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BUG: KCSAN: data-race in mm_update_next_owner / stop_this_handle

write to 0xffff88810973f02c of 4 bytes by task 8447 on cpu 1:
 memalloc_nofs_restore include/linux/sched/mm.h:258 [inline]
 stop_this_handle+0x2ae/0x2f0 fs/jbd2/transaction.c:744
 jbd2_journal_stop+0x573/0x6d0 fs/jbd2/transaction.c:1907
 __ext4_journal_stop+0x99/0x110 fs/ext4/ext4_jbd2.c:127
 ext4_dirty_inode+0xba/0xc0 fs/ext4/inode.c:5957
 __mark_inode_dirty+0x72/0x6b0 fs/fs-writeback.c:2262
 generic_update_time fs/inode.c:1763 [inline]
 update_time fs/inode.c:1776 [inline]
 touch_atime+0x1b1/0x2d0 fs/inode.c:1847
 pick_link fs/namei.c:1637 [inline]
 step_into+0x83c/0xeb0 fs/namei.c:1717
 walk_component+0x190/0x350 fs/namei.c:1867
 lookup_last fs/namei.c:2312 [inline]
 path_lookupat+0x12d/0x560 fs/namei.c:2336
 filename_lookup+0xf2/0x380 fs/namei.c:2369
 user_path_at_empty+0x3b/0x50 fs/namei.c:2649
 user_path_at include/linux/namei.h:59 [inline]
 ksys_umount fs/namespace.c:1757 [inline]
 __do_sys_umount fs/namespace.c:1765 [inline]
 __se_sys_umount fs/namespace.c:1763 [inline]
 __x64_sys_umount+0x75/0xd0 fs/namespace.c:1763
 do_syscall_64+0x39/0x80 arch/x86/entry/common.c:46
 entry_SYSCALL_64_after_hwframe+0x44/0xa9

read to 0xffff88810973f02c of 4 bytes by task 19228 on cpu 0:
 mm_update_next_owner+0x1d9/0x4e0 kernel/exit.c:388
 exit_mm+0x337/0x430 kernel/exit.c:500
 do_exit+0x41f/0x1690 kernel/exit.c:812
 do_group_exit+0x17d/0x180 kernel/exit.c:922
 __do_sys_exit_group+0xb/0x10 kernel/exit.c:933
 __se_sys_exit_group+0x5/0x10 kernel/exit.c:931
 __x64_sys_exit_group+0x16/0x20 kernel/exit.c:931
 do_syscall_64+0x39/0x80 arch/x86/entry/common.c:46
 entry_SYSCALL_64_after_hwframe+0x44/0xa9

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 PID: 19228 Comm: syz-executor.1 Not tainted 5.11.0-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
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