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BUG: KCSAN: data-race in ext4_setattr / ext4_writepages

write to 0xffff88812ca04748 of 8 bytes by task 26457 on cpu 0:
 i_size_write include/linux/fs.h:872 [inline]
 ext4_setattr+0xd54/0xec0 fs/ext4/inode.c:5483
 notify_change+0x8a3/0xa80 fs/attr.c:398
 do_truncate+0xe8/0x130 fs/open.c:64
 handle_truncate fs/namei.c:3020 [inline]
 do_open fs/namei.c:3371 [inline]
 path_openat+0x1a79/0x20b0 fs/namei.c:3500
 do_filp_open+0xd9/0x1f0 fs/namei.c:3527
 do_sys_openat2+0xa3/0x250 fs/open.c:1187
 do_sys_open fs/open.c:1203 [inline]
 __do_sys_creat fs/open.c:1277 [inline]
 __se_sys_creat fs/open.c:1271 [inline]
 __x64_sys_creat+0x62/0x80 fs/open.c:1271
 do_syscall_64+0x34/0x50 arch/x86/entry/common.c:46
 entry_SYSCALL_64_after_hwframe+0x44/0xae

read to 0xffff88812ca04748 of 8 bytes by task 26448 on cpu 1:
 i_size_read include/linux/fs.h:850 [inline]
 mpage_submit_page fs/ext4/inode.c:2096 [inline]
 mpage_map_and_submit_buffers fs/ext4/inode.c:2350 [inline]
 mpage_map_and_submit_extent fs/ext4/inode.c:2489 [inline]
 ext4_writepages+0x1008/0x1d10 fs/ext4/inode.c:2802
 do_writepages+0x7b/0x150 mm/page-writeback.c:2352
 __filemap_fdatawrite_range mm/filemap.c:424 [inline]
 __filemap_fdatawrite mm/filemap.c:432 [inline]
 filemap_flush+0x132/0x160 mm/filemap.c:459
 ext4_alloc_da_blocks+0x4a/0xd0 fs/ext4/inode.c:3166
 ext4_release_file+0x5b/0x1d0 fs/ext4/file.c:141
 __fput+0x25b/0x4e0 fs/file_table.c:280
 ____fput+0x11/0x20 fs/file_table.c:313
 task_work_run+0xae/0x130 kernel/task_work.c:140
 tracehook_notify_resume include/linux/tracehook.h:189 [inline]
 exit_to_user_mode_loop kernel/entry/common.c:174 [inline]
 exit_to_user_mode_prepare+0x151/0x170 kernel/entry/common.c:208
 __syscall_exit_to_user_mode_work kernel/entry/common.c:290 [inline]
 syscall_exit_to_user_mode+0x20/0x40 kernel/entry/common.c:301
 do_syscall_64+0x40/0x50 arch/x86/entry/common.c:56
 entry_SYSCALL_64_after_hwframe+0x44/0xae

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 PID: 26448 Comm: syz-executor.0 Not tainted 5.12.0-rc7-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
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