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 <paul...@linux.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 <paul...@linux.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. Either way, please let me know. Thanx, Paul