Hi, Paul, On Sat, Apr 16, 2011 at 1:44 AM, Mathieu Desnoyers <mathieu.desnoyers@xxxxxxxxxxxx> wrote: > * Paul E. McKenney (paulmck@xxxxxxxxxxxxxxxxxx) wrote: >> On Fri, Apr 15, 2011 at 12:46:29PM -0400, Mathieu Desnoyers wrote: >> > * Huang Ying (ying.huang@xxxxxxxxx) wrote: >> > > On 04/14/2011 05:07 AM, Mathieu Desnoyers wrote: >> > > > * Huang Ying (ying.huang@xxxxxxxxx) wrote: >> > > > [...] >> > > >> + * rcu_read_lock and rcu_read_unlock is not used int gen_pool_alloc, >> > > >> + * gen_pool_free, gen_pool_avail and gen_pool_size etc, because chunks >> > > >> + * are only added into pool, not deleted from pool unless the pool >> > > >> + * itself is destroyed. ÂIf chunk will be deleted from pool, >> > > >> + * rcu_read_lock and rcu_read_unlock should be uses in these >> > > >> + * functions. >> > > > >> > > > So how do you protect between pool destruction and adding chunks into >> > > > the pool ? >> > > >> > > Because the pool itself will be freed when destruction, we need some >> > > mechanism outside of pool. ÂFor example, if gen_pool_add() is called via >> > > device file IOCTL, we must un-register the device file first, and >> > > destroy the pool after the last reference to device has gone. >> > >> > I am concerned about the list_for_each_entry_rcu() (and thus >> > rcu_dereference_raw()) used outside of rcu_read_lock/unlock pairs. >> > Validation infrastructure as recently been added to RCU: it triggers >> > warnings when these situations are encountered in some RCU debugging >> > configurations. The case of RCU list iteration is not covered by the >> > checks, but it would make sense to be aware of it. >> > >> > So although it seems like your code does not require rcu read lock >> > critical sections, I'd prefer to let Paul McKenney have a look. >> >> As long as you add elements and never remove them, then you can get >> away with using list_for_each_entry_rcu() outside of an RCU read-side >> critical section. ÂBut please comment this -- it is all too easy >> for someone to decide later to start deleting elements without also >> inserting the needed rcu_read_lock() and rcu_read_unlock() pairs. >> >> But I have lost the thread -- what code am I supposed to look at? > > You can have a look at https://lkml.org/lkml/2011/4/13/56 What do you think about this patch and its usage of RCU? Best Regards, Huang Ying -- To unsubscribe from this list: send the line "unsubscribe linux-acpi" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
