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BUG: KCSAN: data-race in ext4_write_end / mpage_process_page_bufs

write to 0xffff88814b423bc8 of 8 bytes by task 3185 on cpu 1:
 i_size_write include/linux/fs.h:916 [inline]
 ext4_update_inode_size fs/ext4/ext4.h:3421 [inline]
 ext4_write_end+0x1be/0x800 fs/ext4/inode.c:1311
 ext4_da_write_end+0x93/0x730 fs/ext4/inode.c:3085
 generic_perform_write+0x251/0x3e0 mm/filemap.c:3781
 ext4_buffered_write_iter+0x309/0x400 fs/ext4/file.c:269
 ext4_file_write_iter+0x2f4/0x11f0
 call_write_iter include/linux/fs.h:2163 [inline]
 new_sync_write fs/read_write.c:507 [inline]
 vfs_write+0x79c/0x8d0 fs/read_write.c:594
 ksys_write+0xd9/0x190 fs/read_write.c:647
 __do_sys_write fs/read_write.c:659 [inline]
 __se_sys_write fs/read_write.c:656 [inline]
 __x64_sys_write+0x3e/0x50 fs/read_write.c:656
 do_syscall_x64 arch/x86/entry/common.c:50 [inline]
 do_syscall_64+0x44/0xa0 arch/x86/entry/common.c:80
 entry_SYSCALL_64_after_hwframe+0x44/0xae

read to 0xffff88814b423bc8 of 8 bytes by task 1153 on cpu 0:
 i_size_read include/linux/fs.h:894 [inline]
 mpage_process_page_bufs+0x34/0x560 fs/ext4/inode.c:2198
 mpage_prepare_extent_to_map+0x4f6/0x650 fs/ext4/inode.c:2632
 ext4_writepages+0xa18/0x1d70 fs/ext4/inode.c:2804
 do_writepages+0x26b/0x3c0 mm/page-writeback.c:2364
 __writeback_single_inode+0x80/0x440 fs/fs-writeback.c:1616
 writeback_sb_inodes+0x563/0xd30 fs/fs-writeback.c:1881
 wb_writeback+0x27d/0x6d0 fs/fs-writeback.c:2053
 wb_do_writeback+0x101/0x530 fs/fs-writeback.c:2196
 wb_workfn+0xc8/0x540 fs/fs-writeback.c:2237
 process_one_work+0x402/0x910 kernel/workqueue.c:2297
 worker_thread+0x636/0xae0 kernel/workqueue.c:2444
 kthread+0x262/0x280 kernel/kthread.c:319
 ret_from_fork+0x1f/0x30

value changed: 0x00000000000cb000 -> 0x00000000000cc000

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 PID: 1153 Comm: kworker/u4:8 Tainted: G        W         5.15.0-rc1-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
Workqueue: writeback wb_workfn (flush-8:0)
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