linux-kernel - Re: bpf selftest failed in 5.4.210 kernel

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Message-ID: <YwUdyiK16jz1W5Aa@myrica>
Date:   Tue, 23 Aug 2022 19:34:50 +0100
From:   Jean-Philippe Brucker <jean-philippe@...aro.org>
To:     RAJESH DASARI <raajeshdasari@...il.com>
Cc:     Greg KH <gregkh@...uxfoundation.org>, stable@...r.kernel.org,
        linux-kernel@...r.kernel.org, ovidiu.panait@...driver.com,
        alexei.starovoitov@...il.com, john.fastabend@...il.com
Subject: Re: bpf selftest failed in 5.4.210 kernel

On Tue, Aug 23, 2022 at 10:31:40AM +0300, RAJESH DASARI wrote:
> Sorry for the confusion, results are indeed confusing to me .
> If I try with git bisect I get
> 
> git bisect bad
> 9d6f67365d9cdb389fbdac2bb5b00e59e345930e is the first bad commit

For me bisecting points to:

(A)	7c1134c7da99 ("bpf: Verifer, adjust_scalar_min_max_vals to always call update_reg_bounds()")

This changes the BPF verifier output and (as expected) breaks the
test_align selftest. That's why in the same series [1] another patch fixed
test_align. In v5.4.y, that patch is:

(B)	6a9b3f0f3bad ("selftests/bpf: Fix test_align verifier log patterns")

Unfortunately commit (B) addresses multiple verifier changes, not solely
(A). My guess is those changes were in series [1] and haven't been
backported to v5.4. So multiple solutions:

* Partially revert (B), only keeping the changes needed by (A)
* Revert (A) and (B)
* Add the missing commits that (B) also addresses

I don't know which, I suppose it depends on the intent behind backporting
(A). Ovidiu?

In any case 6098562ed9df ("selftests/bpf: Fix "dubious pointer arithmetic"
test") can be reverted, I can send that once we figure out the rest.

Thanks,
Jean

[1] https://lore.kernel.org/bpf/158507130343.15666.8018068546764556975.stgit@john-Precision-5820-Tower/

> 
> If I  try to test myself with multiple test scenarios(I have mentioned
> in  the previous mails) for the bad commits , I see that bad commits
> are
> bpf: Verifer, adjust_scalar_min_max_vals to always call update_reg_bounds()
> selftests/bpf: Fix test_align verifier log patterns
> selftests/bpf: Fix "dubious pointer arithmetic" test
> 
> Thanks,
> Rajesh Dasari.
> 
> On Tue, Aug 23, 2022 at 10:04 AM Greg KH <gregkh@...uxfoundation.org> wrote:
> >
> > On Mon, Aug 22, 2022 at 10:23:02PM +0300, RAJESH DASARI wrote:
> > > Hi,
> > >
> > > Please find the test scenarios which I have tried.
> > >
> > > Test 1:
> > >
> > > Running system Kernel version (tag/commit) :  v5.4.210
> > > Kernel source code checkout : v5.4.210
> > > test_align test case execution status : Failure
> > >
> > > Test 2:
> > >
> > > Running system Kernel version (tag/commit) : v5.4.210
> > > Kernel source code checkout : v5.4.209
> > > test_align test case execution status : Failure
> > >
> > > Test 3:
> > >
> > > Running system Kernel version (tag/commit) : v5.4.209
> > > Kernel source code checkout : v5.4.209
> > > test_align test case execution status : Success
> > >
> > > Test 4:
> > >
> > > Running system Kernel version (tag/commit) : ACPI: APEI: Better fix to
> > > avoid spamming the console with old error logs ( Kernel compiled at
> > > this commit  and system is booted with this change)
> > > Kernel source code checkout : v5.4.210 but reverted selftests/bpf: Fix
> > > test_align verifier log patterns and selftests/bpf: Fix "dubious
> > > pointer arithmetic" test. If I revert only the Fix "dubious pointer
> > > arithmetic" test, the testcase still fails.
> > > test_align test case execution status : Success
> > >
> > > Test 5:
> > >
> > > Running system Kernel version (tag/commit) :  v5.4.210 but reverted
> > > commit (bpf: Verifer, adjust_scalar_min_max_vals to always call
> > > update_reg_bounds() )
> > > Kernel source code checkout : v5.4.210 but reverted selftests/bpf: Fix
> > > test_align verifier log patterns and selftests/bpf: Fix "dubious
> > > pointer arithmetic" test.
> > > test_align test case execution status : Success
> > >
> > > Test 6 :
> > >
> > > Running system Kernel version (tag/commit) : bpf: Test_verifier, #70
> > > error message updates for 32-bit right shift( Kernel compiled at this
> > > commit  and system is booted with this change)
> > > Kernel source code checkout : v5.4.209 or v5.4.210
> > > test_align test case execution status : Failure
> >
> > I'm sorry, but I don't know what to do with this report at all.
> >
> > Is there some failure somewhere?  If you use 'git bisect' do you find
> > the offending commit?
> >
> > confused,
> >
> > greg k-h