[LTP] [PATCH] fs: exclude 'wakeup_count' from read_all_sys test.

[Richard Palethorpe <rpalethorpe@suse.de>]

Hello Sandeep,

Sandeep Patil <sspatil@google.com> writes:

> On Fri, Aug 10, 2018 at 04:10:04PM +0200, Richard Palethorpe wrote:
>> Hello,
>>
>> Sandeep Patil <sspatil@google.com> writes:
>>
>> > /sys/power/wakeup_count semantics state that the read() for the file
>> > will block as long as there is a wakeup_event in progress. On most
>> > systems, this will be non deterministic and will result in extremely
>> > flaky test. Exclude the file from read_all_sys test for the same.
>> >
>> > Signed-off-by: Sandeep Patil <sspatil@google.com>
>> > ---
>> >  runtest/fs | 2 +-
>> >  1 file changed, 1 insertion(+), 1 deletion(-)
>> >
>> > diff --git a/runtest/fs b/runtest/fs
>> > index a66948a43..aca7e355f 100644
>> > --- a/runtest/fs
>> > +++ b/runtest/fs
>> > @@ -71,7 +71,7 @@ proc01 proc01 -m 128
>> >
>> >  read_all_dev read_all -d /dev -p -q -r 10
>> >  read_all_proc read_all -d /proc -q -r 10
>> > -read_all_sys read_all -d /sys -q -r 10
>> > +read_all_sys read_all -d /sys -q -r 10 -e /sys/power/wakeup_count
>> >
>>
>> This probably won't be the only file with semantics like these. So I am
>> wondering if we can limit the time it spends blocking with timer_create
>> and SIGEV_THREAD_ID or something similar?
>
> Well, I actually like the fact that this test goes and reads everything and
> makes sure the kernel operations for those files are "sane". We ended up
> finding 2 different bugs due to this in the drivers, in 1 case it crashed the
> kernel and in the other the test halted forever until timeout.

This is good to know.

>
> So, unless the upstream ABI says the semantics are different for some files,
> I don't think we should do this. 'wakeup_count' is the one I found and after
> I exclude this, the test passes just fine on Pixel phones for example.
> (Including the debugfs mount point under /sys/kernel/debug).
>
> I say we wait for another case of exclusion show up before considering your
> approach as I think we will miss real problem if we start timing out. Plus,
> there is the question of whether we report the test as PASS / FAIL in those
> cases. The exclusion list is the right approach IMO. We may just have to
> figure out how to add more than one in the command line as they show up.
>
> Agree?
>

Yes, but possibly we should add a feature which allows us to annotate some
file's. Then we can mark this file as 'can_block', so if we do timeout
while reading it then we still know to PASS. Whereas for other files, we
can FAIL if it blocks. We discussed doing something like this
previously, but decided to wait for feedback before trying anything like
this. We already had to drop privileges due to /dev/watchdog, but
annotations could allow us to avoid this as well. This could perhaps go
into read_all02 and read_all01 just continues to use an exclude list and
drop privs.

I would be happy to implement said feature, but it may take a while. In
the meantime I'm not against merging this patch and waiting for another
file with similar problems to appear.

What do you think Metan? We could probably replace proc01 with
read_all02 as well.

> - ssp
>
>>
>> --
>> Thank you,
>> Richard.
>>
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--
Thank you,
Richard.