[3.19.y-ckt stable] Patch "ARM64: smp: Fix suspicious RCU usage with ipi tracepoints" has been added to staging queue

[Kamal Mostafa]

This is a note to let you know that I have just added a patch titled

    ARM64: smp: Fix suspicious RCU usage with ipi tracepoints

to the linux-3.19.y-queue branch of the 3.19.y-ckt extended stable tree 
which can be found at:

    http://kernel.ubuntu.com/git/ubuntu/linux.git/log/?h=linux-3.19.y-queue

This patch is scheduled to be released in version 3.19.y-ckt4.

If you, or anyone else, feels it should not be added to this tree, please 
reply to this email.

For more information about the 3.19.y-ckt tree, see
https://wiki.ubuntu.com/Kernel/Dev/ExtendedStable

Thanks.
-Kamal

------

>From 1257416c4ec2e663a4eaa39f54bc6b822445d9e0 Mon Sep 17 00:00:00 2001
From: Stephen Boyd <sboyd at codeaurora.org>
Date: Wed, 24 Jun 2015 13:14:18 -0700
Subject: ARM64: smp: Fix suspicious RCU usage with ipi tracepoints

commit be081d9bf3e163a9ed1ca2f0f14f08424c7f9016 upstream.

John Stultz reported an RCU splat on ARM with ipi trace events
enabled. It looks like the same problem exists on ARM64.

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.

Cc: John Stultz <john.stultz at linaro.org>
Cc: Nicolas Pitre <nicolas.pitre at linaro.org>
Acked-by: Steven Rostedt <rostedt at goodmis.org>
Reviewed-by: Paul E. McKenney <paulmck at linux.vnet.ibm.com>
Fixes: 45ed695ac10a ("ARM64: add IPI tracepoints")
Signed-off-by: Stephen Boyd <sboyd at codeaurora.org>
Signed-off-by: Catalin Marinas <catalin.marinas at arm.com>
Signed-off-by: Kamal Mostafa <kamal at canonical.com>
---
 arch/arm64/kernel/smp.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/arch/arm64/kernel/smp.c b/arch/arm64/kernel/smp.c
index e1b857f..c132df4 100644
--- a/arch/arm64/kernel/smp.c
+++ b/arch/arm64/kernel/smp.c
@@ -570,7 +570,7 @@ 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]);
 	}

@@ -619,7 +619,7 @@ 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);
 }

--
1.9.1