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closed by r310302 for knote(). If KN_INFLUX | KN_SCAN flags are set for the note passed to knote() or knote_fork(), i.e. the knote is scanned, we might erronously clear INFLUX when finishing notification. For normal knote() it was fixed in r310302 simply by remembering the fact that we do not own KN_INFLUX, since there we own knlist lock and scan thread cannot clear KN_INFLUX until we drop the lock. For knote_fork(), the situation is more complicated, e must drop knlist lock AKA the process lock, since we need to register new knotes. Change KN_INFLUX into counter and allow shared ownership of the in-flux state between scan and knote_fork() or knote(). Both in-flux setters need to ensure that knote is not dropped in parallel. Added assert about kn_influx == 1 in knote_drop() verifies that in-flux state is not shared when knote is destroyed. Since KBI of the struct knote is changed by addition of the int kn_influx field, reorder kn_hook and kn_hookid to fill pad on LP64 arches [1]. This keeps sizeof(struct knote) to same 128 bytes as it was before addition of kn_influx, on amd64. Reviewed by: markj Suggested by: markj [1] Tested by: pho (previous version) Sponsored by: The FreeBSD Foundation Differential revision: https://reviews.freebsd.org/D8898
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