From mboxrd@z Thu Jan 1 00:00:00 1970 From: Mukesh Ojha Subject: Re: [PATCH] cpu/hotplug: Fix rollback during error-out in takedown_cpu() Date: Wed, 5 Sep 2018 17:39:37 +0530 Message-ID: References: <1536042803-6152-1-git-send-email-neeraju@codeaurora.org> Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 8bit Return-path: In-Reply-To: Content-Language: en-US Sender: linux-kernel-owner@vger.kernel.org To: Thomas Gleixner , Neeraj Upadhyay Cc: josh@joshtriplett.org, peterz@infradead.org, mingo@kernel.org, jiangshanlai@gmail.com, dzickus@redhat.com, brendan.jackman@arm.com, malat@debian.org, linux-kernel@vger.kernel.org, sramana@codeaurora.org, linux-arm-msm@vger.kernel.org List-Id: linux-arm-msm@vger.kernel.org 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 >> --- >> 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 > > > > > >