Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) client-ip=23.128.96.18;
From:   Song Liu <songliubraving@fb.com>
To:     Peter Zijlstra <peterz@infradead.org>
CC:     bpf <bpf@vger.kernel.org>, Networking <netdev@vger.kernel.org>,
        linux-kernel <linux-kernel@vger.kernel.org>,
        Alexei Starovoitov <ast@kernel.org>,
        Daniel Borkmann <daniel@iogearbox.net>,
        Kernel Team <Kernel-team@fb.com>,
        john fastabend <john.fastabend@gmail.com>,
        "kpsingh@chromium.org" <kpsingh@chromium.org>
Subject: Re: [PATCH v2 bpf-next 1/4] perf: export get/put_chain_entry()
Thread-Topic: [PATCH v2 bpf-next 1/4] perf: export get/put_chain_entry()
Thread-Index: AQHWS06t5H2BZnsAuEuKRuZX7jQ17qjqu3gAgACvs4A=
Date:   Fri, 26 Jun 2020 21:29:38 +0000
Message-ID: <6A3C511C-4749-4672-988C-AA8149FB6355@fb.com>
References: <20200626001332.1554603-1-songliubraving@fb.com>
 <20200626001332.1554603-2-songliubraving@fb.com>
 <20200626110046.GB4817@hirez.programming.kicks-ass.net>
In-Reply-To: <20200626110046.GB4817@hirez.programming.kicks-ass.net>
Accept-Language: en-US
Content-Language: en-US
Content-Type: text/plain; charset="us-ascii"
Content-ID: <00A4AEF1A6F3A74C9B8CBE62837BB472@namprd15.prod.outlook.com>
Content-Transfer-Encoding: quoted-printable
MIME-Version: 1.0
X-MS-Exchange-CrossTenant-Network-Message-Id: 8ed4d8d1-6596-454e-89f5-08d81a1807dc
X-MS-Exchange-CrossTenant-originalarrivaltime: 26 Jun 2020 21:29:38.1479
 (UTC)
X-MS-Exchange-CrossTenant-fromentityheader: Hosted
X-MS-Exchange-CrossTenant-id: 8ae927fe-1255-47a7-a2af-5f3a069daaa2
X-MS-Exchange-CrossTenant-mailboxtype: HOSTED
X-MS-Exchange-CrossTenant-userprincipalname: fzTYFJ4IIF3DbqVf/co9cDpUeeV3ur+dimtceI+WD2E1gR7bX8M1CPgujkCL5gEyGb1R8vY2ZQcoVOOPt6ib/A==
X-MS-Exchange-Transport-CrossTenantHeadersStamped: BYAPR15MB2952
X-OriginatorOrg: fb.com
X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10434:6.0.216,18.0.687
 definitions=2020-06-26_12:2020-06-26,2020-06-26 signatures=0
X-Proofpoint-Spam-Details: rule=fb_default_notspam policy=fb_default score=0 mlxscore=0
 lowpriorityscore=0 cotscore=-2147483648 spamscore=0 suspectscore=0
 adultscore=0 impostorscore=0 mlxlogscore=999 priorityscore=1501
 clxscore=1015 malwarescore=0 phishscore=0 bulkscore=0 classifier=spam
 adjust=0 reason=mlx scancount=1 engine=8.12.0-2004280000
 definitions=main-2006260150
X-FB-Internal: deliver
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk
List-ID: <linux-kernel.vger.kernel.org>
X-Mailing-List: linux-kernel@vger.kernel.org


> On Jun 26, 2020, at 4:00 AM, Peter Zijlstra <peterz@infradead.org> wrote:
>=20
> On Thu, Jun 25, 2020 at 05:13:29PM -0700, Song Liu wrote:
>> This would be used by bpf stack mapo.
>=20
> Would it make sense to sanitize the API a little before exposing it?

I will fold this in the next version.=20

Thanks,
Song

>=20
> diff --git a/kernel/events/callchain.c b/kernel/events/callchain.c
> index 334d48b16c36..016894b0d2c2 100644
> --- a/kernel/events/callchain.c
> +++ b/kernel/events/callchain.c
> @@ -159,8 +159,10 @@ static struct perf_callchain_entry *get_callchain_en=
try(int *rctx)
> 		return NULL;
>=20
> 	entries =3D rcu_dereference(callchain_cpus_entries);
> -	if (!entries)
> +	if (!entries) {
> +		put_recursion_context(this_cpu_ptr(callchain_recursion), rctx);
> 		return NULL;
> +	}
>=20
> 	cpu =3D smp_processor_id();
>=20
> @@ -183,12 +185,9 @@ get_perf_callchain(struct pt_regs *regs, u32 init_nr=
, bool kernel, bool user,
> 	int rctx;
>=20
> 	entry =3D get_callchain_entry(&rctx);
> -	if (rctx =3D=3D -1)
> +	if (!entry || rctx =3D=3D -1)
> 		return NULL;
>=20
> -	if (!entry)
> -		goto exit_put;
> -
> 	ctx.entry     =3D entry;
> 	ctx.max_stack =3D max_stack;
> 	ctx.nr	      =3D entry->nr =3D init_nr;