Messages in this thread | | | Date | Thu, 15 Apr 2021 10:42:54 -0400 | From | Johannes Weiner <> | Subject | Re: [PATCH] sched,psi: fix the 'int' underflow for psi |
| |
On Thu, Apr 15, 2021 at 07:59:41PM +0530, Charan Teja Reddy wrote: > psi_group_cpu->tasks, represented by the unsigned int, stores the number > of tasks that could be stalled on a psi resource(io/mem/cpu). > Decrementing these counters at zero leads to wrapping which further > leads to the psi_group_cpu->state_mask is being set with the respective > pressure state. This could result into the unnecessary time sampling for > the pressure state thus cause the spurious psi events. This can further > lead to wrong actions being taken at the user land based on these psi > events. > Though psi_bug is set under these conditions but that just for debug > purpose. Fix it by decrementing the ->tasks count only when it is > non-zero.
Makes sense, it's more graceful in the event of a bug.
But what motivates this change? Is it something you hit recently with an upstream kernel and we should investigate?
> Signed-off-by: Charan Teja Reddy <charante@codeaurora.org> > --- > kernel/sched/psi.c | 3 ++- > 1 file changed, 2 insertions(+), 1 deletion(-) > > diff --git a/kernel/sched/psi.c b/kernel/sched/psi.c > index 967732c..f925468 100644 > --- a/kernel/sched/psi.c > +++ b/kernel/sched/psi.c > @@ -718,7 +718,8 @@ static void psi_group_change(struct psi_group *group, int cpu, > groupc->tasks[3], clear, set); > psi_bug = 1; > } > - groupc->tasks[t]--; > + if (groupc->tasks[t]) > + groupc->tasks[t]--;
There is already a branch on the tasks to signal the bug. How about:
if (groupc->tasksk[t]) { groupc->tasks[t]--; } else if (!psi_bug) { printk_deferred(... psi_bug = 1; }
| |