From mboxrd@z Thu Jan 1 00:00:00 1970 From: rjw@rjwysocki.net (Rafael J. Wysocki) Date: Sat, 20 Aug 2016 03:29:27 +0200 Subject: Kernel warning in cpufreq_add_dev() In-Reply-To: <20160819110032.GM1041@n2100.armlinux.org.uk> References: <20160819110032.GM1041@n2100.armlinux.org.uk> Message-ID: <1601399.OxUAWWKTJN@vostro.rjw.lan> To: linux-arm-kernel@lists.infradead.org List-Id: linux-arm-kernel.lists.infradead.org On Friday, August 19, 2016 12:00:32 PM Russell King - ARM Linux wrote: > While checking the kernel on SA1110 Assabet, CPUFREQ issues a warning: > > ------------[ cut here ]------------ > WARNING: CPU: 0 PID: 1 at /home/rmk/git/linux-rmk/drivers/cpufreq/cpufreq.c:1080 cpufreq_add_dev+0x140/0x62c > Modules linked in: > CPU: 0 PID: 1 Comm: swapper Not tainted 4.8.0-rc2+ #883 > Hardware name: Intel-Assabet > Backtrace: > [] (dump_backtrace) from [] (show_stack+0x18/0x1c) > r6:00000000 r5:c05e87c3 r4:00000000 > [] (show_stack) from [] (dump_stack+0x20/0x28) > [] (dump_stack) from [] (__warn+0xd0/0xfc) > [] (__warn) from [] (warn_slowpath_null+0x28/0x30) > r10:00000000 r8:00000000 r7:00000000 r6:c064525c r5:00000000 r4:00000000 > [] (warn_slowpath_null) from [] (cpufreq_add_dev+0x140/0x62c) > [] (cpufreq_add_dev) from [] (bus_probe_device+0x5c/0x84) > r10:00000000 r8:00000000 r7:00000000 r6:c064525c r5:c0657d60 r4:c065a9f8 > [] (bus_probe_device) from [] (device_add+0x390/0x520) > r6:c0645264 r5:00000000 r4:c064525c > [] (device_add) from [] (device_register+0x1c/0x20) > r10:c0639848 r8:c061e524 r7:00000001 r6:00000000 r5:c064525c r4:c064525c > [] (device_register) from [] (register_cpu+0x88/0xac) > r4:c0645254 > [] (register_cpu) from [] (topology_init+0x20/0x2c) > r7:c0660b20 r6:c063f4a0 r5:c0639834 r4:00000000 > [] (topology_init) from [] (do_one_initcall+0xc0/0x178) > r4:00000004 > [] (do_one_initcall) from [] (kernel_init_freeable+0xfc/0x1c4) > r10:c0639848 r9:00000000 r8:00000088 r7:c0660b20 r6:c063f4a0 r5:c0639834 > r4:00000004 > [] (kernel_init_freeable) from [] (kernel_init+0x10/0xf4) > r10:00000000 r8:00000000 r7:00000000 r6:00000000 r5:c050d720 r4:00000000 > [] (kernel_init) from [] (ret_from_fork+0x14/0x24) > r4:00000000 > ---[ end trace df94656649275917 ]--- > > This is because of an incompatibility between the expectations of cpufreq > and how register_cpu() works: > > int register_cpu(struct cpu *cpu, int num) > { > ... > error = device_register(&cpu->dev); > if (!error) > per_cpu(cpu_sys_devices, num) = &cpu->dev; > > When the device is registered via device_register(), any subsystems > registered for the cpu_subsys will have their "add_dev" method called. > > The cpufreq add_dev, via cpufreq_online() and cpufreq_policy_alloc(), > tries to get the CPU device: > > static struct cpufreq_policy *cpufreq_policy_alloc(unsigned int cpu) > { > struct device *dev = get_cpu_device(cpu); > if (WARN_ON(!dev)) > return NULL; > > but this fails: > > struct device *get_cpu_device(unsigned cpu) > { > if (cpu < nr_cpu_ids && cpu_possible(cpu)) > return per_cpu(cpu_sys_devices, cpu); > > because the percpu data has not yet been written - it'll be written > after a successful device registration. So, using get_cpu_device() > from within cpufreq_add_dev() is broken, and results in the above > kernel warning. Ironically enough, cpufreq_policy_alloc() doesn't even use the value of dev for anything other than the check, so we can simply get rid of it (as per the appended patch). add_cpu_dev_symlink() will still be problematic, though, if I'm not mistaken. I wonder how that works on other platforms. --- drivers/cpufreq/cpufreq.c | 4 ---- 1 file changed, 4 deletions(-) Index: linux-pm/drivers/cpufreq/cpufreq.c =================================================================== --- linux-pm.orig/drivers/cpufreq/cpufreq.c +++ linux-pm/drivers/cpufreq/cpufreq.c @@ -1073,13 +1073,9 @@ static void handle_update(struct work_st static struct cpufreq_policy *cpufreq_policy_alloc(unsigned int cpu) { - struct device *dev = get_cpu_device(cpu); struct cpufreq_policy *policy; int ret; - if (WARN_ON(!dev)) - return NULL; - policy = kzalloc(sizeof(*policy), GFP_KERNEL); if (!policy) return NULL;