Re: [PATCH] PM / OPP: cpufreq: Avoid sleeping while atomic

[Viresh Kumar]

On 17 July 2014 05:05, Stephen Boyd <sboyd@xxxxxxxxxxxxxx> wrote:
> We allocate the cpufreq table after calling rcu_read_lock(),
> which disables preemption. This causes scheduling while atomic
> warnings. Use GFP_ATOMIC instead of GFP_KERNEL and update for
> kcalloc while we're here.

I am surprised to see that this isn't reported by anybody since the time
it came into existence? Some special config option required to observe
this?

> BUG: sleeping function called from invalid context at mm/slub.c:1246
> in_atomic(): 0, irqs_disabled(): 0, pid: 80, name: modprobe
> 5 locks held by modprobe/80:
>  #0:  (&dev->mutex){......}, at: [<c050d484>] __driver_attach+0x48/0x98
>  #1:  (&dev->mutex){......}, at: [<c050d494>] __driver_attach+0x58/0x98
>  #2:  (subsys mutex#5){+.+.+.}, at: [<c050c114>] subsys_interface_register+0x38/0xc8
>  #3:  (cpufreq_rwsem){.+.+.+}, at: [<c05a9c8c>] __cpufreq_add_dev.isra.22+0x84/0x92c
>  #4:  (rcu_read_lock){......}, at: [<c05ab24c>] dev_pm_opp_init_cpufreq_table+0x18/0x10c
> Preemption disabled at:[<  (null)>]   (null)
>
> CPU: 2 PID: 80 Comm: modprobe Not tainted 3.16.0-rc3-next-20140701-00035-g286857f216aa-dirty #217
> [<c0214da8>] (unwind_backtrace) from [<c02123f8>] (show_stack+0x10/0x14)
> [<c02123f8>] (show_stack) from [<c070141c>] (dump_stack+0x70/0xbc)
> [<c070141c>] (dump_stack) from [<c02f4cb0>] (__kmalloc+0x124/0x250)
> [<c02f4cb0>] (__kmalloc) from [<c05ab270>] (dev_pm_opp_init_cpufreq_table+0x3c/0x10c)
> [<c05ab270>] (dev_pm_opp_init_cpufreq_table) from [<bf000508>] (cpufreq_init+0x48/0x378 [cpufreq_generic])
> [<bf000508>] (cpufreq_init [cpufreq_generic]) from [<c05a9e08>] (__cpufreq_add_dev.isra.22+0x200/0x92c)
> [<c05a9e08>] (__cpufreq_add_dev.isra.22) from [<c050c160>] (subsys_interface_register+0x84/0xc8)
> [<c050c160>] (subsys_interface_register) from [<c05a9494>] (cpufreq_register_driver+0x108/0x2d8)
> [<c05a9494>] (cpufreq_register_driver) from [<bf000888>] (generic_cpufreq_probe+0x50/0x74 [cpufreq_generic])
> [<bf000888>] (generic_cpufreq_probe [cpufreq_generic]) from [<c050e994>] (platform_drv_probe+0x18/0x48)
> [<c050e994>] (platform_drv_probe) from [<c050d1f4>] (driver_probe_device+0x128/0x370)
> [<c050d1f4>] (driver_probe_device) from [<c050d4d0>] (__driver_attach+0x94/0x98)
> [<c050d4d0>] (__driver_attach) from [<c050b778>] (bus_for_each_dev+0x54/0x88)
> [<c050b778>] (bus_for_each_dev) from [<c050c894>] (bus_add_driver+0xe8/0x204)
> [<c050c894>] (bus_add_driver) from [<c050dd48>] (driver_register+0x78/0xf4)
> [<c050dd48>] (driver_register) from [<c0208870>] (do_one_initcall+0xac/0x1d8)
> [<c0208870>] (do_one_initcall) from [<c028b6b4>] (load_module+0x190c/0x21e8)
> [<c028b6b4>] (load_module) from [<c028c034>] (SyS_init_module+0xa4/0x110)
> [<c028c034>] (SyS_init_module) from [<c020f0c0>] (ret_fast_syscall+0x0/0x48)
>
> Fixes: a0dd7b79657b "PM / OPP: Move cpufreq specific OPP functions out of generic OPP library"

That looks to be wrong. This commit just moved things around and I can still
see rcu_read_lock() before this commit.

> Cc: Kevin Hilman <khilman@xxxxxxxxxxxxxxxxxxx>
> Cc: Nishanth Menon <nm@xxxxxx>
> Signed-off-by: Stephen Boyd <sboyd@xxxxxxxxxxxxxx>
> ---
>
> It would be nice to not do atomic allocations, but I guess the table could
> change size?

Yep. Number of OPPs can vary over time on a running machine.

>  drivers/cpufreq/cpufreq_opp.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/drivers/cpufreq/cpufreq_opp.c b/drivers/cpufreq/cpufreq_opp.c
> index c0c6f4a4eccf..f7a32d2326c6 100644
> --- a/drivers/cpufreq/cpufreq_opp.c
> +++ b/drivers/cpufreq/cpufreq_opp.c
> @@ -60,7 +60,7 @@ int dev_pm_opp_init_cpufreq_table(struct device *dev,
>                 goto out;
>         }
>
> -       freq_table = kzalloc(sizeof(*freq_table) * (max_opps + 1), GFP_KERNEL);
> +       freq_table = kcalloc(sizeof(*freq_table), (max_opps + 1), GFP_ATOMIC);

I am not really sure if there would be any consequences of this, but overall it
looks fine.

Acked-by: Viresh Kumar <viresh.kumar@xxxxxxxxxx>
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