On 3 January 2014 14:47, <jiel@xxxxxxxxxxx> wrote: > From: Jane Li <jiel@xxxxxxxxxxx> > > When a CPU is hot removed we'll cancel all the delayed work items via > gov_cancel_work(). Sometimes the delayed work function determines that > it should adjust the delay for all other CPUs that the policy is > managing. If this scenario occurs, the canceling CPU will cancel its own > work but queue up the other CPUs works to run. > > Commit 3617f2(cpufreq: Fix timer/workqueue corruption due to double > queueing) has tried to fix this, but reading governor_enabled is not > protected by cpufreq_governor_lock. Even though od_dbs_timer() checks > governor_enabled before gov_queue_work(), this scenario may occur. For > example: > > CPU0 CPU1 > ---- ---- > cpu_down() > ... <work runs> > __cpufreq_remove_dev() od_dbs_timer() > __cpufreq_governor() policy->governor_enabled > policy->governor_enabled = false; > cpufreq_governor_dbs() > case CPUFREQ_GOV_STOP: > gov_cancel_work(dbs_data, policy); > cpu0 work is canceled > timer is canceled > cpu1 work is canceled > <waits for cpu1> > gov_queue_work(*, *, true); > cpu0 work queued > cpu1 work queued > cpu2 work queued > ... > cpu1 work is canceled > cpu2 work is canceled > ... > > At the end of the GOV_STOP case cpu0 still has a work queued to > run although the code is expecting all of the works to be > canceled. __cpufreq_remove_dev() will then proceed to > re-initialize all the other CPUs works except for the CPU that is > going down. The CPUFREQ_GOV_START case in cpufreq_governor_dbs() > will trample over the queued work and debugobjects will spit out > a warning: > > WARNING: at lib/debugobjects.c:260 debug_print_object+0x94/0xbc() > ODEBUG: init active (active state 0) object type: timer_list hint: delayed_work_timer_fn+0x0/0x14 > Modules linked in: > CPU: 1 PID: 1205 Comm: sh Tainted: G W 3.10.0 #200 > [<c01144f0>] (unwind_backtrace+0x0/0xf8) from [<c0111d98>] (show_stack+0x10/0x14) > [<c0111d98>] (show_stack+0x10/0x14) from [<c01272cc>] (warn_slowpath_common+0x4c/0x68) > [<c01272cc>] (warn_slowpath_common+0x4c/0x68) from [<c012737c>] (warn_slowpath_fmt+0x30/0x40) > [<c012737c>] (warn_slowpath_fmt+0x30/0x40) from [<c034c640>] (debug_print_object+0x94/0xbc) > [<c034c640>] (debug_print_object+0x94/0xbc) from [<c034c7f8>] (__debug_object_init+0xc8/0x3c0) > [<c034c7f8>] (__debug_object_init+0xc8/0x3c0) from [<c01360e0>] (init_timer_key+0x20/0x104) > [<c01360e0>] (init_timer_key+0x20/0x104) from [<c04872ac>] (cpufreq_governor_dbs+0x1dc/0x68c) > [<c04872ac>] (cpufreq_governor_dbs+0x1dc/0x68c) from [<c04833a8>] (__cpufreq_governor+0x80/0x1b0) > [<c04833a8>] (__cpufreq_governor+0x80/0x1b0) from [<c0483704>] (__cpufreq_remove_dev.isra.12+0x22c/0x380) > [<c0483704>] (__cpufreq_remove_dev.isra.12+0x22c/0x380) from [<c0692f38>] (cpufreq_cpu_callback+0x48/0x5c) > [<c0692f38>] (cpufreq_cpu_callback+0x48/0x5c) from [<c014fb40>] (notifier_call_chain+0x44/0x84) > [<c014fb40>] (notifier_call_chain+0x44/0x84) from [<c012ae44>] (__cpu_notify+0x2c/0x48) > [<c012ae44>] (__cpu_notify+0x2c/0x48) from [<c068dd40>] (_cpu_down+0x80/0x258) > [<c068dd40>] (_cpu_down+0x80/0x258) from [<c068df40>] (cpu_down+0x28/0x3c) > [<c068df40>] (cpu_down+0x28/0x3c) from [<c068e4c0>] (store_online+0x30/0x74) > [<c068e4c0>] (store_online+0x30/0x74) from [<c03a7308>] (dev_attr_store+0x18/0x24) > [<c03a7308>] (dev_attr_store+0x18/0x24) from [<c0256fe0>] (sysfs_write_file+0x100/0x180) > [<c0256fe0>] (sysfs_write_file+0x100/0x180) from [<c01fec9c>] (vfs_write+0xbc/0x184) > [<c01fec9c>] (vfs_write+0xbc/0x184) from [<c01ff034>] (SyS_write+0x40/0x68) > [<c01ff034>] (SyS_write+0x40/0x68) from [<c010e200>] (ret_fast_syscall+0x0/0x48) > > In gov_queue_work(), lock cpufreq_governor_lock before gov_queue_work, > and unlock it after __gov_queue_work(). In this way, governor_enabled > is guaranteed not changed in gov_queue_work(). > > Signed-off-by: Jane Li <jiel@xxxxxxxxxxx> > --- > drivers/cpufreq/cpufreq.c | 2 +- > drivers/cpufreq/cpufreq_governor.c | 6 +++++- > drivers/cpufreq/cpufreq_governor.h | 2 ++ > 3 files changed, 8 insertions(+), 2 deletions(-) Acked-by: Viresh Kumar <viresh.kumar@xxxxxxxxxx> -- To unsubscribe from this list: send the line "unsubscribe cpufreq" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
