Messages in this thread | | | Date | Fri, 19 Jun 2015 11:49:55 -0700 | From | Stephen Boyd <> | Subject | Re: Suspicious RCU usage at boot w/ arm ipi trace events? |
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On 06/18, John Stultz wrote: > On Wed, Jun 17, 2015 at 6:49 PM, Stephen Boyd <sboyd@codeaurora.org> wrote: > > On 06/16/2015 09:46 PM, Paul E. McKenney wrote: > >> On Tue, Jun 16, 2015 at 05:41:29PM -0700, Stephen Boyd wrote: > >>> > >>> The tracepoint 'trace_ipi_entry' in handle_IPI() is using RCU and we > >>> haven't called irq_enter() yet at the point. Does this tracepoint need > >>> to have _rcuidle() added to it? > >> Yes, I believe that would fix this problem. > >> > > > > Ok... here's the patch. I see the problem on my device and applying this > > patch fixes it. > > > > ----8<---- > > > > From: Stephen Boyd <sboyd@codeaurora.org> > > Subject: [PATCH] ARM: smp: Silence suspicious RCU usage with ipi tracepoints > > > > John Stultz reports an RCU splat on boot with ARM ipi trace > > events enabled. > > > > =============================== > > [ INFO: suspicious RCU usage. ] > > 4.1.0-rc7-00033-gb5bed2f #153 Not tainted > > ------------------------------- > > include/trace/events/ipi.h:68 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 4.1.0-rc7-00033-gb5bed2f #153 > > Hardware name: Qualcomm (Flattened Device Tree) > > [<c0216b08>] (unwind_backtrace) from [<c02136e8>] (show_stack+0x10/0x14) > > [<c02136e8>] (show_stack) from [<c075e678>] (dump_stack+0x70/0xbc) > > [<c075e678>] (dump_stack) from [<c0215a80>] (handle_IPI+0x428/0x604) > > [<c0215a80>] (handle_IPI) from [<c020942c>] (gic_handle_irq+0x54/0x5c) > > [<c020942c>] (gic_handle_irq) from [<c0766604>] (__irq_svc+0x44/0x7c) > > Exception stack(0xc09f3f48 to 0xc09f3f90) > > 3f40: 00000001 00000001 00000000 c09f73b8 c09f4528 c0a5de9c > > 3f60: c076b4f0 00000000 00000000 c09ef108 c0a5cec1 00000001 00000000 c09f3f90 > > 3f80: c026bf60 c0210ab8 20000113 ffffffff > > [<c0766604>] (__irq_svc) from [<c0210ab8>] (arch_cpu_idle+0x20/0x3c) > > [<c0210ab8>] (arch_cpu_idle) from [<c02647f0>] (cpu_startup_entry+0x2c0/0x5dc) > > [<c02647f0>] (cpu_startup_entry) from [<c099bc1c>] (start_kernel+0x358/0x3c4) > > [<c099bc1c>] (start_kernel) from [<8020807c>] (0x8020807c) > > > > At this point in the IPI handling path we haven't called > > irq_enter() yet, so RCU doesn't know that we're about to exit > > idle and properly warns that we're using RCU from an idle CPU. > > Use trace_ipi_entry_rcuidle() instead of trace_ipi_entry() so > > that RCU is informed about our exit from idle. > > > > Reported-by: John Stultz <john.stultz@linaro.org> > > Fixes: 365ec7b17327 "ARM: add IPI tracepoints" > > Signed-off-by: Stephen Boyd <sboyd@codeaurora.org> > > --- > > arch/arm/kernel/smp.c | 4 ++-- > > 1 file changed, 2 insertions(+), 2 deletions(-) > > > > diff --git a/arch/arm/kernel/smp.c b/arch/arm/kernel/smp.c > > index 13a91d390832..03eb8a446dca 100644 > > --- a/arch/arm/kernel/smp.c > > +++ b/arch/arm/kernel/smp.c > > @@ -589,7 +589,7 @@ void handle_IPI(int ipinr, struct pt_regs *regs) > > struct pt_regs *old_regs = set_irq_regs(regs); > > > > if ((unsigned)ipinr < NR_IPI) { > > - trace_ipi_entry(ipi_types[ipinr]); > > + trace_ipi_entry_rcuidle(ipi_types[ipinr]); > > __inc_irq_stat(cpu, ipi_irqs[ipinr]); > > } > > > > @@ -648,7 +648,7 @@ void handle_IPI(int ipinr, struct pt_regs *regs) > > } > > > > if ((unsigned)ipinr < NR_IPI) > > - trace_ipi_exit(ipi_types[ipinr]); > > + trace_ipi_exit_rcuidle(ipi_types[ipinr]); > > set_irq_regs(old_regs); > > } > > > > Tested-by: John Stultz <john.stultz@linaro.org> > > Thanks for fixing this up!
Thanks. I'll throw it into the patch tracker. I'll send the same patch for arm64 because I assume it's also broken there.
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