Re: [RFC PATCH v2 10/10] selftets/damon/sysfs.py: pause DAMON before dumping status

SeongJae Park
2026-03-21T01:02:09Z

On Fri, 20 Mar 2026 08:41:33 -0700 SeongJae Park <sj@kernel.org> wrote:

> On Fri, 20 Mar 2026 08:29:39 -0700 SeongJae Park <sj@kernel.org> wrote:
>
> > Adding Sashiko comment
> > (https://lore.kernel.org/https://sashiko.dev/#/patchset/20260319052157.99433-11-sj@kernel.org)
> > with ': ' line prefix, and my replies in line.
> >
> > On Wed, 18 Mar 2026 22:21:53 -0700 SeongJae Park <sj@kernel.org> wrote:
> >
> > > The sysfs.py test commits DAMON parameters, dump the internal DAMON
> > > state, and show if the parameters are committed as expected using the
> > > dumped state. While the dumping is ongoing, DAMON is alive. It can
> > > make internal changes including addition and removal of regions. It can
> > > therefore make a race that can result in false test results. Pause
> > > DAMON execution during the state dumping to avoid such races.
> > >
> > > Signed-off-by: SeongJae Park <sj@kernel.org>
> > > ---
> > > tools/testing/selftests/damon/sysfs.py | 31 ++++++++++++++++++++++++++
> > > 1 file changed, 31 insertions(+)
> > >
> > > diff --git a/tools/testing/selftests/damon/sysfs.py b/tools/testing/selftests/damon/sysfs.py
> > > index e6d34ba05893f..704729c7a318e 100755
> > > --- a/tools/testing/selftests/damon/sysfs.py
> > > +++ b/tools/testing/selftests/damon/sysfs.py
> > > @@ -193,18 +193,48 @@ def assert_ctx_committed(ctx, dump):
> > > assert_true(dump['pause'] == ctx.pause, 'pause', dump)
> > >
> > > def assert_ctxs_committed(kdamonds):
> > > + ctxs_paused_for_dump = []
> > > + for kd in kdamonds.kdamonds:
> > > + for ctx in kd.contexts:
> > > + if ctx.pause is False:
> > > + ctx.pause = True
> > > + err = kd.commit()
> > > + if err is not None:
> > > + print('pause fail (%s)' % err)
> > > + kdamonds.stop()
> > > + exit(1)
> > > + ctxs_paused_for_dump.append(ctx)
> > > +
> > > status, err = dump_damon_status_dict(kdamonds.kdamonds[0].pid)
> > > if err is not None:
> > > print(err)
> > > kdamonds.stop()
> > > exit(1)
> > >
> > > + for kd in kdamonds.kdamonds:
> > > + for ctx in kd.contexts:
> > > + if ctx in ctxs_paused_for_dump:
> > > + ctx.pause = False
> > > + err = kd.commit()
> > > + if err is not None:
> > > + print('resume fail (%s)' % err)
> > > + kdamonds.stop()
> > > + exit(1)
> > > + # restore for comparison
> > > + ctx.pause = True
> >
> > : If a kdamond contains multiple contexts, does this loop leave earlier contexts
> > : paused in the kernel?
> > :
> > : Since kd.commit() stages and commits the state of all contexts associated with
> > : the kdamond, when kd.commit() is called for the second context, the first
> > : context's local pause attribute is already back to True.
> > :
> > : This would cause kd.commit() to write to sysfs and instruct the kernel to
> > : pause the first context again. By the end of this loop, only the last context
> > : in the kdamond would remain unpaused in the kernel.
> >
> > No. The pause field of the earlier context is set to False, so later
> > kd.commit() will commit the False 'pause' again. But this finds a good point.
> > There is no reason to call kd.commit() for each context. It is more efficient
> > to be called for each kdamond., thouth currently we support only one context
> > per kdamond. I will update the code so, in the next spin.
>
> I'm wrong, Sashiko is correct. I missed the last 'ctx.pause = True' in the
> loop. I will fix this together, like below:
>
> '''
> --- a/tools/testing/selftests/damon/sysfs.py
> +++ b/tools/testing/selftests/damon/sysfs.py
> @@ -201,16 +201,17 @@ def assert_ctx_committed(ctx, dump):
>
> def assert_ctxs_committed(kdamonds):
> ctxs_paused_for_dump = []
> + # pause for safe state dumping
> for kd in kdamonds.kdamonds:
> for ctx in kd.contexts:
> if ctx.pause is False:
> ctx.pause = True
> - err = kd.commit()
> - if err is not None:
> - print('pause fail (%s)' % err)
> - kdamonds.stop()
> - exit(1)
> ctxs_paused_for_dump.append(ctx)
> + err = kd.commit()
> + if err is not None:
> + print('pause fail (%s)' % err)
> + kdamonds.stop()
> + exit(1)
>
> status, err = dump_damon_status_dict(kdamonds.kdamonds[0].pid)
> if err is not None:
> @@ -218,17 +219,19 @@ def assert_ctxs_committed(kdamonds):
> kdamonds.stop()
> exit(1)
>
> + # resume contexts paused for safe state dumping
> for kd in kdamonds.kdamonds:
> - for ctx in kd.contexts:
> - if ctx in ctxs_paused_for_dump:
> - ctx.pause = False
> - err = kd.commit()
> - if err is not None:
> - print('resume fail (%s)' % err)
> - kdamonds.stop()
> - exit(1)
> - # restore for comparison
> - ctx.pause = True
> + for ctx in ctxs_paused_for_dump:
> + ctx.pause = False
> + err = kd.commit()
> + if err is not None:
> + print('resume fail (%s)' % err)
> + kdamonds.stop()
> + exit(1)
> +
> + # restore for comparison
> + for ctx in ctxs_paused_for_dump:
> + ctx.pause = True
>
> ctxs = kdamonds.kdamonds[0].contexts
> dump = status['contexts']
> '''

The above fixup makes the test fails, for the obsolete targets. The fixup
needs another fixup, like below. I will add that to the next spin.

'''
--- a/tools/testing/selftests/damon/sysfs.py
+++ b/tools/testing/selftests/damon/sysfs.py
@@ -200,11 +200,12 @@ def assert_ctxs_committed(kdamonds):
if ctx.pause is False:
ctx.pause = True
ctxs_paused_for_dump.append(ctx)
- err = kd.commit()
- if err is not None:
- print('pause fail (%s)' % err)
- kdamonds.stop()
- exit(1)
+ if len(ctxs_paused_for_dump) > 0:
+ err = kd.commit()
+ if err is not None:
+ print('pause fail (%s)' % err)
+ kdamonds.stop()
+ exit(1)

status, err = dump_damon_status_dict(kdamonds.kdamonds[0].pid)
if err is not None:
@@ -216,11 +217,12 @@ def assert_ctxs_committed(kdamonds):
for kd in kdamonds.kdamonds:
for ctx in ctxs_paused_for_dump:
ctx.pause = False
- err = kd.commit()
- if err is not None:
- print('resume fail (%s)' % err)
- kdamonds.stop()
- exit(1)
+ if len(ctxs_paused_for_dump) > 0:
+ err = kd.commit()
+ if err is not None:
+ print('resume fail (%s)' % err)
+ kdamonds.stop()
+ exit(1)

# restore for comparison
for ctx in ctxs_paused_for_dump:
'''

Thanks,
SJ