On Sun, Aug 27, 2023 at 1:51 AM Huacai Chen <chenhuacai@xxxxxxxxxx> wrote: [..] > > > > > The only way I know of to avoid these sorts of false positives is for > > > > > the user to manually suppress all timeouts (perhaps using a kernel-boot > > > > > parameter for your early-boot case), do the gdb work, and then unsuppress > > > > > all stalls. Even that won't work for networking, because the other > > > > > system's clock will be running throughout. > > > > > > > > > > In other words, from what I know now, there is no perfect solution. > > > > > Therefore, there are sharp limits to the complexity of any solution that > > > > > I will be willing to accept. > > > > I think the simplest solution is (I hope Joel will not angry): > > > > > > Not angry at all, just want to help. ;-). The problem is the 300*HZ solution > > > will also effect the VM workloads which also do a similar reset. Allow me few > > > days to see if I can take a shot at fixing it slightly differently. I am > > > trying Paul's idea of setting jiffies at a later time. I think it is doable. > > > I think the advantage of doing this is it will make stall detection more > > > robust in this face of these gaps in jiffie update. And that solution does > > > not even need us to rely on ktime (and all the issues that come with that). > > > > > > > I wrote a patch similar to Paul's idea and sent it out for review, the > > advantage being it purely is based on jiffies. Could you try it out > > and let me know? > If you can cc my gmail <chenhuacai@xxxxxxxxx>, that could be better. Sure, will do. > > I have read your patch, maybe the counter (nr_fqs_jiffies_stall) > should be atomic_t and we should use atomic operation to decrement its > value. Because rcu_gp_fqs() can be run concurrently, and we may miss > the (nr_fqs == 1) condition. I don't think so. There is only 1 place where RMW operation happens and rcu_gp_fqs() is called only from the GP kthread. So a concurrent RMW (and hence a lost update) is not possible. Could you test the patch for the issue you are seeing and provide your Tested-by tag? Thanks, - Joel
