Messages in this thread Patch in this message | | | From | Sudeep Holla <> | Subject | [PATCH] cpufreq: flush any pending policy update work scheduled before freeing | Date | Thu, 17 Oct 2019 17:35:03 +0100 |
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dev_pm_qos_remove_request ends calling {max,min}_freq_req QoS notifiers which schedule policy update work. It may end up racing with the freeing the policy and unregistering the driver.
One possible race is as below where the cpufreq_driver is unregistered but the scheduled work gets executed at later stage when cpufreq_driver is NULL(i.e. after freeing the policy and driver)
Unable to handle kernel NULL pointer dereference at virtual address 0000001c pgd = (ptrval) [0000001c] *pgd=80000080204003, *pmd=00000000 Internal error: Oops: 206 [#1] SMP THUMB2 Modules linked in: CPU: 0 PID: 34 Comm: kworker/0:1 Not tainted 5.4.0-rc3-00006-g67f5a8081a4b #86 Hardware name: ARM-Versatile Express Workqueue: events handle_update PC is at cpufreq_set_policy+0x58/0x228 LR is at dev_pm_qos_read_value+0x77/0xac Control: 70c5387d Table: 80203000 DAC: fffffffd Process kworker/0:1 (pid: 34, stack limit = 0x(ptrval)) (cpufreq_set_policy) from (refresh_frequency_limits.part.24+0x37/0x48) (refresh_frequency_limits.part.24) from (handle_update+0x2f/0x38) (handle_update) from (process_one_work+0x16d/0x3cc) (process_one_work) from (worker_thread+0xff/0x414) (worker_thread) from (kthread+0xff/0x100) (kthread) from (ret_from_fork+0x11/0x28)
Cc: "Rafael J. Wysocki" <rjw@rjwysocki.net> Cc: Viresh Kumar <viresh.kumar@linaro.org> Signed-off-by: Sudeep Holla <sudeep.holla@arm.com> --- drivers/cpufreq/cpufreq.c | 3 +++ 1 file changed, 3 insertions(+)
Hi Rafael, Viresh,
This fixed the boot issue I reported[1] on TC2 with bL switcher enabled. I have based this patch on -rc3 and not on top of your patches. This only fixes the boot issue but I hit the other crashes while continuously switching on and off the bL switcher that register/unregister the driver Your patch series fixes them. I can based this on top of those if you prefer.
Regards, Sudeep
[1] https://lore.kernel.org/linux-pm/20191015155735.GA29105@bogus/
diff --git a/drivers/cpufreq/cpufreq.c b/drivers/cpufreq/cpufreq.c index c52d6fa32aac..b703c29a84be 100644 --- a/drivers/cpufreq/cpufreq.c +++ b/drivers/cpufreq/cpufreq.c @@ -1278,6 +1278,9 @@ static void cpufreq_policy_free(struct cpufreq_policy *policy) } dev_pm_qos_remove_request(policy->min_freq_req); + /* flush the pending policy->update work before freeing the policy */ + if (work_pending(&policy->update)) + flush_work(&policy->update); kfree(policy->min_freq_req); cpufreq_policy_put_kobj(policy); -- 2.17.1
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