linux-kernel - [tip:timers/urgent] tick/broadcast: Prevent hrtimer recursion

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Date:	Tue, 7 Jul 2015 10:12:34 -0700
From:	tip-bot for Thomas Gleixner <tipbot@...or.com>
To:	linux-tip-commits@...r.kernel.org
Cc:	Suzuki.Poulose@....com, preeti@...ux.vnet.ibm.com, hpa@...or.com,
	tglx@...utronix.de, sudeep.holla@....com, peterz@...radead.org,
	Catalin.Marinas@....com, mingo@...nel.org,
	Lorenzo.Pieralisi@....com, rafael.j.wysocki@...el.com,
	linux-kernel@...r.kernel.org
Subject: [tip:timers/urgent] tick/broadcast: Prevent hrtimer recursion

Commit-ID:  8eb231261fdd20768db23863d00ef277de4b0543
Gitweb:     http://git.kernel.org/tip/8eb231261fdd20768db23863d00ef277de4b0543
Author:     Thomas Gleixner <tglx@...utronix.de>
AuthorDate: Tue, 7 Jul 2015 14:11:00 +0200
Committer:  Thomas Gleixner <tglx@...utronix.de>
CommitDate: Tue, 7 Jul 2015 18:46:47 +0200

tick/broadcast: Prevent hrtimer recursion

The hrtimer based broadcast vehicle can cause a hrtimer recursion
which went unnoticed until we changed the hrtimer expiry code to keep
track of the currently running timer.

local_timer_interrupt()
  local_handler()
    hrtimer_interrupt()
      expire_hrtimers()
        broadcast_hrtimer()
	  send_ipis()
	  local_handler()
	    hrtimer_interrupt()
	     ....

Solution is simple: Prevent the local handler call from the broadcast
code when the broadcast 'device' is hrtimer based.

[ Split out from a larger combo patch ]

Tested-by: Sudeep Holla <sudeep.holla@....com>
Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
Cc: Suzuki Poulose <Suzuki.Poulose@....com>
Cc: Lorenzo Pieralisi <Lorenzo.Pieralisi@....com>
Cc: Catalin Marinas <Catalin.Marinas@....com>
Cc: Rafael J. Wysocki <rafael.j.wysocki@...el.com>
Cc: Peter Zijlstra <peterz@...radead.org>
Cc: Preeti U Murthy <preeti@...ux.vnet.ibm.com>
Cc: Ingo Molnar <mingo@...nel.org>
Link: http://lkml.kernel.org/r/alpine.DEB.2.11.1507070929360.3916@nanos
---
 kernel/time/tick-broadcast.c | 16 +++++++++++++++-
 1 file changed, 15 insertions(+), 1 deletion(-)

diff --git a/kernel/time/tick-broadcast.c b/kernel/time/tick-broadcast.c
index d39f32c..a762040 100644
--- a/kernel/time/tick-broadcast.c
+++ b/kernel/time/tick-broadcast.c
@@ -265,8 +265,22 @@ static bool tick_do_broadcast(struct cpumask *mask)
 	 * Check, if the current cpu is in the mask
 	 */
 	if (cpumask_test_cpu(cpu, mask)) {
+		struct clock_event_device *bc = tick_broadcast_device.evtdev;
+
 		cpumask_clear_cpu(cpu, mask);
-		local = true;
+		/*
+		 * We only run the local handler, if the broadcast
+		 * device is not hrtimer based. Otherwise we run into
+		 * a hrtimer recursion.
+		 *
+		 * local timer_interrupt()
+		 *   local_handler()
+		 *     expire_hrtimers()
+		 *       bc_handler()
+		 *         local_handler()
+		 *	     expire_hrtimers()
+		 */
+		local = !(bc->features & CLOCK_EVT_FEAT_HRTIMER);
 	}
 
 	if (!cpumask_empty(mask)) {
--
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