Messages in this thread | | | Date | Fri, 25 Nov 2011 17:54:09 +0100 | From | Oleg Nesterov <> | Subject | Re: [RFC][PATCH 0/3] fork: Add the ability to create tasks with given pids |
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On 11/25, Pavel Emelyanov wrote: > > On 11/25/2011 08:22 PM, Oleg Nesterov wrote: > > On 11/25, Pavel Emelyanov wrote: > >> > >> The proposal is to implement the PR_RESERVE_PID prctl which allocates and puts a > >> pid on the current. The subsequent fork() uses this pid, > > > > Oh. This is subjective, yes, but this doesn't clean to me. > > > > Amd why?? On the running system PR_RESERVE_PID can obviously fail anyway. > > It only helps to avoid the race with another fork. > > No. It can fail if you try to allocate a pid with given number. The API allows for > pid generation. AFAIU this can help with Pedro's requirements to resurrect task with > the same pid value it used to have before.
Yes gdb can do fork() in a row (until it unreserves the pid) and the pid will be the same.
OK, I misunderstood. I thought you insist that PR_RESERVE_PID itself is reliable.
But this can only work in the simplest case. How you can restore the multithread tracee? You need to unreserve/reserve the previous pid, and we have the same problems again, no?
> > Yes, and this task_struct->rsv_pid acts as implicit parameter for the > > next clone(). Doesn't look very nice to me. Plus the code complications. > > Well, the last_pid is also an implicit parameter for the next clone() with sysctl > approach :)
Yes. but it is already here ;)
Oleg.
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