From 0f2c1fde7139179aa1e5f29f90faf2e5db54ba07 Mon Sep 17 00:00:00 2001 From: Daniel Lezcano Date: Mon, 17 Jun 2013 18:00:46 +0200 Subject: tick: fix tick_broadcast_pending_mask not cleared 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] [] (unwind_backtrace+0x0/0xf8) from [] (show_stack+0x10/0x14) [ 25.629616] [] (show_stack+0x10/0x14) from [] (dump_stack+0x80/0xc4) [ 25.629633] [] (dump_stack+0x80/0xc4) from [] (warn_slowpath_common+0x64/0x88) [ 25.629646] [] (warn_slowpath_common+0x64/0x88) from [] (warn_slowpath_null+0x1c/0x24) [ 25.629657] [] (warn_slowpath_null+0x1c/0x24) from [] (tick_broadcast_oneshot_control+0x1a4/0x1d0) [ 25.629670] [] (tick_broadcast_oneshot_control+0x1a4/0x1d0) from [] (tick_notify+0x240/0x40c) [ 25.629685] [] (tick_notify+0x240/0x40c) from [] (notifier_call_chain+0x44/0x84) [ 25.629699] [] (notifier_call_chain+0x44/0x84) from [] (raw_notifier_call_chain+0x18/0x20) [ 25.629712] [] (raw_notifier_call_chain+0x18/0x20) from [] (clockevents_notify+0x28/0x170) [ 25.629726] [] (clockevents_notify+0x28/0x170) from [] (cpuidle_idle_call+0x11c/0x168) [ 25.629739] [] (cpuidle_idle_call+0x11c/0x168) from [] (arch_cpu_idle+0x8/0x38) [ 25.629755] [] (arch_cpu_idle+0x8/0x38) from [] (cpu_startup_entry+0x60/0x134) [ 25.629767] [] (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 Reported-by: Joseph Lo --- 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 d067c01586f5..58d88e828d38 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 -- cgit v1.2.3