Messages in this thread | | | Date | Wed, 2 Sep 2009 23:51:01 +0200 | From | Oleg Nesterov <> | Subject | Re: [PATCH 2/2] core: allow setrlimit to non-current tasks |
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On 09/02, Jiri Slaby wrote: > > On 09/02/2009 03:50 PM, Oleg Nesterov wrote: > > But there is another minor problem. If we use read_lock(ttasklist), then > > the write to /proc/application_pid/limits can race with application doing > > sys_setrlimits(). > > > > Nothing bad can happen, but this means that "echo ... > /proc/limits" can > > be lost. Not good, if admin wants to lower ->rlim_max we should try to ensure > > this always works. > > Actually, process cpu timer may be set to a wrong value. When
Yes, I thought about this too. In fact I was going to complain, but then decided this is OK.
> * somebody unrelated holds sighand->siglock > * process one stores rlim_new to rlim and gets stuck on spin_lock(siglock) > * process two does the same
s/process/thread/. (I am talking about the current code). IOW, if the application is stupid and does setrlimit() from multimple threads at the same time - we can't help, the result is not predictable.
But, unless I missed something I think this case is fine, please see below.
> * somebody releases sighand->siglock > * process one continues...
Now, it is possible that cputime_expires.xxx_exp does not match ->rlim[RLIMIT_CPU].rlim_cur.
But we don't care. update_rlimit_cpu() must ensure that cputime_expires.xxx_exp is not greater than necessary, nothing else.
> I can't think of anything else than doing all the checks and updates > under alloc_lock, introducing coarse grained static mutex in setrlimit > to protect it,
Oh, please don't ;)
Or I missed your point?
But if you mean this series, then yes, I agree. We should try to do something to ensure that at least rlim_max can be always lowered when admin writes to /proc/pid/limits.
Oleg.
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