hwpmc: consistently validate PMC class in allocation method
ClosedPublic
Actions

Authored by mhorne on Aug 2 2021, 9:03 PM.

Details

Reviewers

luporl
ray
gnn

Group Reviewers

pmc

Commits

rG1e8f338d7f22: hwpmc: consistently validate PMC class in allocation method
rG315cd55dba61: hwpmc: consistently validate PMC class in allocation method

Summary

It is always a good idea. In one case, attempting to allocate N+1 PMCs
from a class with N hardware counters would incorrectly attempt to
allocate from the next class in the list. Without this validation, this
can lead to all kinds of unexpected behaviour.

Since powerpc_allocate_pmc() is used by both the mpc7xxx and ppc970
classes, add a new global to track which is active (it will never be
both).

Test Plan

On my desktop with 8 programmable counters, calling pmcstat with 9 separate events will panic the system. With this patch, it will fail to allocate the 9th, as expected.

Diff Detail

Repository

rS FreeBSD src repository - subversion

Lint

Lint Passed

Unit

No Test Coverage

Build Status

Buildable 40810
Build 37699: arc lint + arc unit

Event Timeline

mhorne created this revision.Aug 2 2021, 9:03 PM

Herald added a subscriber: imp. · View Herald TranscriptAug 2 2021, 9:03 PM

mhorne requested review of this revision.Aug 2 2021, 9:03 PM

Harbormaster completed remote builds in B40810: Diff 93139.Aug 2 2021, 9:04 PM

mhorne edited the test plan for this revision. (Show Details)Aug 2 2021, 9:06 PM

mhorne edited the test plan for this revision. (Show Details)

Ping.

ray accepted this revision as: ray.Aug 17 2021, 11:21 AM

This revision is now accepted and ready to land.Aug 17 2021, 11:21 AM

Worked fine on POWER9.
For PowerPC, without these changes the allocation of more programmable counters than available already failed, because of the check for the counter number in allocate. But, as you said, it is always a good idea to validate the PMC class too.

In D31387#713971, @luporl wrote:

Worked fine on POWER9.
For PowerPC, without these changes the allocation of more programmable counters than available already failed, because of the check for the counter number in allocate. But, as you said, it is always a good idea to validate the PMC class too.

That's right, the issue described only affects platforms which register more than one hwpmc class (where pcd->pcd_num != md->pmd_npmc).

Closed by commit rG315cd55dba61: hwpmc: consistently validate PMC class in allocation method (authored by mhorne). · Explain WhyAug 30 2021, 7:16 PM

This revision was automatically updated to reflect the committed changes.

mhorne added a commit: rG315cd55dba61: hwpmc: consistently validate PMC class in allocation method.

Herald added a reviewer: gnn. · View Herald TranscriptAug 30 2021, 7:16 PM

mav added a commit: rG1e8f338d7f22: hwpmc: consistently validate PMC class in allocation method.Jul 5 2022, 5:10 PM