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PP mutexes: lock: Check if priority is too high against base one

Description

PP mutexes: lock: Check if priority is too high against base one

Doing this instead of using the current (user) priority, which includes
current lendings, prevents gratuitous failures for threads involved in
multiple locking groups, where each group is defined as the threads that
can lock a particular PP or PI mutex. No deadlock can occur in this
case. Indeed, if a thread holds such a lock A giving it a higher
priority than the ceiling of some other lock B that is PP, and B is
acquired by another thread, effectively the latter may not be able to
run but this situation can only last until the first thread releases A,
which it will do eventually.

Reviewed by: kib
Approved by: emaste (mentor)
MFC after: 2 weeks
Sponsored by: The FreeBSD Foundation
Differential Revision: https://reviews.freebsd.org/D44044

(cherry picked from commit 9ac3ac9ece6269365ac314fa5fdb484e96d4a32e)

Approved by: emaste (mentor)

Details

Provenance
olceAuthored on Feb 22 2024, 8:53 AM
Reviewer
kib
Differential Revision
D44044: PP mutexes: lock: Check if priority is too high against base one
Parents
rGeded8fea5c3a: PP mutexes: unlock: Reset inherited prio regardless of privileges
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