Messages in this thread | | | From | Oliver Neukum <> | Subject | Re: [RFC] Race condition? | Date | Fri, 2 Aug 2002 19:41:38 +0200 |
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Am Freitag, 2. August 2002 19:00 schrieb Dave Hansen: > Kasper Dupont wrote: > > Is there a race condition in this piece of code from do_fork in > > linux/kernel/fork.c? I cannot see what prevents two processes > > from calling this at the same time and both successfully fork > > even though the user had only one process left. > > > > if (atomic_read(&p->user->processes) >= > > p->rlim[RLIMIT_NPROC].rlim_cur && !capable(CAP_SYS_ADMIN) && > > !capable(CAP_SYS_RESOURCE)) goto bad_fork_free; > > > > atomic_inc(&p->user->__count); > > atomic_inc(&p->user->processes); > > I don't see any locking in the call chain leading to this function, so > I think you're right. The attached patch fixes this. It costs an > extra 2 atomic ops in the failure case, but otherwise just makes the > processes++ operation earlier. > > Patch is against 2.5.27, but applies against 30.
It has the opposite failure mode. Forks only some of which should succeed may all fail.
Regards Oliver
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