Messages in this thread | | | Subject | Re: [PATCH] lib/vsprintf: add %pT format specifier | From | Tetsuo Handa <> | Date | Sat, 11 Jan 2014 12:09:46 +0900 |
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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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