Messages in this thread Patch in this message | | | Subject | Re: [PATCH] cpu/hotplug: Fix rollback during error-out in takedown_cpu() | From | Mukesh Ojha <> | Date | Wed, 5 Sep 2018 17:39:37 +0530 |
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On 9/5/2018 5:03 PM, Thomas Gleixner wrote: > On Tue, 4 Sep 2018, Neeraj Upadhyay wrote: >> If takedown_cpu() fails during _cpu_down(), st->state is reset, >> by calling cpuhp_reset_state(). This results in an additional >> increment of st->state, which results in CPUHP_AP_SMPBOOT_THREADS >> state being skipped during rollback. Fix this by not calling >> cpuhp_reset_state() and doing the state reset directly in >> _cpu_down(). >> >> Fixes: 4dddfb5faa61 ("smp/hotplug: Rewrite AP state machine core") >> Signed-off-by: Neeraj Upadhyay <neeraju@codeaurora.org> >> --- >> kernel/cpu.c | 9 ++++++++- >> 1 file changed, 8 insertions(+), 1 deletion(-) >> >> diff --git a/kernel/cpu.c b/kernel/cpu.c >> index aa7fe85..9f49edb 100644 >> --- a/kernel/cpu.c >> +++ b/kernel/cpu.c >> @@ -970,7 +970,14 @@ static int __ref _cpu_down(unsigned int cpu, int tasks_frozen, >> */ >> ret = cpuhp_down_callbacks(cpu, st, target); >> if (ret && st->state > CPUHP_TEARDOWN_CPU && st->state < prev_state) { >> - cpuhp_reset_state(st, prev_state); >> + /* >> + * As st->last is not set, cpuhp_reset_state() increments >> + * st->state, which results in CPUHP_AP_SMPBOOT_THREADS being >> + * skipped during rollback. So, don't use it here. >> + */ >> + st->rollback = true; >> + st->target = prev_state; >> + st->bringup = !st->bringup; > No, this is just papering over the actual problem. > > The state inconsistency happens in take_cpu_down() when it returns with a > failure from __cpu_disable() because that returns with state = TEARDOWN_CPU > and st->state is then incremented in undo_cpu_down(). > > That's the real issue and we need to analyze the whole cpu_down rollback > logic first.
Could this be done like below ?
diff --git a/kernel/cpu.c b/kernel/cpu.c index aa7fe85..47bce90 100644 --- a/kernel/cpu.c +++ b/kernel/cpu.c @@ -802,17 +802,18 @@ static int take_cpu_down(void *_param) int err, cpu = smp_processor_id(); int ret;
- /* Ensure this CPU doesn't handle any more interrupts. */ - err = __cpu_disable(); - if (err < 0) - return err; - /* * We get here while we are in CPUHP_TEARDOWN_CPU state and we must not * do this step again. */ WARN_ON(st->state != CPUHP_TEARDOWN_CPU); st->state--; + + /* Ensure this CPU doesn't handle any more interrupts. */ + err = __cpu_disable(); + if (err < 0) + return err; + /* Invoke the former CPU_DYING callbacks */
Thanks, Mukesh > > > > > >
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