Messages in this thread | | | Subject | Re: [PATCH] kallsyms: Fix sleeping function called from invalid context when CONFIG_KALLSYMS_SELFTEST=y | From | "Leizhen (ThunderTown)" <> | Date | Tue, 20 Dec 2022 22:29:31 +0800 |
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On 2022/12/20 19:01, Petr Mladek wrote: > 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.
It just doesn't look so good, but it doesn't affect the entire system, and the proposed changes below will.
> >> If the problem is that IRQs are disabled, maybe the solution is >> >> if (!irqs_disabled()) >> cond_resched();
If irqs is disabled by the upper layer, this error cannot be easily detected.
>> >> 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:
Yes, another method is to remove the interrupt protection.
> > 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've got an idea:
local_irq_save(flags); //get the count and cputime of interrupts t0 = sched_clock(); local_irq_restore(flags);
(void)kallsyms_lookup_name(name);
local_irq_save(flags); t1 = sched_clock(); //get the count and cputime of interrupts local_irq_restore(flags);
minus the cputime of local_irq_save(flags)/local_irq_restore(flags)
if count changed, minus the cputime of interrupts
> > 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 > . >
-- Regards, Zhen Lei
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