Messages in this thread | | | From | (Eric W. Biederman) | Subject | Re: [PATCH 5/7] pid: Implement pid_nr | Date | Wed, 16 Aug 2006 10:18:20 -0600 |
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Oleg Nesterov <oleg@tv-sign.ru> writes:
> On 08/15, Eric W. Biederman wrote: >> >> +static inline pid_t pid_nr(struct pid *pid) >> +{ >> + pid_t nr = 0; >> + if (pid) >> + nr = pid->nr; >> + return nr; >> +} > > I think this is not safe, you need rcu locks here or the caller should > do some locking. > > Let's look at f_getown() (PATCH 7/7). What if original task which was > pointed by ->f_owner.pid has gone, another thread does fcntl(F_SETOWN), > and pid_nr() takes a preemtion after 'if (pid)'? In this case 'pid->nr' > may follow a freed memory.
This isn't an rcu reference. I hold a hard reference count on the pid entry. So this should be safe.
What is an rcu reference is going from struct pid to the task it points to.
Eric
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