From d4c7c28806616809e3baa0b7cd8c665516b2726d Mon Sep 17 00:00:00 2001 From: =?UTF-8?q?Niklas=20S=C3=B6derlund?= Date: Thu, 11 Feb 2021 14:43:18 +0100 Subject: [PATCH] timekeeping: Allow runtime PM from change_clocksource() MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit The struct clocksource callbacks enable() and disable() are described as a way to allow clock sources to enter a power save mode. See commit 4614e6adafa2 ("clocksource: add enable() and disable() callbacks") But using runtime PM from these callbacks triggers a cyclic lockdep warning when switching clock source using change_clocksource(). # echo e60f0000.timer > /sys/devices/system/clocksource/clocksource0/current_clocksource ====================================================== WARNING: possible circular locking dependency detected ------------------------------------------------------ migration/0/11 is trying to acquire lock: ffff0000403ed220 (&dev->power.lock){-...}-{2:2}, at: __pm_runtime_resume+0x40/0x74 but task is already holding lock: ffff8000113c8f88 (tk_core.seq.seqcount){----}-{0:0}, at: multi_cpu_stop+0xa4/0x190 which lock already depends on the new lock. the existing dependency chain (in reverse order) is: -> #2 (tk_core.seq.seqcount){----}-{0:0}: ktime_get+0x28/0xa0 hrtimer_start_range_ns+0x210/0x2dc generic_sched_clock_init+0x70/0x88 sched_clock_init+0x40/0x64 start_kernel+0x494/0x524 -> #1 (hrtimer_bases.lock){-.-.}-{2:2}: hrtimer_start_range_ns+0x68/0x2dc rpm_suspend+0x308/0x5dc rpm_idle+0xc4/0x2a4 pm_runtime_work+0x98/0xc0 process_one_work+0x294/0x6f0 worker_thread+0x70/0x45c kthread+0x154/0x160 ret_from_fork+0x10/0x20 -> #0 (&dev->power.lock){-...}-{2:2}: _raw_spin_lock_irqsave+0x7c/0xc4 __pm_runtime_resume+0x40/0x74 sh_cmt_start+0x1c4/0x260 sh_cmt_clocksource_enable+0x28/0x50 change_clocksource+0x9c/0x160 multi_cpu_stop+0xa4/0x190 cpu_stopper_thread+0x90/0x154 smpboot_thread_fn+0x244/0x270 kthread+0x154/0x160 ret_from_fork+0x10/0x20 other info that might help us debug this: Chain exists of: &dev->power.lock --> hrtimer_bases.lock --> tk_core.seq.seqcount Possible unsafe locking scenario: CPU0 CPU1 ---- ---- lock(tk_core.seq.seqcount); lock(hrtimer_bases.lock); lock(tk_core.seq.seqcount); lock(&dev->power.lock); *** DEADLOCK *** 2 locks held by migration/0/11: #0: ffff8000113c9278 (timekeeper_lock){-.-.}-{2:2}, at: change_clocksource+0x2c/0x160 #1: ffff8000113c8f88 (tk_core.seq.seqcount){----}-{0:0}, at: multi_cpu_stop+0xa4/0x190 Rework change_clocksource() so it enables the new clocksource and disables the old clocksource outside of the timekeeper_lock and seqcount write held region. There is no requirement that these callbacks are invoked from the lock held region. Signed-off-by: Niklas Söderlund Signed-off-by: Thomas Gleixner Tested-by: Wolfram Sang Link: https://lore.kernel.org/r/20210211134318.323910-1-niklas.soderlund+renesas@ragnatech.se --- kernel/time/timekeeping.c | 36 +++++++++++++++++++++++------------- 1 file changed, 23 insertions(+), 13 deletions(-) diff --git a/kernel/time/timekeeping.c b/kernel/time/timekeeping.c index 77bafd8c8df2..81fe2a33b80c 100644 --- a/kernel/time/timekeeping.c +++ b/kernel/time/timekeeping.c @@ -1427,35 +1427,45 @@ static void __timekeeping_set_tai_offset(struct timekeeper *tk, s32 tai_offset) static int change_clocksource(void *data) { struct timekeeper *tk = &tk_core.timekeeper; - struct clocksource *new, *old; + struct clocksource *new, *old = NULL; unsigned long flags; + bool change = false; new = (struct clocksource *) data; - raw_spin_lock_irqsave(&timekeeper_lock, flags); - write_seqcount_begin(&tk_core.seq); - - timekeeping_forward_now(tk); /* * If the cs is in module, get a module reference. Succeeds * for built-in code (owner == NULL) as well. */ if (try_module_get(new->owner)) { - if (!new->enable || new->enable(new) == 0) { - old = tk->tkr_mono.clock; - tk_setup_internals(tk, new); - if (old->disable) - old->disable(old); - module_put(old->owner); - } else { + if (!new->enable || new->enable(new) == 0) + change = true; + else module_put(new->owner); - } } + + raw_spin_lock_irqsave(&timekeeper_lock, flags); + write_seqcount_begin(&tk_core.seq); + + timekeeping_forward_now(tk); + + if (change) { + old = tk->tkr_mono.clock; + tk_setup_internals(tk, new); + } + timekeeping_update(tk, TK_CLEAR_NTP | TK_MIRROR | TK_CLOCK_WAS_SET); write_seqcount_end(&tk_core.seq); raw_spin_unlock_irqrestore(&timekeeper_lock, flags); + if (old) { + if (old->disable) + old->disable(old); + + module_put(old->owner); + } + return 0; }