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BUG: KCSAN: data-race in ext4_write_end / mpage_process_page_bufs

write to 0xffff888106a2f210 of 8 bytes by task 13849 on cpu 0:
 i_size_write include/linux/fs.h:871 [inline]
 ext4_update_inode_size fs/ext4/ext4.h:3359 [inline]
 ext4_write_end+0x1d7/0x820 fs/ext4/inode.c:1309
 generic_perform_write+0x22a/0x3c0 mm/filemap.c:3667
 ext4_buffered_write_iter+0x2f2/0x3f0 fs/ext4/file.c:269
 ext4_file_write_iter+0x2e7/0x11d0 fs/ext4/file.c:519
 call_write_iter include/linux/fs.h:2114 [inline]
 new_sync_write fs/read_write.c:518 [inline]
 vfs_write+0x69d/0x770 fs/read_write.c:605
 ksys_write+0xce/0x180 fs/read_write.c:658
 __do_sys_write fs/read_write.c:670 [inline]
 __se_sys_write fs/read_write.c:667 [inline]
 __x64_sys_write+0x3e/0x50 fs/read_write.c:667
 do_syscall_x64 arch/x86/entry/common.c:50 [inline]
 do_syscall_64+0x3d/0x90 arch/x86/entry/common.c:80
 entry_SYSCALL_64_after_hwframe+0x44/0xae

read to 0xffff888106a2f210 of 8 bytes by task 13856 on cpu 1:
 i_size_read include/linux/fs.h:849 [inline]
 mpage_process_page_bufs+0x34/0x560 fs/ext4/inode.c:2192
 mpage_prepare_extent_to_map+0x4e6/0x640 fs/ext4/inode.c:2626
 ext4_writepages+0x6c6/0x1d10 fs/ext4/inode.c:2754
 do_writepages+0x7b/0x150 mm/page-writeback.c:2355
 __filemap_fdatawrite_range mm/filemap.c:413 [inline]
 filemap_write_and_wait_range+0x20a/0x390 mm/filemap.c:686
 filemap_write_and_wait include/linux/fs.h:2897 [inline]
 iomap_bmap+0x68/0x110 fs/iomap/fiemap.c:130
 ext4_bmap+0x213/0x230 fs/ext4/inode.c:3233
 bmap+0x56/0x80 fs/inode.c:1711
 ioctl_fibmap fs/ioctl.c:77 [inline]
 file_ioctl fs/ioctl.c:534 [inline]
 do_vfs_ioctl+0x1284/0x1410 fs/ioctl.c:1048
 __do_sys_ioctl fs/ioctl.c:1067 [inline]
 __se_sys_ioctl+0x83/0x140 fs/ioctl.c:1055
 __x64_sys_ioctl+0x3f/0x50 fs/ioctl.c:1055
 do_syscall_x64 arch/x86/entry/common.c:50 [inline]
 do_syscall_64+0x3d/0x90 arch/x86/entry/common.c:80
 entry_SYSCALL_64_after_hwframe+0x44/0xae

value changed: 0x0000000000107000 -> 0x0000000000108000

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 PID: 13856 Comm: syz-executor.5 Not tainted 5.14.0-rc7-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
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