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Date:      Wed, 27 Nov 2019 18:57:21 +0000
From:      bugzilla-noreply@freebsd.org
To:        bugs@FreeBSD.org
Subject:   [Bug 242272] LinuxKPI combines all RCU and SRCU domains together, leading to deadlock
Message-ID:  <bug-242272-227@https.bugs.freebsd.org/bugzilla/>

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https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=3D242272

            Bug ID: 242272
           Summary: LinuxKPI combines all RCU and SRCU domains together,
                    leading to deadlock
           Product: Base System
           Version: CURRENT
          Hardware: Any
                OS: Any
            Status: New
          Severity: Affects Some People
          Priority: ---
         Component: kern
          Assignee: bugs@FreeBSD.org
          Reporter: aboyer@pensando.io

In that other OS, all RCU code is in the one domain, and each SRCU user gets
its own domain. (More or less.) They are all combined together in FreeBSD s=
ince
it has only a bare-bones implementation in the KPI.

This is a problem because ib_uverbs holds an SRCU read lock when calling in=
to
the provider's destroy_cq function. Providers may expect to be able to use =
RCU
primitives when tearing down, but calling synchronize_rcu() or
synchronize_srcu() will lead to a deadlock, even on a completely separate S=
RCU
domain.

To fix this will require adding real multiple-domain support to the KPI.

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