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); <------ EINVALAfter 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 me@yhndnzj.com Cc: Luis Chamberlain mcgrof@kernel.org Cc: Christian Brauner brauner@kernel.org Cc: Hugh Dickins hughd@google.com Cc: stable@vger.kernel.org
Makes sense to me
Reviewed-by: David Hildenbrand (Red Hat) david@kernel.org