Andrew Morton wrote:
> In the absence of step 3, steps 1 and 2 are rather pointless churn.
>
> So I think it would be better to merge (into mainline) steps 1 and 3
> first and at the same time. Then start thinking about step 2.
Unfortunately we can't.
Step 2 depends on step 1 for avoiding compile time errors.
Step 3 depends on step 2 for avoiding run time errors.
Step 1: (targeted to 3.14-rc1)
Add "%pT" format specifier and commcpy() wrapper function.
Step 2: (started after step 1 is reflected to other git trees)
Replace printk("%s", current->comm) with printk("%pT", NULL).
Replace printk("%s", p->comm) with printk("%pT", p).
Replace strcpy(buf, p->comm) with commcpy(buf, p).
Step 3: (started after step 2 is reflected to other git trees)
Add rcu_read_lock()/rcu_read_unlock() into commcpy().
Modify set_task_comm() etc. to replace ->comm using RCU.
If step 3 is merged into mainline before step 2 complete, those who are not
using "%pT" or commcpy() might crash due to reading RCU protected ->comm
without rcu_read_lock()/rcu_read_unlock().
Let me confirm, Paul.
I'm trying to change task_struct->comm to use RCU.
At step 3, I'm planning to do
static inline void *commcpy(void *buf, const struct task_struct *tsk)
{
rcu_read_lock();
memcpy(buf, tsk->comm, TASK_COMM_LEN);
rcu_read_unlock();
return buf;
}
and let set_task_comm() wait for readers using synchronize_rcu() or
call_rcu().
Given that commcpy() can be called from any context, are synchronize_rcu()
and call_rcu() sufficient for waiting for commcpy() users?
Regards.
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