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charset="us-ascii" Content-ID: <9DE781A594B98E4EB961CFA26CC32854@namprd15.prod.outlook.com> Content-Transfer-Encoding: quoted-printable MIME-Version: 1.0 X-MS-Exchange-CrossTenant-Network-Message-Id: ee927282-3083-4aab-f95c-08d6e4526f70 X-MS-Exchange-CrossTenant-originalarrivaltime: 29 May 2019 16:26:43.0828 (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: guro@fb.com X-MS-Exchange-Transport-CrossTenantHeadersStamped: BYAPR15MB3029 X-OriginatorOrg: fb.com X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10434:,, definitions=2019-05-29_08:,, signatures=0 X-Proofpoint-Spam-Details: rule=fb_default_notspam policy=fb_default score=0 priorityscore=1501 malwarescore=0 suspectscore=0 phishscore=0 bulkscore=0 spamscore=0 clxscore=1015 lowpriorityscore=0 mlxscore=0 impostorscore=0 mlxlogscore=999 adultscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.0.1-1810050000 definitions=main-1905290107 X-FB-Internal: deliver X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Wed, May 29, 2019 at 03:58:17PM +0200, Uladzislau Rezki wrote: > Hello, Roman! >=20 > > > Move the BUG_ON()/RB_EMPTY_NODE() check under unlink_va() > > > function, it means if an empty node gets freed it is a BUG > > > thus is considered as faulty behaviour. > >=20 > > It's not exactly clear from the description, why it's better. > >=20 > It is rather about if "unlink" happens on unhandled node it is > faulty behavior. Something that clearly written in stone. We used > to call "unlink" on detached node during merge, but after: >=20 > [PATCH v3 3/4] mm/vmap: get rid of one single unlink_va() when merge >=20 > it is not supposed to be ever happened across the logic. >=20 > > > > Also, do we really need a BUG_ON() in either place? > >=20 > Historically we used to have the BUG_ON there. We can get rid of it > for sure. But in this case, it would be harder to find a head or tail > of it when the crash occurs, soon or later. >=20 > > Isn't something like this better? > >=20 > > diff --git a/mm/vmalloc.c b/mm/vmalloc.c > > index c42872ed82ac..2df0e86d6aff 100644 > > --- a/mm/vmalloc.c > > +++ b/mm/vmalloc.c > > @@ -1118,7 +1118,8 @@ EXPORT_SYMBOL_GPL(unregister_vmap_purge_notifier)= ; > > =20 > > static void __free_vmap_area(struct vmap_area *va) > > { > > - BUG_ON(RB_EMPTY_NODE(&va->rb_node)); > > + if (WARN_ON_ONCE(RB_EMPTY_NODE(&va->rb_node))) > > + return; > > > I was thinking about WARN_ON_ONCE. The concern was about if the > message gets lost due to kernel ring buffer. Therefore i used that. > I am not sure if we have something like WARN_ONE_RATELIMIT that > would be the best i think. At least it would indicate if a warning > happens periodically or not. >=20 > Any thoughts? Hello, Uladzislau! I don't have a strong opinion here. If you're worried about losing the mess= age, WARN_ON() should be fine here. I don't think that this event will happen of= ten, if at all. Thanks!