* Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> wrote: > On Fri, 30 Jan 2009 16:33:53 +1030 Rusty Russell <rusty@xxxxxxxxxxxxxxx> wrote: > > > On Thursday 29 January 2009 12:42:05 Andrew Morton wrote: > > > On Thu, 29 Jan 2009 12:13:32 +1030 Rusty Russell <rusty@xxxxxxxxxxxxxxx> wrote: > > > > > > > On Thursday 29 January 2009 06:14:40 Andrew Morton wrote: > > > > > It's vulnerable to the same deadlock, I think? Suppose we have: > > > > ... > > > > > - A calls work_on_cpu() and takes woc_mutex. > > > > > > > > > > - Before function_which_takes_L() has started to execute, task B takes L > > > > > then calls work_on_cpu() and task B blocks on woc_mutex. > > > > > > > > > > - Now function_which_takes_L() runs, and blocks on L > > > > > > > > Agreed, but now it's a fairly simple case. Both sides have to take lock L, and both have to call work_on_cpu. > > > > > > > > Workqueues are more generic and widespread, and an amazing amount of stuff gets called from them. That's why I felt uncomfortable with removing the one known problematic caller. > > > > > > > > > > hm. it's a bit of a timebomb. > > > > > > y'know, the original way in which acpi-cpufreq did this is starting to > > > look attractive. Migrate self to that CPU then just call the dang > > > function. Slow, but no deadlocks (I think)? > > > > Just buggy. What random thread was it mugging? If there's any path > > where it's not a kthread, what if userspace does the same thing at the > > same time? We risk running on the wrong cpu, *then* overriding > > userspace when we restore it. > > hm, Ok, not unficable but not pleasant. > > > In general these cpumask games are a bad idea. > > So we still don't have any non-buggy proposal. Current upstream code is not pretty (due to the extra workqueue) but not buggy either. You'd be right to point out that it is easy to insert a bug into it and thus it's not pleasant (more of a workaround than a real fix) but if it's outright buggy then please talk up. Ingo -- To unsubscribe from this list: send the line "unsubscribe cpufreq" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
