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a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1762940030; bh=VaWvuF/ukzI6PWpHBDHmQqomQZveyXgP4iaU8vUBouQ=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=UyDFIVHupVESBO5dKdFJrpimm/QKcIKr0pIBA+/nRs7CPrOokVE1j8R2pbbZo4+D6 LaLcQ4msb6O040l0Xlul+J1I0CxWKJtpzwQpFHibIydSaDzMYJLRAPITnAZrKB/7Xj Cw4xqTjQFeN2a6S3mtZteOzH165g3rvMwinBE0FwcIc/6VSoKC5bUVF5vz1T4grRN3 02cWymyRwrBcC9ero4np0nIOiLCCkVhnPUQXIaF+rfVOWu4buqIhpWHkQya3TZ95al puiWSHBqlsb7mXu0ckqvIpdIYrfcKU/4mAXxe7WT8wnXsdFy2CeSgWtdvibGgEaM8/ 4p8JFjxn7NAEQ== Date: Wed, 12 Nov 2025 10:33:46 +0100 From: Christian Brauner To: Mike Yuan Cc: linux-mm@kvack.org, linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, Luis Chamberlain , Hugh Dickins , stable@vger.kernel.org Subject: Re: [PATCH] shmem: fix tmpfs reconfiguration (remount) when noswap is set Message-ID: <20251112-vorbehalt-heizsysteme-3b11ba2b7ea3@brauner> References: <20251108190930.440685-1-me@yhndnzj.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <20251108190930.440685-1-me@yhndnzj.com> X-Rspam-User: X-Rspamd-Server: rspam11 X-Rspamd-Queue-Id: 295E7180005 X-Stat-Signature: sr3ysfzxdncgfi6ko4ipqm9piw9zjt4t X-HE-Tag: 1762940031-372583 X-HE-Meta: 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 c7LE2Ci0 Y4igpbRGLD4uMo6e/qy6PGMWTc+PXnDr2NcaH/ym9EWpxFdm9EzFb++QXAxIE94EhWgpE6GH+LfvlueiJPAOs7jGmFJ1dlsg7d1fmdYdO4MgSRvhSig/g5KgH/llt+/nJhq0Duf5M0fsfUYCelSXid2Z9J26+Cwt2lPipj1kIgH5+gB5A7KCTLUgcskkQX018HQj2yEvKHaKGMZlv+x2zeeeMF/YoDsvoINzgV8KeRMoH2zKd+Z+xjn4swV6EJvRUjAbHTFi1heK12tqD1Nd8xGd1HnJOecg5tgjH8aQRzT5hTHTrel+gVHtzTzWQpauXPjJZttqNNpzeyNxO2P2JkRRP0V9GVEV1G3OvJl7LMpyKzEBrUQZr/jUDtV2jnn5ZlPqhOrrU0Vwjn/uRUzh38vUq5FlhwJ5PNNC4dAhjJIxaIxo= 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 Sat, Nov 08, 2025 at 07:09:47PM +0000, 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: > --- Reviewed-by: Christian Brauner