linux-kernel - Re: [RFC PATCH 2/6] testing/pkeys: Don't use uninitialized variable

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Message-ID: <YqfPV3AGo6ZWCsr7@iweiny-desk3>
Date:   Mon, 13 Jun 2022 16:59:19 -0700
From:   Ira Weiny <ira.weiny@...el.com>
To:     Sohil Mehta <sohil.mehta@...el.com>
CC:     <linux-api@...r.kernel.org>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        "Aneesh Kumar K . V" <aneesh.kumar@...ux.ibm.com>,
        <x86@...nel.org>, <linuxppc-dev@...ts.ozlabs.org>,
        <linux-kernel@...r.kernel.org>, <linux-mm@...ck.org>,
        <linux-kselftest@...r.kernel.org>
Subject: Re: [RFC PATCH 2/6] testing/pkeys: Don't use uninitialized variable

On Mon, Jun 13, 2022 at 03:48:56PM -0700, Mehta, Sohil wrote:
> On 6/10/2022 4:35 PM, ira.weiny@...el.com wrote:
> > diff --git a/tools/testing/selftests/vm/protection_keys.c b/tools/testing/selftests/vm/protection_keys.c
> > index d0183c381859..43e47de19c0d 100644
> > --- a/tools/testing/selftests/vm/protection_keys.c
> > +++ b/tools/testing/selftests/vm/protection_keys.c
> > @@ -1225,9 +1225,9 @@ void test_pkey_alloc_exhaust(int *ptr, u16 pkey)
> >   		int new_pkey;
> >   		dprintf1("%s() alloc loop: %d\n", __func__, i);
> >   		new_pkey = alloc_pkey();
> > -		dprintf4("%s()::%d, err: %d pkey_reg: 0x%016llx"
> > +		dprintf4("%s()::%d, errno: %d pkey_reg: 0x%016llx"
> 
> What is errno referring to over here?  There are a few things happening in
> alloc_pkey().

Good point, but the only system call in alloc_pkey() is pkey_alloc() so it will
be the errno from there.

In test_pkey_alloc_exhaust() we are expecting the errno to be from pkey_alloc()

...
                if ((new_pkey == -1) && (errno == ENOSPC)) {
...


> I guess it would show the latest error that happened. Does
> errno need to be set to 0 before the call?

Maybe.  Now that I look again errno is printed just below at level 2.

                dprintf2("%s() errno: %d ENOSPC: %d\n", __func__, errno, ENOSPC);

I missed that.

> 
> Also, would it be useful to print the return value (new_pkey) from
> alloc_pkey() here?

Yea that might be useful.  Perhaps change err to new_pkey instead since errno
is already printed.

Ira

> 
> >   				" shadow: 0x%016llx\n",
> > -				__func__, __LINE__, err, __read_pkey_reg(),
> > +				__func__, __LINE__, errno, __read_pkey_reg(),
> >   				shadow_pkey_reg);
> >   		read_pkey_reg(); /* for shadow checking */
> >   		dprintf2("%s() errno: %d ENOSPC: %d\n", __func__, errno, ENOSPC);
> 
> Sohil