Received-SPF: pass (google.com: domain of linux-kernel+bounces-206260-linux.lists.archive=gmail.com@vger.kernel.org designates 2604:1380:45d1:ec00::1 as permitted sender) client-ip=2604:1380:45d1:ec00::1;
Date: Fri, 7 Jun 2024 10:25:29 -0400
From: "Liam R. Howlett" <Liam.Howlett@oracle.com>
To: Suren Baghdasaryan <surenb@google.com>
Cc: Andrii Nakryiko <andrii.nakryiko@gmail.com>,
        Vlastimil Babka <vbabka@suse.cz>, sidhartha.kumar@oracle.com,
        Matthew Wilcox <willy@infradead.org>,
        Lorenzo Stoakes <lstoakes@gmail.com>, linux-fsdevel@vger.kernel.org,
        bpf@vger.kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org
Subject: Re: [RFC PATCH 1/5] mm/mmap: Correctly position vma_iterator in
 __split_vma()
Message-ID: <mg2orzdqididfjexb7mj7gep3guehtdzamjn2v5a5vce7cd2ch@uvjjc2xzv7ao>
Mail-Followup-To: "Liam R. Howlett" <Liam.Howlett@oracle.com>, 
	Suren Baghdasaryan <surenb@google.com>, Andrii Nakryiko <andrii.nakryiko@gmail.com>, 
	Vlastimil Babka <vbabka@suse.cz>, sidhartha.kumar@oracle.com, Matthew Wilcox <willy@infradead.org>, 
	Lorenzo Stoakes <lstoakes@gmail.com>, linux-fsdevel@vger.kernel.org, bpf@vger.kernel.org, 
	linux-mm@kvack.org, linux-kernel@vger.kernel.org
References: <20240531163217.1584450-1-Liam.Howlett@oracle.com>
 <20240531163217.1584450-2-Liam.Howlett@oracle.com>
 <CAJuCfpHqDNGM=6+TX4xE-YY91fETSM+r70ZdgxUyw=9X+3qQCQ@mail.gmail.com>
Content-Type: text/plain; charset=utf-8
Content-Disposition: inline
Content-Transfer-Encoding: quoted-printable
In-Reply-To: <CAJuCfpHqDNGM=6+TX4xE-YY91fETSM+r70ZdgxUyw=9X+3qQCQ@mail.gmail.com>
User-Agent: NeoMutt/20231103
Precedence: bulk
MIME-Version: 1.0
X-MS-Exchange-AntiSpam-MessageData-ChunkCount: 1
X-MS-Exchange-AntiSpam-MessageData-0: 
	=?utf-8?B?di9IZ1U1ald0SklNekNBNm9nMGtCT21SQUhoRDZ0UjFEOHovMkk1TkhrYTE1?=
 =?utf-8?B?S1lZRDZla1Zza3NTRm52bXh2RlZXVjdqWG1GSDBMR1ArNGVuRmNtbms5MzdQ?=
 =?utf-8?B?cnFCUlNlaWNDVHNPT3pub0ZoL3V0MW1TWERxL3BUS3Vkb3NWY1dDb3RZOTJF?=
 =?utf-8?B?RVh2TFg2ZSt2WUUxT2d0aytVUkwxcEtmb0JTNklSMFBGMEZqYWNtemNXblBx?=
 =?utf-8?B?Yko2TVJNU00vSGNqejhxeHFUeFVLS3ZSdVFkaGo1bUd1RlM0c3FKTkJRbkIy?=
 =?utf-8?B?L3F3aWJLNGZ4MVBsVzRaclI3RG1YSi9NenBUbkpQQXRYemh4WnhZN1YvQnpT?=
 =?utf-8?B?QUx4V3VFaWdiU3RjODFyemFzYmtMRWUra3NxdkRZWVE3Q28wd3FjK1pLTlpl?=
 =?utf-8?B?M2tvcjUzbE80aUhCK0ZPY3owRUxZbEZGM0JDNy9mVkdSbkxmOTAzZmJGOGNN?=
 =?utf-8?B?YTNWY1V5eWlVM2tQclliMDJic09ncENhNkY0Nk8zVFhUZ0wvN3Y0ZFBOanVq?=
 =?utf-8?B?N1lLNXBYTVJvcFpJVDdNZllYa0h4d3Vtd2RHV2k1d2s2Y2ZOTjFyNzRZZ1RB?=
 =?utf-8?B?TGRKYlpSQlkwdTNwQWp3cWxLYWp5bC94UkEwOTJjSVltVVZucGdWL2Z4ayt2?=
 =?utf-8?B?OWNZZFl2d09aS1NJTjZncTdJS0x4RlhtdU80dWIzQU9xWDRieVFtdHpTWHR4?=
 =?utf-8?B?M2prU2pJdDU4R3ZqR1A4VjdqY0pKNmFDOXZPSDVxQnhJU3JCQ09KNURXTzhZ?=
 =?utf-8?B?djFlMlNOVzJvTjcyK3RuSUhTQkl1R0dBd0NNRDZPSTdZL3gyRENuL2VwWFo0?=
 =?utf-8?B?VDNTVDVQaTlGQWhidkMwRXliMVQ2cWRuQnk5bTZyZHk2SkNXSWM3NEE0VzNY?=
 =?utf-8?B?blZUTFArNnJ3bkFkaW1YUWFrclhkL1NrVG1hUmN1QmQwNVpPdWNXdkZqVS9t?=
 =?utf-8?B?c05kRjBTOGFVRjJQRVFUQkxVMWVSZVdML0s5eSs2ZWtwTUFCYXl0U1ZraVNs?=
 =?utf-8?B?V2JCeFFJQnNGOHJFMDI4YXQ0dHdNZDNTRGFLZ1NEUllyOWFZYWxCWm1XbkR2?=
 =?utf-8?B?d3NMY2dGTnd1OVIzNXRpYnFLd1RpQmpMdXBTWmNtTnphcW1qSGRnUkdMVHNq?=
 =?utf-8?B?NVNLVGU4cmwrbU1YWWIzL1MxT0NPeURjaWhMeDJCbkZpamZVKzV1QVpHaVo5?=
 =?utf-8?B?M0d2T09XK1N4bUhXOWliUU1DQTBqdzVRWlFkT2xmaW1xRjMrTVc5RXFld0xV?=
 =?utf-8?B?S1pVdHhoaWtlNXdtRUtlRGZzSDhnNUpScmdMRzNOVDNIanFFK1MvRFpnckpU?=
 =?utf-8?B?MFQrZGl4RFQydmU0Nk95V3ZCL2o2WE9aVlFzNXZhcG1VTU9xQ3ZUNjNzQU5I?=
 =?utf-8?B?aXBHcjNFVE9laEJhZEdEbVNKODNrWjdUUW5hNnY4aWtYOCt5MmlqdUIydHhO?=
 =?utf-8?B?eU92N3Zyc0VtMTZndW9rc29tUVhhdlJRYmFXTThsUFViRXBKU0RTS3hTZXFM?=
 =?utf-8?B?b00vTkRtZzd6TVJiS1ErUG5ZVENRcFdIcldOQ0lPVVg0bFJRS2dvZUJNUlFY?=
 =?utf-8?B?N24wWU9KRTlxNWllZGxWaG93bFJKclFzSEhnRDFCamxNSDBNalM5NDN2aEFk?=
 =?utf-8?B?MFhTR3RqRy9XSHNzRjh6R0RsSkFDbHd6aFh0SVlCM1RJTkhMY2tNbGFSZnhT?=
 =?utf-8?B?U3JiY25TSDg3YXM0RDd2Mmh6STkrVXUza2JaMWpLM1RDbW5KOERrcTUyUGUv?=
 =?utf-8?B?bTRGMDFXSEE4TngwRVljVlIvTkZQMUYzeHVNZks0ek55UHdIZHNkaUlTaFJ1?=
 =?utf-8?B?NEdqWmpSNXNGMVdmRmNaT0pUampweWMwbzM3K1ZJMlJUa2VEUm1BZkNTenMz?=
 =?utf-8?B?ay9SU2NXNzV2eVBwSG43Y0pXcXc2R0hRc0JuSDI4YVk0WE9tbWFKMmhVR255?=
 =?utf-8?B?WE9Mb3ZJTG9IK3lqSnh3bkNGQ3RYcU9UczFSbGdXa3pGSTgvd2l1MnJRTTlR?=
 =?utf-8?B?d0h0WUlMdy9kaGFsaDJLdnRiMGo1RkIvekdoaVdyQVUyR09OejZEUGc1YUtn?=
 =?utf-8?B?VVlrc0Mwem82M0NGSTl4cVRscng2YkJ0MlVUbTBJamZsT1QrVXBqM29uZEJB?=
 =?utf-8?B?MzVBVGZHODk5QW1FZkdBakg1aDJtNmx3aVJkZEhtRzZ2b2Q2ZzlyTm9wNC9k?=
 =?utf-8?B?YXc9PQ==?=
X-MS-Exchange-AntiSpam-ExternalHop-MessageData-ChunkCount: 1
X-MS-Exchange-AntiSpam-ExternalHop-MessageData-0: 
	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
X-OriginatorOrg: oracle.com
X-MS-Exchange-CrossTenant-Network-Message-Id: a460b2e1-0d5d-428e-ec6e-08dc86fdb09f
X-MS-Exchange-CrossTenant-AuthSource: DS0PR10MB7933.namprd10.prod.outlook.com
X-MS-Exchange-CrossTenant-AuthAs: Internal
X-MS-Exchange-CrossTenant-OriginalArrivalTime: 07 Jun 2024 14:25:32.9246
 (UTC)
X-MS-Exchange-CrossTenant-FromEntityHeader: Hosted
X-MS-Exchange-CrossTenant-Id: 4e2c6054-71cb-48f1-bd6c-3a9705aca71b
X-MS-Exchange-CrossTenant-MailboxType: HOSTED
X-MS-Exchange-CrossTenant-UserPrincipalName: DJC/jt1FM/q26+188xqITZeeEg1JfbET7JTf1RG80h4TtjeRCVzxdEVQWgZaWRBpicxhp95OyzZcRlRPF439KQ==
X-MS-Exchange-Transport-CrossTenantHeadersStamped: MW4PR10MB6322
X-Proofpoint-Virus-Version: vendor=baseguard
 engine=ICAP:2.0.293,Aquarius:18.0.1039,Hydra:6.0.680,FMLib:17.12.28.16
 definitions=2024-06-07_08,2024-06-06_02,2024-05-17_01
X-Proofpoint-Spam-Details: rule=notspam policy=default score=0 mlxscore=0 malwarescore=0 adultscore=0
 phishscore=0 suspectscore=0 bulkscore=0 spamscore=0 mlxlogscore=999
 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2405010000
 definitions=main-2406070106
X-Proofpoint-GUID: nw2OJqLpBeOjwzld31BTMxdbKR1RzeGd
X-Proofpoint-ORIG-GUID: nw2OJqLpBeOjwzld31BTMxdbKR1RzeGd

* Suren Baghdasaryan <surenb@google.com> [240605 20:51]:
> On Fri, May 31, 2024 at 9:33=E2=80=AFAM Liam R. Howlett <Liam.Howlett@ora=
cle.com> wrote:
> >
> > The vma iterator may be left pointing to the newly created vma.  This
> > happens when inserting the new vma at the end of the old vma
> > (!new_below).
> >
> > The incorrect position in the vma iterator is not exposed currently
> > since the vma iterator is repositioned in the munmap path and is not
> > reused in any of the other paths.
> >
> > This has limited impact in the current code, but is required for future
> > changes.
> >
> > Fixes: b2b3b886738f ("mm: don't use __vma_adjust() in __split_vma()")
> > Signed-off-by: Liam R. Howlett <Liam.Howlett@oracle.com>
> > ---
> >  mm/mmap.c | 3 +++
> >  1 file changed, 3 insertions(+)
> >
> > diff --git a/mm/mmap.c b/mm/mmap.c
> > index 83b4682ec85c..31d464e6a656 100644
> > --- a/mm/mmap.c
> > +++ b/mm/mmap.c
> > @@ -2442,6 +2442,9 @@ static int __split_vma(struct vma_iterator *vmi, =
struct vm_area_struct *vma,
> >         /* Success. */
> >         if (new_below)
> >                 vma_next(vmi);
> > +       else
> > +               vma_prev(vmi);
> > +
>=20
> IIUC the goal is to always point vmi to the old (original) vma? If so,
> then change LGTM.

Yes, we need the iterator to keep pointing to the original VMAs, I think
this makes sense.  I will update the function comment in the next
revision to state as much.

>=20
> Reviewed-by: Suren Baghdasaryan <surenb@google.com>
>=20
> >         return 0;
> >
> >  out_free_mpol:
> > --
> > 2.43.0
> >