On 04/23/2015 01:51 AM, Al Viro wrote: > On Thu, Apr 23, 2015 at 01:41:02AM +0200, Mickaël Salaün wrote: >> Hi, >> >> For your information, the commit bbd5192412fdedbae00888316bfe350bf89d0458 (proc: Update proc_flush_task_mnt to use d_invalidate), in the v3.17, break some userland use of procfs. >> >> In a user namespace, I'm using /proc/<pid>/task/<tid>/fdinfo to mount a tmpfs, chdir into it, terminate the <tid> thread, and use the tmpfs as a private working directory for PID 1. This trick is useful to disconnect/d_drop a directory from the current file system and make it inaccessible to the other processes (kind of an O_TMPFILE for directory). >> >> With the v3.17 this is no more possible because it's no more possible to mount anything in this tmpfs nor use the previously mounted file systems in this tmpfs. >> >> The new d_invalidate is really good to lazily invalidate/umount an entire hierarchy but I'm not sure the intention was to remove this useful "feature" ;) > > And what will happen if you mount stuff there and exit? Dirty filesystem > after reboot? > I didn't notice any but only do tmpfs or bind mounts because of user namespace anyway.
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