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BUG: KCSAN: data-race in ext4_da_write_end / ext4_writepages

write to 0xffff88810636bbc8 of 8 bytes by task 1860 on cpu 0:
 mpage_map_and_submit_extent fs/ext4/inode.c:2513 [inline]
 ext4_writepages+0x13da/0x1d30 fs/ext4/inode.c:2806
 do_writepages+0x25b/0x3a0 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+0x25d/0x6b0 fs/fs-writeback.c:2053
 wb_do_writeback+0x101/0x510 fs/fs-writeback.c:2196
 wb_workfn+0xc8/0x520 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

read to 0xffff88810636bbc8 of 8 bytes by task 18023 on cpu 1:
 ext4_da_write_end+0xfc/0x730 fs/ext4/inode.c:3098
 generic_perform_write+0x23a/0x3d0 mm/filemap.c:3781
 ext4_buffered_write_iter+0x305/0x400 fs/ext4/file.c:269
 ext4_file_write_iter+0x2e7/0x11a0
 call_write_iter include/linux/fs.h:2163 [inline]
 new_sync_write fs/read_write.c:507 [inline]
 vfs_write+0x77d/0x8c0 fs/read_write.c:594
 ksys_write+0xce/0x180 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+0x3d/0x90 arch/x86/entry/common.c:80
 entry_SYSCALL_64_after_hwframe+0x44/0xae

value changed: 0x0000000000040000 -> 0x00000000001d6000

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 PID: 18023 Comm: syz-executor.5 Not tainted 5.14.0-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
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