Andrew Morton wrote:
>
> What about this code?
>
> void ipc_rcu_free(void* ptr, int size)
> {
> struct rcu_ipc_free* arg;
>
> arg = (struct rcu_ipc_free *) kmalloc(sizeof(*arg), GFP_KERNEL);
> if (arg == NULL)
> return;
> arg->ptr = ptr;
> arg->size = size;
> call_rcu(&arg->rcu_head, ipc_free_callback, arg);
> }
>
> Are we sure that it's never called under locks?
Did you see any place where this is called with lock(s) hold? Maybe
there is, but I could not see here. They are called from the functions
which are used by IPC code only. Inside IPC there is only spin_lock per
ID and sem_undo lock. Both of them are not hold when ipc_rcu_free is
called.
>
> And it seems that if the kmalloc fails, we decide to leak some
> memory, yes?
>
yes.
> If so it would be better to use GFP_ATOMIC there. Avoids any
> locking problems and also increases the chance of the allocation
> succeeding. (With an explanatory comment, naturally :)).
>
Good point. I agree GFP_ATOMIC fits better here.
> Even better: is it possible to embed the rcu_ipc_free inside the
> object-to-be-freed? Perhaps not?
Are you saying that have a static RCU header structure in the
object-to-be-freed? I think it's possible. It fits well in the rmid
case, where the object to be freed is an kern_ipc_perm structure. But
for the grow_ary() case, the object to be freed is a array of struct
ipc_id, so it need a little bit more changes there. Maybe add a new
structure ipc_entries, which include the RCU header structure and the
pointer to the entries array. Then have the ipc_ids->entries point to
ipc_entries. Just a little concern that this way we added a reference
when looking up the IPC ID from the array.
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This archive was generated by hypermail 2b29 : Thu Oct 31 2002 - 22:00:25 EST