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Date: Sun, 24 Apr 2016 23:26:41 -0700 From: Guenter Roeck <linux@...ck-us.net> To: paulmck@...ux.vnet.ibm.com Cc: Boqun Feng <boqun.feng@...il.com>, Josh Triplett <josh@...htriplett.org>, Steven Rostedt <rostedt@...dmis.org>, linux-kernel@...r.kernel.org Subject: Re: next: suspicious RCU usage message since commit 'rcu: Remove superfluous versions of rcu_read_lock_sched_held()' On 04/24/2016 10:49 PM, Paul E. McKenney wrote: > On Sun, Apr 24, 2016 at 10:37:25PM -0700, Guenter Roeck wrote: >> On 04/24/2016 10:28 PM, Paul E. McKenney wrote: >>> On Sun, Apr 24, 2016 at 04:56:38PM -0700, Guenter Roeck wrote: >>>> Hi Paul, >>>> >>>> On 04/24/2016 02:31 PM, Paul E. McKenney wrote: >>>>> On Sun, Apr 24, 2016 at 02:14:24PM -0700, Guenter Roeck wrote: >>>>>> Hi, >>>>>> >>>>>> I see the following log message when running a qemu test for 'beagle' >>>>>> with omap2plus_defconfig. >>>>>> >>>>>> =============================== >>>>>> [ INFO: suspicious RCU usage. ] >>>>>> 4.6.0-rc4-next-20160422 #1 Not tainted >>>>>> ------------------------------- >>>>>> include/trace/events/power.h:328 suspicious rcu_dereference_check() usage! >>>>>> >>>>>> other info that might help us debug this: >>>>>> >>>>>> RCU used illegally from idle CPU! >>>>>> rcu_scheduler_active = 1, debug_locks = 0 >>>>>> RCU used illegally from extended quiescent state! >>>>>> no locks held by swapper/0/0. >>>>>> >>>>>> stack backtrace: >>>>>> CPU: 0 PID: 0 Comm: swapper/0 Not tainted 4.6.0-rc4-next-20160422 #1 >>>>>> Hardware name: Generic OMAP3-GP (Flattened Device Tree) >>>>>> [<c010f55c>] (unwind_backtrace) from [<c010b64c>] (show_stack+0x10/0x14) >>>>>> [<c010b64c>] (show_stack) from [<c047acbc>] (dump_stack+0xa8/0xe0) >>>>>> [<c047acbc>] (dump_stack) from [<c012bc10>] (pwrdm_set_next_pwrst+0xf8/0x1cc) >>>>>> [<c012bc10>] (pwrdm_set_next_pwrst) from [<c01269fc>] (omap3_enter_idle_bm+0x1b8/0x1e8) >>>>>> [<c01269fc>] (omap3_enter_idle_bm) from [<c05fa0b8>] (cpuidle_enter_state+0x84/0x408) >>>>>> [<c05fa0b8>] (cpuidle_enter_state) from [<c0182c1c>] (cpu_startup_entry+0x1c8/0x3f0) >>>>>> [<c0182c1c>] (cpu_startup_entry) from [<c0b00c20>] (start_kernel+0x354/0x3cc) >>>>>> >>>>>> bisect points to commit 'rcu: Remove superfluous versions of >>>>>> rcu_read_lock_sched_held()'. Bisect log is attached. >>>>> >>>>> I believe that the real fix is not a revert of that commit, but rather >>>>> that some of the tracing statements need an "_rcuidle" suffix. >>>>> >>>>> Something like the following (untested, probably does not build) patch. >>>>> >>>>> Thanx, Paul >>>>> >>>>> ------------------------------------------------------------------------ >>>>> >>>>> commit ca91304178e1cf53ee391236a0ac3969cc814e5f >>>>> Author: Paul E. McKenney <paulmck@...ux.vnet.ibm.com> >>>>> Date: Sun Apr 24 14:30:16 2016 -0700 >>>>> >>>>> arm: Use _rcuidle tracepoint to allow use from idle >>>>> >>>>> Signed-off-by: Paul E. McKenney <paulmck@...ux.vnet.ibm.com> >>>>> >>>>> diff --git a/arch/arm/mach-omap2/powerdomain.c b/arch/arm/mach-omap2/powerdomain.c >>>>> index 78af6d8cf2e2..12b66b5bcc55 100644 >>>>> --- a/arch/arm/mach-omap2/powerdomain.c >>>>> +++ b/arch/arm/mach-omap2/powerdomain.c >>>>> @@ -523,8 +523,8 @@ int pwrdm_set_next_pwrst(struct powerdomain *pwrdm, u8 pwrst) >>>>> >>>>> if (arch_pwrdm && arch_pwrdm->pwrdm_set_next_pwrst) { >>>>> /* Trace the pwrdm desired target state */ >>>>> - trace_power_domain_target(pwrdm->name, pwrst, >>>>> - smp_processor_id()); >>>>> + trace_power_domain_target_rcuidle(pwrdm->name, pwrst, >>>>> + smp_processor_id()); >>>>> /* Program the pwrdm desired target state */ >>>>> ret = arch_pwrdm->pwrdm_set_next_pwrst(pwrdm, pwrst); >>>>> } >>>>> >>>> >>>> It does build. After applying it, I get a different traceback. >>>> >>>> [<c010f55c>] (unwind_backtrace) from [<c010b64c>] (show_stack+0x10/0x14) >>>> [<c010b64c>] (show_stack) from [<c047ac3c>] (dump_stack+0xa8/0xe0) >>>> [<c047ac3c>] (dump_stack) from [<c012c340>] (_pwrdm_state_switch+0x188/0x32c) >>>> [<c012c340>] (_pwrdm_state_switch) from [<c012c4f0>] (_pwrdm_post_transition_cb+0xc/0x14) >>>> [<c012c4f0>] (_pwrdm_post_transition_cb) from [<c012ba74>] (pwrdm_for_each+0x30/0x5c) >>>> [<c012ba74>] (pwrdm_for_each) from [<c012c72c>] (pwrdm_post_transition+0x24/0x30) >>>> [<c012c72c>] (pwrdm_post_transition) from [<c012548c>] (omap_sram_idle+0xfc/0x240) >>>> [<c012548c>] (omap_sram_idle) from [<c0126934>] (omap3_enter_idle_bm+0xf0/0x1e8) >>>> [<c0126934>] (omap3_enter_idle_bm) from [<c05fa038>] (cpuidle_enter_state+0x84/0x408) >>>> [<c05fa038>] (cpuidle_enter_state) from [<c0182b90>] (cpu_startup_entry+0x1c8/0x3f0) >>>> [<c0182b90>] (cpu_startup_entry) from [<c0b00c20>] (start_kernel+0x354/0x3cc) >>>> >>>> After making the same change in _pwrdm_state_switch(), the traceback is gone >>> >from my tests (beagle, beagle-xm, and overo-tobi). >>> >>> Very good! >>> >>> (And yes, you normally find these one at a time...) >>> >> Are you going to submit a formal patch ? > > I can, but please feel free to send mine along with yours, if you wish. > I think it would be best if you send a single patch which fixes both calls. Guenter
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