==================================================================
BUG: KCSAN: data-race in __xa_set_mark / ext4_writepages

write to 0xffff88813081f3f4 of 4 bytes by task 2243 on cpu 1:
 xa_mark_set lib/xarray.c:69 [inline]
 xas_set_mark lib/xarray.c:889 [inline]
 __xa_set_mark+0x279/0x290 lib/xarray.c:1899
 __set_page_dirty+0x155/0x1a0 fs/buffer.c:609
 mark_buffer_dirty+0x126/0x200 fs/buffer.c:1137
 __block_commit_write fs/buffer.c:2084 [inline]
 block_write_end+0x13d/0x260 fs/buffer.c:2163
 ext4_write_end+0x192/0x820 fs/ext4/inode.c:1301
 ext4_da_write_end+0x93/0x730 fs/ext4/inode.c:3081
 generic_perform_write+0x23e/0x3a0 mm/filemap.c:3593
 ext4_buffered_write_iter+0x2f2/0x3f0 fs/ext4/file.c:269
 ext4_file_write_iter+0x2e7/0x11d0 fs/ext4/file.c:502
 call_write_iter include/linux/fs.h:1977 [inline]
 aio_write+0x287/0x360 fs/aio.c:1581
 __io_submit_one fs/aio.c:1840 [inline]
 io_submit_one+0x82f/0x1350 fs/aio.c:1883
 __do_sys_io_submit fs/aio.c:1942 [inline]
 __se_sys_io_submit+0xf5/0x260 fs/aio.c:1912
 __x64_sys_io_submit+0x3f/0x50 fs/aio.c:1912
 do_syscall_64+0x34/0x50 arch/x86/entry/common.c:46
 entry_SYSCALL_64_after_hwframe+0x44/0xae

read to 0xffff88813081f3f4 of 4 bytes by task 15250 on cpu 0:
 xa_marked include/linux/xarray.h:418 [inline]
 mapping_tagged include/linux/fs.h:490 [inline]
 ext4_writepages+0x130/0x1d10 fs/ext4/inode.c:2670
 do_writepages+0x7b/0x150 mm/page-writeback.c:2352
 __writeback_single_inode+0x80/0x450 fs/fs-writeback.c:1467
 writeback_sb_inodes+0x564/0xf10 fs/fs-writeback.c:1732
 wb_writeback+0x28e/0x700 fs/fs-writeback.c:1905
 wb_do_writeback+0x101/0x510 fs/fs-writeback.c:2050
 wb_workfn+0xc8/0x520 fs/fs-writeback.c:2091
 process_one_work+0x3e9/0x8f0 kernel/workqueue.c:2275
 process_scheduled_works kernel/workqueue.c:2337 [inline]
 worker_thread+0x7ff/0xae0 kernel/workqueue.c:2423
 kthread+0x1d0/0x1f0 kernel/kthread.c:292
 ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:294

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 PID: 15250 Comm: kworker/u4:7 Not tainted 5.12.0-rc8-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
Workqueue: writeback wb_workfn (flush-8:0)
==================================================================
EXT4-fs (sda1): Delayed block allocation failed for inode 16381 at logical offset 511 with max blocks 2 with error 28
EXT4-fs (sda1): This should not happen!! Data will be lost

EXT4-fs: 30 callbacks suppressed
EXT4-fs (sda1): Delayed block allocation failed for inode 15221 at logical offset 7 with max blocks 1 with error 28
EXT4-fs (sda1): This should not happen!! Data will be lost

EXT4-fs (sda1): Total free blocks count 0
EXT4-fs (sda1): Free/Dirty block details
EXT4-fs (sda1): free_blocks=11040
EXT4-fs (sda1): dirty_blocks=5526
EXT4-fs (sda1): Block reservation details
EXT4-fs (sda1): i_reserved_data_blocks=1
EXT4-fs (sda1): Delayed block allocation failed for inode 15350 at logical offset 64 with max blocks 127 with error 28
EXT4-fs (sda1): This should not happen!! Data will be lost