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b=JrwfRcOxX33CPFzX9PJ7i1WA8k2xEl10PvklNKm6TqQgAHGyEGImFnxuHYnXwnJzt ubu5E+Qnfrtj88xfTyoWVDTzDHFJMNu4yWJkDAPySqX5iGyHprDtYtSZ2U+6x+/RL5 Sw8j9+rU2HOYfTa6IN5RPuipDKhMXU9o/kCq+itE= Date: Wed, 18 Jun 2025 17:02:48 -0700 From: Andrew Morton To: Anshuman Khandual Cc: Vivek Kasireddy , dri-devel@lists.freedesktop.org, linux-mm@kvack.org, syzbot+a504cb5bae4fe117ba94@syzkaller.appspotmail.com, Steve Sistare , Muchun Song , David Hildenbrand Subject: Re: [PATCH] mm/hugetlb: Don't crash when allocating a folio if there are no resv Message-Id: <20250618170248.89ff5c3d3fe23233424fd4da@linux-foundation.org> In-Reply-To: <99b9f7c8-62e0-4500-b4f1-0efdb73bf502@arm.com> References: <20250618052840.1036164-1-vivek.kasireddy@intel.com> <99b9f7c8-62e0-4500-b4f1-0efdb73bf502@arm.com> X-Mailer: Sylpheed 3.7.0 (GTK+ 2.24.33; x86_64-pc-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit X-Stat-Signature: spg6rwfkw6aippo6fewdth6ph8ogejgu X-Rspamd-Queue-Id: A0A18180003 X-Rspam-User: X-Rspamd-Server: rspam06 X-HE-Tag: 1750291370-519113 X-HE-Meta: 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 aQp34JaT +cwVtk7xN7iD7pECWDz6s51gIuuSHcy4sv4efldXW5l+ClKxl79PhnwI7axSD4huHCY08+lzZsgacz4/VGiIafetVyoE4ha8ra6aeNU+LxmfMkwVkETJhosJUnWBsMh0KqyCCqnowvcJTRSdrK6m5j9QIYTbM+T2XhFANzhAhufTLw5BMVFXHTzcibCuir9Ti3198p3Bv1qwKGqRKD6W45eE/yop2p3LvMn2pCQpMfd/9CWqLlR8xkRj6oU0IASIyi4stidDg038Udw5ew01+1+L7L+3GclHlesQhsJBOgZdgtFJFqgcKUXy7VK1PHgFpEcoiG60IES/DYKnOYeFi729KAuMu6x1E4x2ZtQuVUW5k73Ye7rmdp5BqohPDM86QOWpcOG5cGsf6yeRGo+RM8sLgrCuvC7SyXQpxROE40a2x8mCFmwYiOxpTJD8sRafo8pCatieabp5m3pZ7aTcPF69Mpo85YtEypTzdDqr43DDPi5DrbJ0j4gxYKR0R7oAphJRiCcwS1p8Nfuk= 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: 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 how > likely this might happen ? Is it recoverable ? I'm suspecting we don't know. > > > > Fixes: 26a8ea80929c ("mm/hugetlb: fix memfd_pin_folios resv_huge_pages leak") How was this arrived at? This is merely the patch which added the assertion. > > Reported-by: syzbot+a504cb5bae4fe117ba94@syzkaller.appspotmail.com > > Closes: https://syzkaller.appspot.com/bug?extid=a504cb5bae4fe117ba94 I can't find any mailing report/discussion of this. The Closes: takes us to the syskaller report which is a bit of a dead end. I agree with the patch - converting a BUG into a WARN+recover is a good 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.