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BUG: KCSAN: data-race in fsnotify / fsnotify_recalc_mask

write to 0xffff88810d9ebe3c of 4 bytes by task 25432 on cpu 1:
 __fsnotify_recalc_mask fs/notify/mark.c:132 [inline]
 fsnotify_recalc_mask+0x17d/0x1e0 fs/notify/mark.c:147
 fsnotify_add_mark_locked+0x79b/0x970 fs/notify/mark.c:668
 fsnotify_add_inode_mark_locked include/linux/fsnotify_backend.h:543 [inline]
 inotify_new_watch fs/notify/inotify/inotify_user.c:597 [inline]
 inotify_update_watch fs/notify/inotify/inotify_user.c:624 [inline]
 __do_sys_inotify_add_watch fs/notify/inotify/inotify_user.c:762 [inline]
 __se_sys_inotify_add_watch+0x52a/0x660 fs/notify/inotify/inotify_user.c:705
 __x64_sys_inotify_add_watch+0x3f/0x50 fs/notify/inotify/inotify_user.c:705
 do_syscall_64+0x39/0x80 arch/x86/entry/common.c:46
 entry_SYSCALL_64_after_hwframe+0x44/0xae

read to 0xffff88810d9ebe3c of 4 bytes by task 25419 on cpu 0:
 fsnotify+0x181/0x1190 fs/notify/fsnotify.c:505
 __fsnotify_parent+0x3ac/0x430 fs/notify/fsnotify.c:232
 fsnotify_parent include/linux/fsnotify.h:68 [inline]
 fsnotify_file include/linux/fsnotify.h:90 [inline]
 fsnotify_modify include/linux/fsnotify.h:255 [inline]
 do_iter_write+0x432/0x4c0 fs/read_write.c:870
 vfs_iter_write+0x4c/0x70 fs/read_write.c:907
 iter_file_splice_write+0x40a/0x750 fs/splice.c:689
 do_splice_from fs/splice.c:767 [inline]
 direct_splice_actor+0x80/0xa0 fs/splice.c:936
 splice_direct_to_actor+0x345/0x650 fs/splice.c:891
 do_splice_direct+0xf5/0x170 fs/splice.c:979
 do_sendfile+0x7a6/0xe20 fs/read_write.c:1260
 __do_sys_sendfile64 fs/read_write.c:1319 [inline]
 __se_sys_sendfile64 fs/read_write.c:1311 [inline]
 __x64_sys_sendfile64+0xa9/0x130 fs/read_write.c:1311
 do_syscall_64+0x39/0x80 arch/x86/entry/common.c:46
 entry_SYSCALL_64_after_hwframe+0x44/0xae

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 PID: 25419 Comm: syz-executor.0 Not tainted 5.12.0-rc5-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
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