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a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1762947890; bh=Wj/4q1C1ArnQ7Q4ixJ7EiiawvGxLIH7JDw3b8s+7UQk=; h=Date:Subject:To:Cc:References:From:In-Reply-To:From; b=FyXu+/73fldy/N9aF3u1xUDUGJiObxFLxZZGQhuJ7inI7zDlB+KnAcT4c2tZlz9sC UKPZDozEAjr1L6hpJF+xTP8CKVu7qTZH2UHes9izH5opdFzdciysPSWizGXeeQ+mej MEPSu1l20VwPcnP75gh82oftOZZvJfc42pUMu0ZOzsv2iqfiwdqkTsm06PShgbY+VX MH23jxelP4g06YyGWqLJJQoeO0oNfOQnO6GELdouoJDl94E2Eq+0JbBM/M7YxoD/rg dZ4K5lVyLs0s9vo04NQf5U250KVefbpOjIdtwl5L8IUVUWS8rq3ok9s3+UpREtyhJs TcUGKdtezFBVA== Message-ID: <9c4cac95-adbf-4236-a872-5213a2a797da@kernel.org> Date: Wed, 12 Nov 2025 12:44:46 +0100 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH] shmem: fix tmpfs reconfiguration (remount) when noswap is set To: Mike Yuan , linux-mm@kvack.org, linux-fsdevel@vger.kernel.org Cc: linux-kernel@vger.kernel.org, Luis Chamberlain , Christian Brauner , Hugh Dickins , stable@vger.kernel.org References: <20251108190930.440685-1-me@yhndnzj.com> From: "David Hildenbrand (Red Hat)" Content-Language: en-US In-Reply-To: <20251108190930.440685-1-me@yhndnzj.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Rspamd-Queue-Id: 747551C000C X-Rspamd-Server: rspam07 X-Stat-Signature: a317goyjfrcz8w3inapuh73ttpa7tnwd X-Rspam-User: X-HE-Tag: 1762947891-437183 X-HE-Meta: U2FsdGVkX1/OoEPuWsH50aaHpJ1fNQ9rdQRiYEbqIv9fYfVZxae0O7qC7IO/VfBBAS6Mt2Y5PKt/T1BxPv7XDlhg3hVFtDczGdQl3dcUMunk00WImvuYR2VJ+h1oJKC9yznxj/SKe3P3svKwFG2vDFfzaV6m1OuVWJzEF9m8aNLwTI8iwTODzV3SmP0r51CYUR+B/I4CM6edvekVD5njiHtKFklMj/IQKn/uK3i7y3omA+27kkY3bNeaJPq0fWamiw5LJdBctoootbJ6Win02amIzFP5AEqw0Sl1Ijikneyi+0IiAwB0h4uxGyn8COtlQxzfRnZJyyFloOqBtNpJbqWSL7p0aM19ly6My/w3ijRvvoDHBeO11mjZhs1nnZ0IQo6dZHHPL8CGjmhE6S2CymfCp4TQ/BzeNGKtDcQIsm6OlH1gKw36WpVTjcEDao9YQWigIl9aAdcCycOQSOjvqxcYiSMuwbknrkbPeFs/qQcXhFvxTk1O1O8cBmj4icRZtkD5NXG4iVzT0EAF0GJqh2fh5h60Z2zHgUG9a8J7gYeAHpwugvoLxB5xoVVEEVLkNfCcGIGAdggBm5WvL5/h5F6OZ9CMyoutfo+K9dpFzhOGYfKzT9jT3Y+XbXm7zINxhD4ofJe0zePkHjZ7pu3MdthGmzMOn/knFrVl/OKuACnrn+3jCkC32hgDHcWX0WQNTT+trVepMynmBfsoFNkAS6NCJYdECq8JYAkbXs/4dZ7gtSkFdNdNJlmwVup0SZQtHxzJ/ZOSpqEEh8DNyOS5vk3EDYm8r+4jwRPH0eU276EGYanxGJRNMRYQ7mlWyyd7dknXg1y0AhJhdUYC9gvGwtSrBM5BudsuH9xReCsr49JOnWU7nQO+zQzf0JbnpJX5+vXgEiUXUgXHW0s6S2IR9dN6m2AET+gq3qssi1yL0CxfRvC+HqhWyibLQXRKhyvdkWnfP+xrrJzZHb4vPAl v0xrV6uH R16ROMME2VecLCwBTphnZKOZU7WyrT6MOKq4ufCgZqZuFTarI+ge0xpCPp8e4lgtYxoms9OHkGrmMo6zHTGEuoBQMmL1V6D9t/b+JquVFlc1PGLAFZd39ehs8yLBtdNpJBEsN8/zC7PmJP2N9ZgMa+3UOh7WCscSvg6z8KG0e126IAQ4OrpQekfoqDxLMgeYQEb4bzvp4NISyBAh+HJ8CWhmkFlUPbCXmtCIVcys2rrUG6TB8T6SLofUd9yMRZdxR7Ysxn+4zSPiK/MbwDGXxwc6BX1KisxO8reFeVXGDfHNamJPMIKmJQT4kJQ02ronKijMS1GpEoWpl4FtCELTMH3p7KpyHoBCdpwn30DB5Ltbu99MGtiE0bLqLpXW65H5LwMhc 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 08.11.25 20:09, Mike Yuan wrote: > In systemd we're trying to switch the internal credentials setup logic > to new mount API [1], and I noticed fsconfig(FSCONFIG_CMD_RECONFIGURE) > consistently fails on tmpfs with noswap option. This can be trivially > reproduced with the following: > > ``` > int fs_fd = fsopen("tmpfs", 0); > fsconfig(fs_fd, FSCONFIG_SET_FLAG, "noswap", NULL, 0); > fsconfig(fs_fd, FSCONFIG_CMD_CREATE, NULL, NULL, 0); > fsmount(fs_fd, 0, 0); > fsconfig(fs_fd, FSCONFIG_CMD_RECONFIGURE, NULL, NULL, 0); <------ EINVAL > ``` > > After some digging the culprit is shmem_reconfigure() rejecting > !(ctx->seen & SHMEM_SEEN_NOSWAP) && sbinfo->noswap, which is bogus > as ctx->seen serves as a mask for whether certain options are touched > at all. On top of that, noswap option doesn't use fsparam_flag_no, > hence it's not really possible to "reenable" swap to begin with. > Drop the check and redundant SHMEM_SEEN_NOSWAP flag. > > [1] https://github.com/systemd/systemd/pull/39637 > > Fixes: 2c6efe9cf2d7 ("shmem: add support to ignore swap") > Signed-off-by: Mike Yuan > Cc: Luis Chamberlain > Cc: Christian Brauner > Cc: Hugh Dickins > Cc: > --- Makes sense to me Reviewed-by: David Hildenbrand (Red Hat) -- Cheers David