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BUG: KCSAN: data-race in ext4_da_write_end / ext4_writepages

write to 0xffff88813a0ef6d8 of 8 bytes by task 26302 on cpu 0:
 mpage_map_and_submit_extent fs/ext4/inode.c:2507 [inline]
 ext4_writepages+0x13ca/0x1d10 fs/ext4/inode.c:2800
 do_writepages+0x7b/0x150 mm/page-writeback.c:2355
 __filemap_fdatawrite_range mm/filemap.c:413 [inline]
 file_write_and_wait_range+0x180/0x210 mm/filemap.c:792
 ext4_sync_file+0x105/0x670 fs/ext4/fsync.c:151
 vfs_fsync_range fs/sync.c:200 [inline]
 vfs_fsync fs/sync.c:214 [inline]
 do_fsync fs/sync.c:224 [inline]
 __do_sys_fdatasync fs/sync.c:237 [inline]
 __se_sys_fdatasync fs/sync.c:235 [inline]
 __x64_sys_fdatasync+0x7a/0xd0 fs/sync.c:235
 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 0xffff88813a0ef6d8 of 8 bytes by task 26307 on cpu 1:
 ext4_da_write_end+0xfc/0x730 fs/ext4/inode.c:3092
 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

value changed: 0x0000000000400000 -> 0x00000000006d0000

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 PID: 26307 Comm: syz-executor.3 Not tainted 5.14.0-rc1-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
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