Messages in this thread | ![/](/images/icornerl.gif) | | From | Christian Brauner <> | Date | Fri, 2 Aug 2019 15:50:54 +0200 | Subject | Re: [PATCH v2 1/2] fork: extend clone3() to support CLONE_SET_TID |
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On Fri, Aug 02, 2019 at 03:30:01PM +0200, Oleg Nesterov wrote: > 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.
Ok, that makes sense. :) My CRIU userspace knowledge is sporadic, so I'm not sure how exactly it restores process trees in pid namespaces and what workloads this would especially help with.
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