On 3/14/2024 6:14 PM, Frederic Weisbecker wrote:
On Thu, Mar 14, 2024 at 03:05:53PM -0700, Boqun Feng wrote:I notice CPU3 didn't have its own non-deferrable timer queued (local or global), so could the following happen? timer_base_try_to_set_idle(): __get_next_timer_interrupt(): fetch_next_timer_interrupt(): // nextevt_local == nextevt_global == basej + NEXT_TIMER_MAX_DELTA // tevt->local == tevt->gloabl = KTIME_MAX timer_use_tmigr(): tmigr_cpu_deactivate(): __tmigr_cpu_deactivate(): // tmc->cpuevt.ignore untouched still == true walk_groups(&tmigr_inactive_up, ...): tmigr_inactive_up(): data->remote = true; tmigr_update_events(): if (child) { // child is NULL ... } else { first_childevt = evt = data->evt; if (evt->ignore && !remote) return true; // no remote tick is picked. ... }Nice catch! Florian can you try the following? From b0e335371ed758f68bf4f501246298c98a615b04 Mon Sep 17 00:00:00 2001 From: Frederic Weisbecker <frederic@xxxxxxxxxx> Date: Fri, 15 Mar 2024 00:21:01 +0100 Subject: [PATCH] timer/migration: Remove buggy early return on deactivation When a CPU enters into idle and deactivates itself from the timer migration hierarchy without any global timer of its own to propagate, the group event of that CPU is set to "ignore" and tmigr_update_events() accordingly performs an early return without considering timers queued by other CPUs. If the hierarchy has a single level, and the CPU is the last one to enter idle, it will ignore others' global timers, as in the following layout: [GRP0:0] migrator = 0 active = 0 nextevt = T0i / \ 0 1 active (T0i) idle (T1) 0) CPU 0 is active thus its event is ignored (the letter 'i') and so are upper levels' events. CPU 1 is idle and has the timer T1 enqueued. [GRP0:0] migrator = NONE active = NONE nextevt = T0i / \ 0 1 idle (T0i) idle (T1) 1) CPU 0 goes idle without global event queued. Therefore KTIME_MAX is pushed as its next expiry and its own event kept as "ignore". As a result tmigr_update_events() ignores T1 and CPU 0 goes to idle with T1 unhandled. This isn't proper to single level hierarchy though. A similar issue, although slightly different, may arise on multi-level: [GRP1:0] migrator = GRP0:0 active = GRP0:0 nextevt = T0:0i, T0:1 / \ [GRP0:0] [GRP0:1] migrator = 0 migrator = NONE active = 0 active = NONE nextevt = T0i nextevt = T2 / \ / \ 0 (T0i) 1 (T1) 2 (T2) 3 idle idle idle idle 0) CPU 0 is active thus its event is ignored (the letter 'i') and so are upper levels' events. CPU 1 is idle and has the timer T1 enqueued. CPU 2 also has a timer. The expiry order is T0 (ignored) < T1 < T2 [GRP1:0] migrator = GRP0:0 active = GRP0:0 nextevt = T0:0i, T0:1 / \ [GRP0:0] [GRP0:1] migrator = NONE migrator = NONE active = NONE active = NONE nextevt = T0i nextevt = T2 / \ / \ 0 (T0i) 1 (T1) 2 (T2) 3 idle idle idle idle 1) CPU 0 goes idle without global event queued. Therefore KTIME_MAX is pushed as its next expiry and its own event kept as "ignore". As a result tmigr_update_events() ignores T1. The change only propagated up to 1st level so far. [GRP1:0] migrator = NONE active = NONE nextevt = T0:1 / \ [GRP0:0] [GRP0:1] migrator = NONE migrator = NONE active = NONE active = NONE nextevt = T0i nextevt = T2 / \ / \ 0 (T0i) 1 (T1) 2 (T2) 3 idle idle idle idle 2) The change now propagates up to the top. tmigr_update_events() finds that the child event is ignored and thus removes it. The top level next event is now T2 which is returned to CPU 0 as its next effective expiry to take account for as the global idle migrator. However T1 has been ignored along the way, leaving it unhandled. Fix those issues with removing the buggy related early return. Ignored child events must not prevent from evaluating the other events within the same group. Reported-by: Boqun Feng <boqun.feng@xxxxxxxxx> Reported-by: Florian Fainelli <f.fainelli@xxxxxxxxx>
Gave it a good 20 cold boots and suspend to DRAM cycles and none of those triggered the reported behavior:
Reported-by: Florian Fainelli <florian.fainelli@xxxxxxxxxxxx> Tested-by: Florian Fainelli <florian.fainelli@xxxxxxxxxxxx> Thanks for the quick fix Frederic! -- Florian
