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charset="us-ascii" Content-Transfer-Encoding: quoted-printable MIME-Version: 1.0 X-MS-Exchange-CrossTenant-AuthAs: Internal X-MS-Exchange-CrossTenant-AuthSource: IA0PR11MB7185.namprd11.prod.outlook.com X-MS-Exchange-CrossTenant-Network-Message-Id: 54f5657d-4baf-4600-55da-08ddb3f327f7 X-MS-Exchange-CrossTenant-originalarrivaltime: 25 Jun 2025 14:18:28.5066 (UTC) X-MS-Exchange-CrossTenant-fromentityheader: Hosted X-MS-Exchange-CrossTenant-id: 46c98d88-e344-4ed4-8496-4ed7712e255d X-MS-Exchange-CrossTenant-mailboxtype: HOSTED X-MS-Exchange-CrossTenant-userprincipalname: b49OYnvlCAq4wfpefjqgVNGOFns8nopQFXDNsPPgUc7SgWerSEupe78rHcoUjF2ZwnAlaaWtiORr5cs2yhCiaYlyM6yIcwKTVvVxrr/PNik= X-MS-Exchange-Transport-CrossTenantHeadersStamped: DS4PPF07B018B9F X-OriginatorOrg: intel.com X-Rspam-User: X-Rspamd-Server: rspam04 X-Rspamd-Queue-Id: 4134FC000E X-Stat-Signature: 5yx9man15xfs4spp4ubosw6g98wekpbm X-HE-Tag: 1750861129-144305 X-HE-Meta: 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 Y4nuO9Kh 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 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: List-Subscribe: List-Unsubscribe: Hi Andrew, > Subject: Re: [PATCH] mm/hugetlb: Don't crash when allocating a folio if > there are no resv >=20 > On Thu, 19 Jun 2025 05:30:52 +0000 "Kasireddy, Vivek" > wrote: >=20 > > Hi Andrew, Anshuman, > > > > > Subject: Re: [PATCH] mm/hugetlb: Don't crash when allocating a folio = if > there > > > are no resv > > > > > > On Wed, 18 Jun 2025 12:14:49 +0530 Anshuman Khandual > > > wrote: > > > > > > > > Therefore, prevent the above crash by replacing the VM_BUG_ON() > > > > > with WARN_ON_ONCE() as there is no need to crash the system in > > > > > this situation and instead we could just warn and fail the > > > > > allocation. > > > > > > > > Why there are no reserved huge pages in such situations and also ho= w > > > > likely this might happen ? Is it recoverable ? > > As described in the commit message above, the specific situation where > this > > happens is when we try to pin memfd folios before they are faulted-in. > > Although, this is a valid thing to do, it is not the regular or the com= mon > > use-case. Let me explain this further with the following scenarios: > > 1) hugetlbfs_file_mmap() > > memfd_alloc_folio() > > hugetlb_fault() > > > > 2) memfd_alloc_folio() > > hugetlbfs_file_mmap() > > hugetlb_fault() > > > > 3) hugetlbfs_file_mmap() > > hugetlb_fault() > > alloc_hugetlb_folio() > > > > 3) is the most common use-case where first a memfd is allocated followe= d > > by mmap(), user writes/updates and then the relevant folios are pinned > > (memfd_pin_folios()). The BUG this patch is fixing occurs in 2) because= we > > try to pin the folios before hugetlbfs_file_mmap() is called. So, in th= is > > situation we try to allocate the folios before pinning them but since w= e > did > > not make any reservations, resv_huge_pages would be 0, leading to this > issue. >=20 > Cool, thanks, I'll paste that into the changelog ;) >=20 > So if this code path is rare but expected and normal, should we be > emitting this warning at all? I think it would be OK to drop the warning. Otherwise, Syzbot would continu= e to flag this issue. Thanks, Vivek >=20 > > > I can't find any mailing report/discussion of this. The Closes: take= s > > > us to the syskaller report which is a bit of a dead end. > > My understanding is that the Closes tag can be associated with a URL fo= r > > a public bugtracker like Syzkaller. Would the following be a better Clo= ses > link: > > > https://lore.kernel.org/all/677928b5.050a0220.3b53b0.004d.GAE@google.co > m/T/ >=20 > I'll add that - the more the merrier. >=20 > > > > > > I agree with the patch - converting a BUG into a WARN+recover is a go= od > > > thing but as far as I can tell, we don't know what's causing this > > > situation. > > > > > > syskaller has a C reproducer, if anyone is feeling brave. > > The udmabuf selftest added in patch #3 of the other series can also > reproduce > > this issue and is a lot simpler. > > > > Thanks, > > Vivek