linux-kernel - Re: [PATCH v3 3/3] KEYS: Use kvmalloc() to better handle large buffer allocation

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Message-ID: <74ec00b8-d7a7-0035-d650-710415660926@redhat.com>
Date:   Sun, 15 Mar 2020 18:01:51 -0400
From:   Waiman Long <longman@...hat.com>
To:     Jarkko Sakkinen <jarkko.sakkinen@...ux.intel.com>
Cc:     Eric Biggers <ebiggers@...nel.org>,
        David Howells <dhowells@...hat.com>,
        James Morris <jmorris@...ei.org>,
        "Serge E. Hallyn" <serge@...lyn.com>,
        Mimi Zohar <zohar@...ux.ibm.com>, keyrings@...r.kernel.org,
        linux-kernel@...r.kernel.org,
        linux-security-module@...r.kernel.org,
        linux-integrity@...r.kernel.org,
        Sumit Garg <sumit.garg@...aro.org>,
        Jerry Snitselaar <jsnitsel@...hat.com>,
        Roberto Sassu <roberto.sassu@...wei.com>,
        Chris von Recklinghausen <crecklin@...hat.com>
Subject: Re: [PATCH v3 3/3] KEYS: Use kvmalloc() to better handle large buffer
 allocation

On 3/15/20 5:52 PM, Jarkko Sakkinen wrote:
> On Fri, Mar 13, 2020 at 01:49:57PM -0400, Waiman Long wrote:
>>>>  			if (!tmpbuf || unlikely(ret > tmpbuflen)) {
>>>>  				if (unlikely(tmpbuf))
>>>> -					kzfree(tmpbuf);
>>>> +					__kvzfree(tmpbuf, tmpbuflen);
>>> Both kzfree() and __kvzfree() handle a NULL pointer, so there's no need for the
>>> NULL check first.
>>>
>> I would like to keep this one because of the unlikely annotation.
> What (measurable) gain does it bring anyway?

It is not a performance issue. I just want to indicate that the need to
free should not happen at all. It match the unlikely tag in the if
condition above.

Cheers,
Longman