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BUG: KCSAN: data-race in generic_write_end / mpage_process_page_bufs

write to 0xffff88810a095848 of 8 bytes by task 3598 on cpu 1:
 i_size_write include/linux/fs.h:932 [inline]
 generic_write_end+0x94/0x230 fs/buffer.c:2280
 ext4_da_write_end+0x49e/0x6f0 fs/ext4/inode.c:2988
 generic_perform_write+0x267/0x410 mm/filemap.c:3956
 ext4_buffered_write_iter+0x1f6/0x370 fs/ext4/file.c:299
 ext4_file_write_iter+0x283/0x1230
 call_write_iter include/linux/fs.h:1985 [inline]
 new_sync_write fs/read_write.c:491 [inline]
 vfs_write+0x4ab/0x7d0 fs/read_write.c:584
 ksys_write+0xeb/0x1a0 fs/read_write.c:637
 __do_sys_write fs/read_write.c:649 [inline]
 __se_sys_write fs/read_write.c:646 [inline]
 __x64_sys_write+0x42/0x50 fs/read_write.c:646
 do_syscall_x64 arch/x86/entry/common.c:50 [inline]
 do_syscall_64+0x41/0xc0 arch/x86/entry/common.c:80
 entry_SYSCALL_64_after_hwframe+0x63/0xcd

read to 0xffff88810a095848 of 8 bytes by task 3235 on cpu 0:
 i_size_read include/linux/fs.h:910 [inline]
 mpage_process_page_bufs+0x34/0x5d0 fs/ext4/inode.c:1956
 mpage_prepare_extent_to_map+0x780/0xb70 fs/ext4/inode.c:2487
 ext4_do_writepages+0xa52/0x21c0 fs/ext4/inode.c:2675
 ext4_writepages+0x15e/0x2e0 fs/ext4/inode.c:2766
 do_writepages+0x1c2/0x340 mm/page-writeback.c:2553
 __writeback_single_inode+0x91/0x860 fs/fs-writeback.c:1603
 writeback_sb_inodes+0x511/0xaa0 fs/fs-writeback.c:1894
 wb_writeback+0x252/0x6e0 fs/fs-writeback.c:2070
 wb_do_writeback fs/fs-writeback.c:2217 [inline]
 wb_workfn+0x1a8/0x8d0 fs/fs-writeback.c:2257
 process_one_work+0x434/0x860 kernel/workqueue.c:2600
 worker_thread+0x5f2/0xa10 kernel/workqueue.c:2751
 kthread+0x1d7/0x210 kernel/kthread.c:388
 ret_from_fork+0x48/0x60 arch/x86/kernel/process.c:145
 ret_from_fork_asm+0x11/0x20 arch/x86/entry/entry_64.S:304

value changed: 0x0000000000b03000 -> 0x0000000000b04000

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 PID: 3235 Comm: kworker/u4:6 Not tainted 6.5.0-syzkaller-08262-gef2a0b7cdbc5 #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 07/26/2023
Workqueue: writeback wb_workfn (flush-8:0)
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