Subject: cpufreq: powernow-k8: Remove bogus smp_processor_id() usage From: Thomas Gleixner Date: Sat, 27 Oct 2012 12:26:44 +0200 commit 6889125b (cpufreq/powernow-k8: workqueue user shouldn't migrate the kworker to another CPU) has a broken optimization of calling powernowk8_target_fn() directly from powernowk8_target() which results in the following splat: [ 11.789468] BUG: using smp_processor_id() in preemptible [00000000] code: modprobe/505 [ 11.809594] caller is powernowk8_target+0x20/0x48 [powernow_k8] [ 12.001748] Pid: 505, comm: modprobe Not tainted 3.6.3 #3 [ 12.016836] Call Trace: [ 12.025971] [] debug_smp_processor_id+0xcc/0xe8 [ 12.042518] [] powernowk8_target+0x20/0x48 [powernow_k8] [ 12.060733] [] __cpufreq_driver_target+0x82/0x8a [ 12.077550] [] cpufreq_governor_userspace+0x265/0x2c0 [ 12.120378] [] ? __blocking_notifier_call_chain+0x56/0x60 [ 12.138862] [] __cpufreq_governor+0x8c/0xc9 [ 12.155193] [] __cpufreq_set_policy+0x212/0x21e [ 12.172148] [] cpufreq_add_dev_interface+0x2a2/0x2bc [ 12.189855] [] ? cpufreq_update_policy+0x124/0x124 [ 12.207096] [] cpufreq_add_dev+0x4a4/0x4b4 [ 12.223161] [] subsys_interface_register+0x95/0xc5 [ 12.240386] [] ? _raw_spin_lock_irqsave+0x24/0x46 [ 12.257477] [] cpufreq_register_driver+0xd2/0x1bf [ 12.274545] [] powernowk8_init+0x193/0x1dc [powernow_k8] [ 12.292794] [] ? powernowk8_cpu_init+0xc53/0xc53 [powernow_k8] [ 12.312004] [] do_one_initcall+0x7f/0x136 [ 12.327594] [] sys_init_module+0x17b0/0x197e [ 12.343718] [] ? ddebug_proc_write+0xde/0xde [ 12.359767] [] system_call_fastpath+0x16/0x1b This is fully preemptible non cpu bound context though the comment in the code says: * Must run on @pol->cpu. cpufreq core is responsible for ensuring * that we're bound to the current CPU and pol->cpu stays online. The core only guarantees that pol->cpu stays online, but it has no way to bind the thread and this needs to be fully preemptible context as powernowk8_target_fn() calls functions which might sleep. So the correct solution is to always go through work_on_cpu(). Reported-and-tested-by: Carsten Emde Cc: Tejun Heo Cc: Rafael J. Wysocki Cc: Andreas Herrmann Cc: stable@vger.kernel.org Signed-off-by: Thomas Gleixner --- drivers/cpufreq/powernow-k8.c | 11 +++++------ 1 file changed, 5 insertions(+), 6 deletions(-) Index: linux-stable/drivers/cpufreq/powernow-k8.c =================================================================== --- linux-stable.orig/drivers/cpufreq/powernow-k8.c +++ linux-stable/drivers/cpufreq/powernow-k8.c @@ -1224,13 +1224,12 @@ static int powernowk8_target(struct cpuf .relation = relation }; /* - * Must run on @pol->cpu. cpufreq core is responsible for ensuring - * that we're bound to the current CPU and pol->cpu stays online. + * Must run on @pol->cpu. We queue it on the target cpu even + * if we are currently on the target cpu. This is preemptible + * non cpu bound context, so we can't call the target function + * directly. */ - if (smp_processor_id() == pol->cpu) - return powernowk8_target_fn(&pta); - else - return work_on_cpu(pol->cpu, powernowk8_target_fn, &pta); + return work_on_cpu(pol->cpu, powernowk8_target_fn, &pta); } /* Driver entry point to verify the policy and range of frequencies */