Messages in this thread | | | From | Gargi Sharma <> | Date | Sun, 22 Oct 2017 08:05:44 +0000 | Subject | Re: [v6,1/2] pid: Replace pid bitmap implementation with IDR API |
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On Fri, Oct 20, 2017 at 6:21 PM, Andrei Vagin <avagin@virtuozzo.com> wrote: > On Fri, Oct 20, 2017 at 05:06:47PM +0100, Gargi Sharma wrote: >> On Thu, Oct 19, 2017 at 5:18 PM, Oleg Nesterov <oleg@redhat.com> wrote: >> > On 10/19, Andrei Vagin wrote: >> >> >> >> Hi Gargi, >> >> >> >> This patch breaks CRIU, because it changes a meaning of ns_last_pid. >> > >> > ... >> > >> >> > @@ -311,7 +297,7 @@ static int pid_ns_ctl_handler(struct ctl_table *table, int write, >> >> > * it should synchronize its usage with external means. >> >> > */ >> >> > >> >> > - tmp.data = &pid_ns->last_pid; >> >> > + tmp.data = &pid_ns->idr.idr_next; >> > >> > Ah, yes, off-by-one error... >> > >> > Gargi, I don't think you need to make another version, I'd suggest you to send >> > the trivial fix to Andrew, afaics you just need to replace these 2 lines with >> > >> > unsigned int last; >> > int err; >> > >> > tmp.data = &last; >> > err = proc_dointvec_minmax(&tmp, write, buffer, lenp, ppos); >> > if (!err) >> > idr_set_cursor(&pid_ns->idr, last + 1); >> > return err; >> I'm not sure entirely understand how this takes care of rolling over of PIDs? >> Can we ignore that? If yes, won't the tests for CRIU still break? > > Gargi, I don't understand what you mean. Could you elaborate? Do you > mean a case when idr_next is bigger than pid_max? I think this logic > remains the same what we had before switching to idr.
When the PIDs are allocated, if the allocation exceeds pid_max wraps around and starts allocating PIDs starting from pid_min. I'm not sure if idr_set_cursor(&pid_ns->idr, pid_ns->idr.idr_next + 1) takes care of that.
Gargi > > CRIU tests works with a following patch. It is slightly modified version > of Oleg's patch. > > diff --git a/kernel/pid_namespace.c b/kernel/pid_namespace.c > index fea2c24..1c791b3 100644 > --- a/kernel/pid_namespace.c > +++ b/kernel/pid_namespace.c > @@ -287,6 +287,7 @@ static int pid_ns_ctl_handler(struct ctl_table > *table, int write, > { > struct pid_namespace *pid_ns = task_active_pid_ns(current); > struct ctl_table tmp = *table; > + int ret; > > if (write && !ns_capable(pid_ns->user_ns, CAP_SYS_ADMIN)) > return -EPERM; > @@ -298,7 +299,12 @@ static int pid_ns_ctl_handler(struct ctl_table > *table, int write, > */ > > tmp.data = &pid_ns->idr.idr_next; > - return proc_dointvec_minmax(&tmp, write, buffer, lenp, ppos); > + ret = proc_dointvec_minmax(&tmp, write, buffer, lenp, ppos); > + if (ret < 0) > + return ret; > + > + idr_set_cursor(&pid_ns->idr, pid_ns->idr.idr_next + 1); > + return 0; > } > > extern int pid_max; > > >> >> Thanks, >> Gargi >> > >> > Oleg. >> >
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