On 11/19, Paul E. McKenney wrote: > > On Mon, Nov 20, 2006 at 12:17:31AM +0300, Oleg Nesterov wrote: > > > > It will wait for xxx_read_unlock() on reader's side. And for this reason > > this idx in fact is not exactly wrong :) > > I am not seeing this. > > Let's assume sp->completed starts out zero. > > o CPU 0 starts executing xxx_read_lock(), but is interrupted > (or whatever) just before the atomic_inc(). Upon return, > it will increment sp->ctr[0].
Right. > o CPU 1 executes synchronize_xxx() to completion, which it > can because CPU 0 has not yet incremented the counter. > It waited on sp->ctr[0], and incremented sp->completed to 1. > > o CPU 0 returns from interrupt and completes xxx_read_lock(), > but has incremented sp->ctr[0]. > > o CPU 0 continues into its critical section, picking up a > pointer to an xxx-protected data structure (or, in Jens's > case starting an xxx-protected I/O). > > o CPU 1 executes another synchronize_xxx(). This completes > immediately because it is waiting for sp->ctr[1] to go > to zero, but CPU 0 incremented sp->ctr[0]. (Right?) Right! > o CPU 1 continues, either freeing a data structure while > CPU 0 is still referencing it, or, in Jens's case, completing > an I/O barrier while there is still outstanding I/O. > > Or am I missing something? No, it is me. Alan, Paul, thanks a lot for your patience! Oleg. - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
