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BUG: KCSAN: data-race in ext4_ext_try_to_merge / ext4_mark_iloc_dirty

write to 0xffff88812878baf4 of 2 bytes by task 732 on cpu 0:
 ext4_ext_try_to_merge_up fs/ext4/extents.c:1826 [inline]
 ext4_ext_try_to_merge+0x2bf/0x360 fs/ext4/extents.c:1856
 ext4_convert_unwritten_extents_endio fs/ext4/extents.c:3868 [inline]
 ext4_ext_handle_unwritten_extents+0x29d/0x18f0 fs/ext4/extents.c:4048
 ext4_ext_map_blocks+0xa78/0x20f0 fs/ext4/extents.c:4318
 ext4_map_blocks+0x230/0xcf0 fs/ext4/inode.c:622
 ext4_convert_unwritten_extents+0x18b/0x3b0 fs/ext4/extents.c:4964
 ext4_convert_unwritten_io_end_vec+0xe0/0x1b0 fs/ext4/extents.c:4999
 ext4_end_io_end fs/ext4/page-io.c:189 [inline]
 ext4_do_flush_completed_IO fs/ext4/page-io.c:262 [inline]
 ext4_end_io_rsv_work+0x2c2/0x400 fs/ext4/page-io.c:276
 process_one_work+0x424/0x930 kernel/workqueue.c:2264
 worker_thread+0x9a/0x7e0 kernel/workqueue.c:2410
 kthread+0x1cb/0x1f0 kernel/kthread.c:255
 ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:352

read to 0xffff88812878baf4 of 4 bytes by task 5415 on cpu 1:
 ext4_do_update_inode fs/ext4/inode.c:4997 [inline]
 ext4_mark_iloc_dirty+0x9f0/0x1500 fs/ext4/inode.c:5578
 ext4_mark_inode_dirty+0xe6/0x420 fs/ext4/inode.c:5771
 ext4_dirty_inode+0xad/0xd0 fs/ext4/inode.c:5802
 __mark_inode_dirty+0x5b7/0x940 fs/fs-writeback.c:2258
 mark_inode_dirty include/linux/fs.h:2183 [inline]
 generic_write_end+0x1ba/0x1f0 fs/buffer.c:2199
 ext4_da_write_end+0x162/0x670 fs/ext4/inode.c:3092
 generic_perform_write+0x1d7/0x320 mm/filemap.c:3298
 ext4_buffered_write_iter+0x14e/0x280 fs/ext4/file.c:270
 ext4_file_write_iter+0xf4/0xd30 fs/ext4/file.c:642
 call_write_iter include/linux/fs.h:1901 [inline]
 new_sync_write+0x303/0x400 fs/read_write.c:483
 __vfs_write+0x9e/0xb0 fs/read_write.c:496
 vfs_write fs/read_write.c:558 [inline]
 vfs_write+0x189/0x380 fs/read_write.c:542
 ksys_write+0xc5/0x1a0 fs/read_write.c:611
 __do_sys_write fs/read_write.c:623 [inline]
 __se_sys_write fs/read_write.c:620 [inline]
 __x64_sys_write+0x49/0x60 fs/read_write.c:620
 do_syscall_64+0xc7/0x390 arch/x86/entry/common.c:294
 entry_SYSCALL_64_after_hwframe+0x44/0xa9

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 PID: 5415 Comm: syz-executor.2 Not tainted 5.6.0-rc1-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
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