On Fri, Oct 22, 2021 at 05:54:31PM +0100, Mark Rutland wrote: > > Pardon my thin understanding of the scheduler, but I assume this change > > doesn't mean stack_trace_save_tsk() stops working for "current", right? > > In trying to answer this for myself, I couldn't convince myself what value > > current->__state have here. Is it one of TASK_(UN)INTERRUPTIBLE ? > > Regardless of that, current->on_rq will be non-zero, so you're right that this > causes stack_trace_save_tsk() to not work for current, e.g. > > | # cat /proc/self/stack > | # wc /proc/self/stack > | 0 0 0 /proc/self/stack > > TBH, I think that (taking a step back from this issue in particular) > stack_trace_save_tsk() *shouldn't* work for current, and callers *should* be > forced to explicitly handle current separately from blocked tasks. That.. > > So we could fix this in the stacktrace code with: > > | diff --git a/kernel/stacktrace.c b/kernel/stacktrace.c > | index a1cdbf8c3ef8..327af9ff2c55 100644 > | --- a/kernel/stacktrace.c > | +++ b/kernel/stacktrace.c > | @@ -149,7 +149,10 @@ unsigned int stack_trace_save_tsk(struct task_struct *tsk, unsigned long *store, > | .skip = skipnr + (current == tsk), > | }; > | > | - task_try_func(tsk, try_arch_stack_walk_tsk, &c); > | + if (tsk == current) > | + try_arch_stack_walk_tsk(tsk, &c); > | + else > | + task_try_func(tsk, try_arch_stack_walk_tsk, &c); > | > | return c.len; > | } > > ... and we could rename task_try_func() to blocked_task_try_func(), and > later push the distinction into higher-level callers. I think I favour this fix if we have to. But that's for next week :-)
