c:186 [inline]
 ksys_fadvise64_64 mm/fadvise.c:200 [inline]
 __do_sys_fadvise64 mm/fadvise.c:215 [inline]
 __se_sys_fadvise64 mm/fadvise.c:213 [inline]
 __x64_sys_fadvise64+0xc5/0x100 mm/fadvise.c:213
 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: 0x0000000000a73000 -> 0x0000000000a74000

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 PID: 6376 Comm: syz-executor.3 Not tainted 5.17.0-rc2-syzkaller-00064-gc36c04c2e132 #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
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