linux-kernel - SMP boot issue during system resume

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Message-ID: <dfa19ca7-c4c6-4386-a54d-44d623c8d3ed@quicinc.com>
Date: Mon, 22 Dec 2025 11:30:19 +0530
From: Pavan Kondeti <pavan.kondeti@....qualcomm.com>
To: Will Deacon <will@...nel.org>, Mark Rutland <mark.rutland@....com>,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        linux-arm-msm@...r.kernel.org
Subject: SMP boot issue during system resume

Hi

We are seeing a SMP boot issue during system resume when CPUs are brought 
online via pm_sleep_enable_secondary_cpus()->thaw_secondary_cpus()->_cpu_up() 
on ARM64.

The _cpu_up() sets a global variable

secondary_data.task = idle;

and wait for the secondary CPU to come online. A 5 second timeout is
used here. If at all, the secondary CPU comes online after this timeout,
we expect it to loop in kernel via __secondary_too_slow(). However, this
depends on secondary_data.task value. Since we are bringing all disabled
cores, after timeout, we set this global variable to the next CPU idle
task and the late secondary CPU thinks the value is its idle task and
does not enter __secondary_too_slow().

An earlier attempt [1] to fix similar issue incrased the timout to 5
seconds. We could reproduce this issue in Linux guest where vCPU
scheduling latency can be higher under heavy load on the host.

I would like to seek your inputs on how we can improve the current
situation. We would like to avoid __secondary_too_slow() spin even when
the CPU comes late. This is probably not a desired behavior for other cases like 
Linux running bare metal or some guests. Having a Kconfig option or
kernel param might help here.

[1] https://lore.kernel.org/all/20190827151815.2160-1-will@kernel.org/