I can confirm that running the HWE kernel 5.11.0-27-generic #29~20.04.1-Ubuntu from proposed on our Ubuntu 20.04 test system resolves the problem. Thanks!
-- You received this bug notification because you are a member of Kernel Packages, which is subscribed to linux in Ubuntu. https://bugs.launchpad.net/bugs/1939301 Title: REGRESSION: shiftfs lets sendfile fail with EINVAL Status in linux package in Ubuntu: In Progress Status in linux-hwe-5.11 package in Ubuntu: Invalid Status in linux source package in Focal: Invalid Status in linux-hwe-5.11 source package in Focal: Fix Committed Status in linux-meta-hwe-5.11 source package in Focal: Invalid Status in linux source package in Hirsute: Fix Committed Status in linux-hwe-5.11 source package in Hirsute: Invalid Status in linux-meta-hwe-5.11 source package in Hirsute: Invalid Status in linux source package in Impish: In Progress Status in linux-hwe-5.11 source package in Impish: Invalid Status in linux-meta-hwe-5.11 source package in Impish: Invalid Bug description: With the 5.11 HWE kernel landing for Ubuntu 20.04 we noticed that LXC tools we're using in bionic containers as part of Anbox Cloud start to fail when executed on the 5.11 kernel. A simple reproducer looks like this: 1. Run Ubuntu 20.04 with HWE kernel (linux-generic-hwe-20.04, 5.11.0-25-generic #27~20.04.1-Ubuntu) 2. Install LXD and enable shiftfs $ snap install lxd $ snap set lxd shiftfs.enable true $ snap restart --reload lxd 3. Launch bionic container and run `lxc-info` $ lxc launch ubuntu:b c0 $ lxc shell c0 c0$ apt update c0$ apt install -y lxc-utils root@c1:~# apt show lxc-utils | grep Version Version: 3.0.3-0ubuntu1~18.04.1 c0$ mkdir -p containers/test c0$ touch containers/test/config c0$ lxc-info -P containers -n test Failed to load config for test Failure to retrieve information on containers:test Looking into the failing `lxc-info` call with strace reveals: ... memfd_create(".lxc_config_file", MFD_CLOEXEC) = 4 openat(AT_FDCWD, "containers/test/config", O_RDONLY|O_CLOEXEC) = 5 sendfile(4, 5, NULL, 2147479552) = -1 EINVAL (Invalid argument ... LXC >= 4.0.0 doesn't use sendfile anymore and with that isn't affected. Any other tool using sendfile however is affected and will fail. Bionic is affected as the 3.0.3 version of LXC it includes still uses sendfile. Disabling shiftfs makes things work again and can be considered as a workaround to a certain degree, but not be applicable in all cases. Further analysis with Christian (cbrauner) from the LXD team this morning showed that shiftfs is missing an implementation for the now required slice_read handler in the file_operations structure. So whenever shiftfs is being used, all calls to sendfile will fail because of the missing implementation. The generic handler for this got removed in the following upstream change: https://lore.kernel.org/lkml/20200626075836.1998185-10-...@lst.de/ Christian implemented a quick fix: https://paste.ubuntu.com/p/TPsjfCpnD5/ As of today I don't know of any customer of Anbox Cloud who is affected by this as most of them run with one of our cloud kernels. However as soon as 5.11 rolls out to the cloud kernels, we will hit production systems and cause them to fail. To manage notifications about this bug go to: https://bugs.launchpad.net/ubuntu/+source/linux/+bug/1939301/+subscriptions -- Mailing list: https://launchpad.net/~kernel-packages Post to : kernel-packages@lists.launchpad.net Unsubscribe : https://launchpad.net/~kernel-packages More help : https://help.launchpad.net/ListHelp