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Thu, 27 Nov 2025 20:51:23 -0400 (AST) MIME-Version: 1.0 Date: Thu, 27 Nov 2025 20:51:23 -0400 From: Kurt Fitzner To: Mikulas Patocka Cc: Aaron Rainbolt , Milan Broz , linux-mm@kvack.org, cryptsetup@lists.linux.dev, dm-devel@lists.linux.dev, linux-kernel@vger.kernel.org, adrelanos@whonix.org Subject: Re: Hard system lock-ups when using encrypted swap and RAM is exhausted In-Reply-To: <3f3d871a-6a86-354f-f83d-a871793a4a47@redhat.com> References: <20251111231835.1232ad8f@kf-m2g5> <2b8b83fa-5cf5-4f97-b796-0c738ce3a548@gmail.com> <3f3d871a-6a86-354f-f83d-a871793a4a47@redhat.com> Message-ID: <804601778974c504d42f4423d335a94d@va1der.ca> X-Sender: kurt_cryptsetup@va1der.ca Content-Type: text/plain; charset=US-ASCII; format=flowed Content-Transfer-Encoding: 7bit X-Rspamd-Server: rspam10 X-Rspamd-Queue-Id: 88B8AC000A X-Stat-Signature: ndzj518iwq7uohy67jp9xs45orhrnt1u X-Rspam-User: X-HE-Tag: 1764291084-204489 X-HE-Meta: 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 yqkuCaSJ 3He4GzbO+sSYHSPF+YHJfnvsfgyk/ndqK14YlI7u6F8v+7tLyGsFOJpm36wm7g72CBx2EJgFqUPRVa6fqjTMlHN8jeqAPR71pB8wvDL0236S2UVO4YjCub5afjUJ44C4tN/LZ5huq2PB++CkdkMOUkC0AeJWAAcOCVrbPhWdpHZqNbd6HoXvlmFeABRVWz7kKaFspvDpzE5aR9hfsROV50IS12GeD6Ir8PEANqMjdHINYBBLL1Q8Lvx0ffw== 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 2025-11-27 13:54, Mikulas Patocka wrote: > Encrypted swap file is not supposed to work. Do you have a reference for this? The concept of encrypted swap files has been a valid workflow for a very long time. > So, this is what happened to you - the machine runs out of memory, it > needs to swap out some pages, dm-crypt encrypts the pages and generates > write bios, the write bios are directed to the loop device, the loop > device directs them to the filesystem, the filesystem attempts to > allocate > more memory => deadlock. If it's the filesystem trying to allocate memory on writes to a swap file that is causing a memory allocation/swap race, then any write to a swap file would engender the same result, regardless of encryption. The encryption layer is redundant under the failure mode you propose. I can confirm I have put kernels up to and including 6.14 under heavy memory stress and have never encountered anything that feels like a memory allocation race. All my systems have encrypted swap files. I can't speak toward later kernels, or any bugs that may or may not be presesnt, but I know of nothing to suggest that encrypted swap files remain anything other than an intended feature. Kurt