On 2015-10-12 10:10, Gilles Chanteperdrix wrote: > On Mon, Oct 12, 2015 at 09:23:46AM +0200, Jan Kiszka wrote: >> On 2015-10-11 15:05, Gilles Chanteperdrix wrote: >>> Hi, >>> >>> It seems commit fdb5d54d04b8c3b6b6a6ad7ac2b6248cf0b415e0 in the >>> I-pipe kernels cause a warning when CONFIG_PREEMPT_VOLUNTARY and >>> CONFIG_IPIPE_DEBUG_INTERNAL are enabled. The culprit is the call to >>> __ipipe_root_p. >> >> Compiler warning? Runtime warning? Which architecture? I assume that >> ftrace is on then, right? > > Yes. Because preempt_disable()/preempt_enable*() is a nop without > CONFIG_PREEMPT_COUNT, __ipipe_root_p ends up being called without > any protection, and __ipipe_check_percpu_access() emits the warning. >
Makes sense. >> >>> >>> The following patch avoids this warning: >> >> How? > > It disables the test for preemption (the call to preempt_count()) in > __ipipe_check_percpu_access() if CONFIG_PREEMPT_COUNT is disabled, > because if it is disabled, you can not be preempted anywhere, so > calling __ipipe_root_p without protection is valid. Or maybe not? Ah, ok. I was under the assumption preempt_count() would return a constant non-zero value under !CONFIG_PREEMPT. But on the other hand, that would be weird as well when triggering voluntary preemption then. Anyway, it's correct that preemption cannot happen then in the middle of an instruction, so we can skip the test. Please make the test depend on CONFIG_PREEMPT and leave a corresponding comment in the code. Thanks, Jan -- Siemens AG, Corporate Technology, CT RTC ITP SES-DE Corporate Competence Center Embedded Linux _______________________________________________ Xenomai mailing list [email protected] http://xenomai.org/mailman/listinfo/xenomai
