On Thu, 2011-04-28 at 16:48 -0700, john stultz wrote: > On Thu, 2011-04-28 at 15:48 -0700, David Rientjes wrote: > > On Wed, 27 Apr 2011, john stultz wrote: > > > > > So thinking further, this can be simplified by adding the seqlock first, > > > and then retaining the task_locking only in the set_task_comm path until > > > all comm accessors are converted to using get_task_comm. > > > > > > > On second thought, I think it would be better to just retain using a > > spinlock but instead of using alloc_lock, introduce a new spinlock to > > task_struct for the sole purpose of protecting comm. > > > > And, instead, of using get_task_comm() to write into a preallocated > > buffer, I think it would be easier in the vast majority of cases that > > you'll need to convert to just provide task_comm_lock(p) and > > task_comm_unlock(p) so that p->comm can be dereferenced safely. Ok.. trying to find a middle ground here by replying to my own concerns. :) > So my concern with this is that it means one more lock that could be > mis-nested. By keeping the locking isolated to the get/set_task_comm, we > can be sure that won't happen. > > Also tracking new current->comm references will be easier if we just > don't allow new ones. Validating that all the comm references are > correctly locked becomes more difficult if we need locking at each use > site. So maybe we still ban current->comm access and instead have a lightweight get_comm_locked() accessor or something that. Then we can add debugging options to validate that the lock is properly held internally. > Further, since I'm not convinced that we never reference current->comm > from irq context, if we go with spinlocks, we're going to have to > disable irqs in the read path as well. seqlocks were nice for that > aspect. rwlocks can resolve this concern. Any other thoughts? -john -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxxx For more info on Linux MM, see: http://www.linux-mm.org/ . Fight unfair telecom internet charges in Canada: sign http://stopthemeter.ca/ Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>