clocksource: cadence_ttc: Fix mutex taken inside interrupt context

When the kernel is compiled with:
CONFIG_HIGH_RES_TIMERS=no
CONFIG_HZ_PERIODIC=yes
CONFIG_DEBUG_ATOMIC_SLEEP=yes

The following WARN appears:

WARNING: CPU: 1 PID: 0 at linux/kernel/mutex.c:856 mutex_trylock+0x70/0x1fc()
DEBUG_LOCKS_WARN_ON(in_interrupt())
Modules linked in:
CPU: 1 PID: 0 Comm: swapper/1 Not tainted 3.12.0-xilinx-dirty #93
[<c0014a78>] (unwind_backtrace+0x0/0x11c) from [<c0011b6c>] (show_stack+0x10/0x14)
[<c0011b6c>] (show_stack+0x10/0x14) from [<c039120c>] (dump_stack+0x7c/0xc0)
[<c039120c>] (dump_stack+0x7c/0xc0) from [<c001fda4>] (warn_slowpath_common+0x60/0x84)
[<c001fda4>] (warn_slowpath_common+0x60/0x84) from [<c001fe48>] (warn_slowpath_fmt+0x2c/0x3c)
[<c001fe48>] (warn_slowpath_fmt+0x2c/0x3c) from [<c0392658>] (mutex_trylock+0x70/0x1fc)
[<c0392658>] (mutex_trylock+0x70/0x1fc) from [<c02dfc08>] (clk_prepare_lock+0xc/0xe4)
[<c02dfc08>] (clk_prepare_lock+0xc/0xe4) from [<c02e099c>] (clk_get_rate+0xc/0x44)
[<c02e099c>] (clk_get_rate+0xc/0x44) from [<c02d0394>] (ttc_set_mode+0x34/0x78)
[<c02d0394>] (ttc_set_mode+0x34/0x78) from [<c005f794>] (clockevents_set_mode+0x28/0x5c)
[<c005f794>] (clockevents_set_mode+0x28/0x5c) from [<c00607fc>] (tick_broadcast_on_off+0x190/0x1c0)
[<c00607fc>] (tick_broadcast_on_off+0x190/0x1c0) from [<c005f168>] (clockevents_notify+0x58/0x1ac)
[<c005f168>] (clockevents_notify+0x58/0x1ac) from [<c02b99dc>] (cpuidle_setup_broadcast_timer+0x20/0x24)
[<c02b99dc>] (cpuidle_setup_broadcast_timer+0x20/0x24) from [<c006cd04>] (generic_smp_call_function_single_interrupt+0)
[<c006cd04>] (generic_smp_call_function_single_interrupt+0xe0/0x130) from [<c00138c8>] (handle_IPI+0x88/0x118)
[<c00138c8>] (handle_IPI+0x88/0x118) from [<c0008504>] (gic_handle_irq+0x58/0x60)
[<c0008504>] (gic_handle_irq+0x58/0x60) from [<c0012644>] (__irq_svc+0x44/0x78)
Exception stack(0xef099fa0 to 0xef099fe8)
9fa0: 00000001 ef092100 00000000 ef092100 ef098000 00000015 c0399f2c c0579d74
9fc0: 0000406a 413fc090 00000000 00000000 00000000 ef099fe8 c00666ec c000f46c
9fe0: 20000113 ffffffff
[<c0012644>] (__irq_svc+0x44/0x78) from [<c000f46c>] (arch_cpu_idle+0x34/0x3c)
[<c000f46c>] (arch_cpu_idle+0x34/0x3c) from [<c0053980>] (cpu_startup_entry+0xa8/0x10c)
[<c0053980>] (cpu_startup_entry+0xa8/0x10c) from [<000085a4>] (0x85a4)

We are in an interrupt context (IPI) and we are calling clk_get_rate in the
set_mode function which in turn ends up by getting a mutex... Even if that
does not hang, it is a potential kernel deadlock.

It is not allowed to call clk_get_rate() from interrupt context. To
avoid such calls the timer input frequency is stored in the driver's
data struct which makes it accessible to the driver in any context.

[dlezcano] completed the changelog with the WARN trace and added a more
detailed description. Tested on zync zc702.

Acked-by: Daniel Lezcano <daniel.lezcano@linaro.org>
Tested-by: Daniel Lezcano <daniel.lezcano@linaro.org>
Signed-off-by: Soren Brinkmann <soren.brinkmann@xilinx.com>
Signed-off-by: Daniel Lezcano <daniel.lezcano@linaro.org>

1 files changed, 13 insertions, 8 deletions

diff --git a/drivers/clocksource/cadence_ttc_timer.c b/drivers/clocksource/cadence_ttc_timer.c
index b2bb3a4bc205..a92350b55d32 100644
--- a/drivers/clocksource/cadence_ttc_timer.c
+++ b/drivers/clocksource/cadence_ttc_timer.c
@@ -67,11 +67,13 @@
  * struct ttc_timer - This definition defines local timer structure
  *
  * @base_addr:  Base address of timer
+ * @freq:       Timer input clock frequency
  * @clk:        Associated clock source
  * @clk_rate_change_nb  Notifier block for clock rate changes
  */
 struct ttc_timer {
         void __iomem *base_addr;
+        unsigned long freq;
         struct clk *clk;
         struct notifier_block clk_rate_change_nb;
 };
@@ -196,9 +198,8 @@ static void ttc_set_mode(enum clock_event_mode mode,
 
         switch (mode) {
         case CLOCK_EVT_MODE_PERIODIC:
-                ttc_set_interval(timer,
-                                DIV_ROUND_CLOSEST(clk_get_rate(ttce->ttc.clk),
-                                        PRESCALE * HZ));
+                ttc_set_interval(timer, DIV_ROUND_CLOSEST(ttce->ttc.freq,
+                                                PRESCALE * HZ));
                 break;
         case CLOCK_EVT_MODE_ONESHOT:
         case CLOCK_EVT_MODE_UNUSED:
@@ -273,6 +274,8 @@ static void __init ttc_setup_clocksource(struct clk *clk, void __iomem *base)
                 return;
         }
 
+        ttccs->ttc.freq = clk_get_rate(ttccs->ttc.clk);
+
         ttccs->ttc.clk_rate_change_nb.notifier_call =
                 ttc_rate_change_clocksource_cb;
         ttccs->ttc.clk_rate_change_nb.next = NULL;
@@ -298,16 +301,14 @@ static void __init ttc_setup_clocksource(struct clk *clk, void __iomem *base)
         __raw_writel(CNT_CNTRL_RESET,
                      ttccs->ttc.base_addr + TTC_CNT_CNTRL_OFFSET);
 
-        err = clocksource_register_hz(&ttccs->cs,
-                        clk_get_rate(ttccs->ttc.clk) / PRESCALE);
+        err = clocksource_register_hz(&ttccs->cs, ttccs->ttc.freq / PRESCALE);
         if (WARN_ON(err)) {
                 kfree(ttccs);
                 return;
         }
 
         ttc_sched_clock_val_reg = base + TTC_COUNT_VAL_OFFSET;
-        setup_sched_clock(ttc_sched_clock_read, 16,
-                        clk_get_rate(ttccs->ttc.clk) / PRESCALE);
+        setup_sched_clock(ttc_sched_clock_read, 16, ttccs->ttc.freq / PRESCALE);
 }
 
 static int ttc_rate_change_clockevent_cb(struct notifier_block *nb,
@@ -334,6 +335,9 @@ static int ttc_rate_change_clockevent_cb(struct notifier_block *nb,
                                 ndata->new_rate / PRESCALE);
                 local_irq_restore(flags);
 
+                /* update cached frequency */
+                ttc->freq = ndata->new_rate;
+
                 /* fall through */
         }
         case PRE_RATE_CHANGE:
@@ -367,6 +371,7 @@ static void __init ttc_setup_clockevent(struct clk *clk,
         if (clk_notifier_register(ttcce->ttc.clk,
                                 &ttcce->ttc.clk_rate_change_nb))
                 pr_warn("Unable to register clock notifier.\n");
+        ttcce->ttc.freq = clk_get_rate(ttcce->ttc.clk);
 
         ttcce->ttc.base_addr = base;
         ttcce->ce.name = "ttc_clockevent";
@@ -396,7 +401,7 @@ static void __init ttc_setup_clockevent(struct clk *clk,
         }
 
         clockevents_config_and_register(&ttcce->ce,
-                        clk_get_rate(ttcce->ttc.clk) / PRESCALE, 1, 0xfffe);
+                        ttcce->ttc.freq / PRESCALE, 1, 0xfffe);
 }
 
 /**