On 08/02, Christian Brauner wrote: > > On Wed, Jul 31, 2019 at 06:12:22PM +0200, Adrian Reber wrote: > > The main motivation to add CLONE_SET_TID to clone3() is CRIU. > > > > To restore a process with the same PID/TID CRIU currently uses > > /proc/sys/kernel/ns_last_pid. It writes the desired (PID - 1) to > > ns_last_pid and then (quickly) does a clone(). This works most of the > > time, but it is racy. It is also slow as it requires multiple syscalls. > > Can you elaborate how this is racy, please. Afaict, CRIU will always > usually restore in a new pid namespace that it controls, right?
Why? No. For example you can checkpoint (not sure this is correct word) a single process in your namespace, then (try to restore) it. > What is > the exact race? something else in the same namespace can fork() right after criu writes the pid-for-restore into ns_last_pid. Oleg.
