On Tue 2022-12-20 08:15:40, Christophe Leroy wrote:
>
>
> Le 20/12/2022 à 07:39, Zhen Lei a écrit :
> > [T58] BUG: sleeping function called from invalid context at kernel/kallsyms.c:305
> > [T58] in_atomic(): 0, irqs_disabled(): 128, non_block: 0, pid: 58, name: kallsyms_test
> > [T58] preempt_count: 0, expected: 0
> > [T58] RCU nest depth: 0, expected: 0
> > [T58] no locks held by kallsyms_test/58.
> > [T58] irq event stamp: 18899904
> > [T58] hardirqs last enabled at (18899903): finish_task_switch.isra.0 (core.c:?)
> > [T58] hardirqs last disabled at (18899904): test_perf_kallsyms_on_each_symbol (kallsyms_selftest.c:?)
> > [T58] softirqs last enabled at (18899886): __do_softirq (??:?)
> > [T58] softirqs last disabled at (18899879): ____do_softirq (irq.c:?)
> > [T58] CPU: 0 PID: 58 Comm: kallsyms_test Tainted: G T 6.1.0-next-20221215 #2
> > [T58] Hardware name: linux,dummy-virt (DT)
> > [T58] Call trace:
> > [T58] dump_backtrace (??:?)
> > [T58] show_stack (??:?)
> > [T58] dump_stack_lvl (??:?)
> > [T58] dump_stack (??:?)
> > [T58] __might_resched (??:?)
> > [T58] kallsyms_on_each_symbol (??:?)
> > [T58] test_perf_kallsyms_on_each_symbol (kallsyms_selftest.c:?)
> > [T58] test_entry (kallsyms_selftest.c:?)
> > [T58] kthread (kthread.c:?)
> > [T58] ret_from_fork (??:?)
> > [T58] kallsyms_selftest: kallsyms_on_each_symbol() traverse all: 5744310840 ns
> > [T58] kallsyms_selftest: kallsyms_on_each_match_symbol() traverse all: 1164580 ns
> > [T58] kallsyms_selftest: finish
> >
> > Functions kallsyms_on_each_symbol() and kallsyms_on_each_match_symbol()
> > call the user-registered hook function for each symbol that meets the
> > requirements. Because it is uncertain how long that hook function will
> > execute, they call cond_resched() to avoid consuming CPU resources for a
> > long time. However, irqs need to be disabled during the performance test
> > to ensure the accuracy of test data. Because the performance test hook is
> > very clear, very simple function, let's do not call cond_resched() when
> > CONFIG_KALLSYMS_SELFTEST=y.
>
> I don't think it is appropriate to change the behaviour of a core
> function based on whether a compile time option related to tests is
> selected or not, because you will change the behaviour for all users,
> not only for the tests.
I agree. This is very bad idea. It would change the behavior for
the entire system.
> If the problem is that IRQs are disabled, maybe the solution is
>
> if (!irqs_disabled())
> cond_resched();
>
> Or try to disable the call to cond_resched() in a way or another during
> the run of selftests.
If I get it correctly, the problem is this code in kernel/kallsyms_selftest.c:
static int lookup_name(void *data, const char *name, struct module *mod, unsigned long addr)
{
[...]
local_irq_save(flags);
t0 = sched_clock();
(void)kallsyms_lookup_name(name);
t1 = sched_clock();
local_irq_restore(flags);
[...]
and IRQs are disabled to measure the time spent in this function
without interruption and rescheduling.
I am sure that there are better ways how to measure the time.
Even the "time" command in userspace is able to show time how much CPU
time a command used.
I am not familiar with it. But task_cputime() in
kernel/sched/cputime.c looks promising. And there must be
the interface how the user space get this information.
Some is available via /proc/<PID>/... I am not sure
if there is a syscall.
Best Regards,
Petr
