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Message-ID: <1538311.12EC6AbbfU@vostro.rjw.lan> Date: Mon, 06 Jan 2014 02:07:19 +0100 From: "Rafael J. Wysocki" <rjw@...ysocki.net> To: Dmitry Torokhov <dmitry.torokhov@...il.com> Cc: Viresh Kumar <viresh.kumar@...aro.org>, Jane Li <jiel@...vell.com>, "cpufreq@...r.kernel.org" <cpufreq@...r.kernel.org>, "linux-pm@...r.kernel.org" <linux-pm@...r.kernel.org>, Linux Kernel Mailing List <linux-kernel@...r.kernel.org> Subject: Re: [PATCH v4] cpufreq: Fix timer/workqueue corruption by protecting reading governor_enabled On Friday, January 03, 2014 03:10:23 PM Dmitry Torokhov wrote: > On Fri, Jan 03, 2014 at 03:40:16PM +0530, Viresh Kumar wrote: > > On 3 January 2014 14:47, <jiel@...vell.com> wrote: > > > From: Jane Li <jiel@...vell.com> > > > > > > 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@...vell.com> > > > --- > > > 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@...aro.org> > > Reviewed-by: Dmitry Torokhov <dmitry.torokhov@...il.com> Queued up for 3.14, thanks! -- I speak only for myself. Rafael J. Wysocki, Intel Open Source Technology Center. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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