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BUG: KCSAN: data-race in ext4_setattr / mpage_process_page_bufs

write to 0xffff888128c81830 of 8 bytes by task 18811 on cpu 1:
 i_size_write include/linux/fs.h:888 [inline]
 ext4_setattr+0xd58/0x1290 fs/ext4/inode.c:5340
 notify_change+0x82b/0xb00 fs/attr.c:336
 do_truncate+0xf9/0x180 fs/open.c:64
 handle_truncate fs/namei.c:3083 [inline]
 do_last fs/namei.c:3496 [inline]
 path_openat+0x1241/0x2f70 fs/namei.c:3607
 do_filp_open+0x11e/0x1b0 fs/namei.c:3637
 do_sys_openat2+0x4f5/0x620 fs/open.c:1149
 do_sys_open+0xa2/0x110 fs/open.c:1165
 __do_sys_openat fs/open.c:1179 [inline]
 __se_sys_openat fs/open.c:1174 [inline]
 __x64_sys_openat+0x5d/0x70 fs/open.c:1174
 do_syscall_64+0xc7/0x390 arch/x86/entry/common.c:294
 entry_SYSCALL_64_after_hwframe+0x44/0xa9

read to 0xffff888128c81830 of 8 bytes by task 18808 on cpu 0:
 mpage_process_page_bufs+0x3f/0x400 fs/ext4/inode.c:2166
 mpage_prepare_extent_to_map+0x43b/0x6e0 fs/ext4/inode.c:2597
 ext4_writepages+0xb00/0x1d40 fs/ext4/inode.c:2769
 do_writepages+0x6b/0x170 mm/page-writeback.c:2344
 __filemap_fdatawrite_range+0x1bb/0x220 mm/filemap.c:421
 __filemap_fdatawrite mm/filemap.c:429 [inline]
 filemap_flush+0x2a/0x40 mm/filemap.c:456
 ext4_alloc_da_blocks+0x72/0x170 fs/ext4/inode.c:3146
 ext4_release_file+0x107/0x200 fs/ext4/file.c:142
 __fput+0x1c3/0x4f0 fs/file_table.c:280
 ____fput+0x1b/0x30 fs/file_table.c:313
 task_work_run+0xf5/0x130 kernel/task_work.c:113
 tracehook_notify_resume include/linux/tracehook.h:188 [inline]
 exit_to_usermode_loop+0x2ae/0x2c0 arch/x86/entry/common.c:164
 prepare_exit_to_usermode arch/x86/entry/common.c:195 [inline]
 syscall_return_slowpath arch/x86/entry/common.c:278 [inline]
 do_syscall_64+0x36e/0x390 arch/x86/entry/common.c:304
 entry_SYSCALL_64_after_hwframe+0x44/0xa9

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 PID: 18808 Comm: syz-executor.5 Not tainted 5.6.0-rc1-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
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