[PATCHSET sched_ext/for-7.3-fixes] sched_ext: Fix bypass propagation and the bypass dispatch claim for overlapping bypasses

[Tejun Heo]

Hello,

scx_bypass() propagates a bypass to the descendants, and claims bypass
dispatch on the host, only when the scheduler's own depth crosses zero. A
sub-scheduler's own bypass that overlaps an ancestor's then misses both: its
descendants drop out of bypass early, and its claim is leaked or never
taken. A PM suspend over a sub-scheduler's enable trips the WARN_ON_ONCE()
in enable_bypass_dsp() on the next bypass, and one over a disable leaves its
tasks on the parent's bypass DSQs with nobody consuming them.

Patch 1 propagates every depth change so that a descendant's depth is the
sum of its own and its ancestors' bypasses. Patch 2 claims and releases
bypass dispatch for the propagated descendants too.

Verified with a debug patch holding a sub-scheduler's enable bypass open
across PM suspend cycles: every suspend landed inside it, the unfixed kernel
trips the WARN on the following disable and the fixed one does not, with the
sub-scheduler's tasks running after each resume. The claim protocol across
the PM notifier, sub-scheduler enable and disable and root disable was
model-checked with TLC, including the sequences fixed here.

Based on sched_ext/for-7.3-fixes (069403dff337).

This patchset contains the following 2 patches.

 0001 sched_ext: Propagate every bypass depth change to the descendants
 0002 sched_ext: Fix the bypass dispatch claim for schedulers bypassed by an ancestor

The patchset is also available in the following git branch:

 git://git.kernel.org/pub/scm/linux/kernel/git/tj/sched_ext.git bypass-claim-fixes

diffstat follows. Thanks.

 kernel/sched/ext/ext.c | 54 ++++++++++++++++++++++++++++++--------------------
 1 file changed, 33 insertions(+), 21 deletions(-)

--
tejun