The recent modification in the cpuidle framework consolidated the timer broadcast code across the different drivers by setting a new flag in the idle state. It tells the cpuidle core code to enter/exit to the broadcast mode for the cpu when entering a deep idle state. The broadcast timer enter/exit is no longer handled by the back-end driver.
This change made the local interrupt to be enabled *before* calling CLOCK_EVENT_NOTIFY_EXIT. bad or not (see below) ?
On a tegra114, a four cores system, when the flag has been introduced in the driver, the following warning appeared:
[ 25.629559] WARNING: CPU: 2 PID: 0 at kernel/time/tick-broadcast.c:578 tick_broadcast_oneshot_control +0x1a4/0x1d0() [ 25.629565] Modules linked in: [ 25.629574] CPU: 2 PID: 0 Comm: swapper/2 Not tainted 3.10.0-rc3-next-20130529+ #15 [ 25.629601] [<c00148f4>] (unwind_backtrace+0x0/0xf8) from [<c0011040>] (show_stack+0x10/0x14) [ 25.629616] [<c0011040>] (show_stack+0x10/0x14) from [<c0504248>] (dump_stack+0x80/0xc4) [ 25.629633] [<c0504248>] (dump_stack+0x80/0xc4) from [<c00231ac>] (warn_slowpath_common+0x64/0x88) [ 25.629646] [<c00231ac>] (warn_slowpath_common+0x64/0x88) from [<c00231ec>] (warn_slowpath_null+0x1c/0x24) [ 25.629657] [<c00231ec>] (warn_slowpath_null+0x1c/0x24) from [<c00667f8>] (tick_broadcast_oneshot_control+0x1a4/0x1d0) [ 25.629670] [<c00667f8>] (tick_broadcast_oneshot_control+0x1a4/0x1d0) from [<c0065cd0>] (tick_notify+0x240/0x40c) [ 25.629685] [<c0065cd0>] (tick_notify+0x240/0x40c) from [<c0044724>] (notifier_call_chain+0x44/0x84) [ 25.629699] [<c0044724>] (notifier_call_chain+0x44/0x84) from [<c0044828>] (raw_notifier_call_chain+0x18/0x20) [ 25.629712] [<c0044828>] (raw_notifier_call_chain+0x18/0x20) from [<c00650cc>] (clockevents_notify+0x28/0x170) [ 25.629726] [<c00650cc>] (clockevents_notify+0x28/0x170) from [<c033f1f0>] (cpuidle_idle_call+0x11c/0x168) [ 25.629739] [<c033f1f0>] (cpuidle_idle_call+0x11c/0x168) from [<c000ea94>] (arch_cpu_idle+0x8/0x38) [ 25.629755] [<c000ea94>] (arch_cpu_idle+0x8/0x38) from [<c005ea80>] (cpu_startup_entry+0x60/0x134) [ 25.629767] [<c005ea80>] (cpu_startup_entry+0x60/0x134) from [<804fe9a4>] (0x804fe9a4) [ 25.629772] ---[ end trace 5484e77e2531bccc ]---
I don't have the hardware, so I wasn't able to reproduce the warning but after looking a while in the code, I deduced the following:
1. the CPU2 enters a deep idle state and sets the broadcast timer 2. the timer expires, the tick_handle_oneshot_broadcast function is called, setting the tick_broadcast_pending_mask and waking up the idle cpu CPU2 3. the CPU2 exits idle and invokes tick_broadcast_oneshot_control with CLOCK_EVENT_NOTIFY_EXIT with the following code: [...] if (dev->next_event.tv64 == KTIME_MAX) goto out;
if (cpumask_test_and_clear_cpu(cpu, tick_broadcast_pending_mask)) goto out; [...]
4. if there is no next event planned for CPU2, we fulfil the first condition and we jump to the 'out' section without clearing the tick_broadcast_pending_mask
5. CPU2 goes to deep idle again and calls tick_broadcast_oneshot_control with CLOCK_NOTIFY_EVENT_ENTER but with the tick_broadcast_pending_mask set for CPU2, leading to the WARNING.
Above, it is mentionned the change moved the CLOCK_EVENT_NOTIFY_EXIT after the local interrupt were enabled. If it is before, this warning does not occur. My hypothesis is the code path described before does not happen because when a broadcast timer expires, dev->next_event.tv64 is always different from KTIME_MAX because the timer handler did not set the value yet (local interrupt are still disabled).
I don't see anywhere in the code, a clockevents_notify(ENTER/EXIT) block must be done with the local interrupt disabled in between, furthermore the function uses 'raw_spin_lock_irqsave' which make me think, we don't care about that.
Invert the conditions and make the tick broadcast code immune from the local interrupts context.
Signed-off-by: Daniel Lezcano daniel.lezcano@linaro.org Reported-by: Joseph Lo josephl@nvidia.com --- kernel/time/tick-broadcast.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-)
diff --git a/kernel/time/tick-broadcast.c b/kernel/time/tick-broadcast.c index d067c01..58d88e8 100644 --- a/kernel/time/tick-broadcast.c +++ b/kernel/time/tick-broadcast.c @@ -610,8 +610,6 @@ void tick_broadcast_oneshot_control(unsigned long reason) } else { if (cpumask_test_and_clear_cpu(cpu, tick_broadcast_oneshot_mask)) { clockevents_set_mode(dev, CLOCK_EVT_MODE_ONESHOT); - if (dev->next_event.tv64 == KTIME_MAX) - goto out; /* * The cpu which was handling the broadcast * timer marked this cpu in the broadcast @@ -625,6 +623,8 @@ void tick_broadcast_oneshot_control(unsigned long reason) tick_broadcast_pending_mask)) goto out;
+ if (dev->next_event.tv64 == KTIME_MAX) + goto out; /* * If the pending bit is not set, then we are * either the CPU handling the broadcast