On Tue, 2013-06-18 at 00:15 +0800, Daniel Lezcano wrote: > 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@xxxxxxxxxx> > Reported-by: Joseph Lo <josephl@xxxxxxxxxx> > --- Daniel, Thanks, This patch fixes the problem indeed. I can't reproduce it anymore. Verified on Tegra30 and Tegra114 platform. Looks good to me. Tested-by: Joseph Lo <josephl@xxxxxxxxxx> Joseph -- To unsubscribe from this list: send the line "unsubscribe linux-tegra" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
