On 17/09/2015 18:27, Dominik Dingel wrote: > + preempt_disable(); > + solo = single_task_running(); > + preempt_enable(); > + > cur = ktime_get(); > - } while (single_task_running() && ktime_before(cur, stop)); That's the obvious way to fix it, but the TOCTTOU problem (which was in the buggy code too) is obvious too. :) And the only other user of single_task_running() in drivers/crypto/mcryptd.c has the same issue. In fact, because of the way the function is used ("maybe I can do a little bit of work before going to sleep") it will likely be called many times in a loop. This in turn means that: - any wrong result due to a concurrent process migration would be rectified very soon - preempt_disable()/preempt_enable() can actually be just as expensive or more expensive than single_task_running() itself. Therefore, I wonder if single_task_running() should just use raw_smp_processor_id(). At least the TOCTTOU issue can be clearly documented in the function comment, instead of being hidden behind each of the callers. Thanks, Paolo -- To unsubscribe from this list: send the line "unsubscribe linux-crypto" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html