On 18-10-16, 00:41, Sergey Senozhatsky wrote:
> 'best' is always less or equals to 'pos', so `best - pos' returns
> a negative value which is then getting casted to `unsigned int'
> and passed to __cpufreq_driver_target()->acpi_cpufreq_target()
> for policy->freq_table selection. This results in
> 
>  BUG: unable to handle kernel paging request at ffff881019b469f8
>  IP: [<ffffffffa00356c1>] acpi_cpufreq_target+0x4f/0x190 [acpi_cpufreq]
>  PGD 267f067
>  PUD 0
> 
>  Oops: 0000 [#1] PREEMPT SMP
>  CPU: 6 PID: 70 Comm: kworker/6:1 Not tainted 
> 4.9.0-rc1-next-20161017-dbg-dirty
>  Workqueue: events dbs_work_handler
>  task: ffff88041b808000 task.stack: ffff88041b810000
>  RIP: 0010:[<ffffffffa00356c1>]  [<ffffffffa00356c1>] 
> acpi_cpufreq_target+0x4f/0x190 [acpi_cpufreq]
>  RSP: 0018:ffff88041b813c60  EFLAGS: 00010282
>  RAX: ffff880419b46a00 RBX: ffff88041b848400 RCX: ffff880419b20f80
>  RDX: 00000000001dff38 RSI: 00000000ffffffff RDI: ffff88041b848400
>  RBP: ffff88041b813cb0 R08: 0000000000000006 R09: 0000000000000040
>  R10: ffffffff8207f9e0 R11: ffffffff8173595b R12: 0000000000000000
>  R13: ffff88041f1dff38 R14: 0000000000262900 R15: 0000000bfffffff4
>  FS:  0000000000000000(0000) GS:ffff88041f000000(0000) knlGS:0000000000000000
>  CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
>  CR2: ffff881019b469f8 CR3: 000000041a2d3000 CR4: 00000000001406e0
>  Stack:
>   ffff88041b813cb0 ffffffff813347f9 ffff88041b813ca0 ffffffff81334663
>   ffff88041f1d4bc0 ffff88041b848400 0000000000000000 0000000000000000
>   0000000000262900 0000000000000000 ffff88041b813d00 ffffffff813355dc
>  Call Trace:
>   [<ffffffff813347f9>] ? cpufreq_freq_transition_begin+0xf1/0xfc
>   [<ffffffff81334663>] ? get_cpu_idle_time+0x97/0xa6
>   [<ffffffff813355dc>] __cpufreq_driver_target+0x3b6/0x44e
>   [<ffffffff81336ca3>] cs_dbs_timer+0x11a/0x135
>   [<ffffffff81336fda>] dbs_work_handler+0x39/0x62
>   [<ffffffff81057823>] process_one_work+0x280/0x4a5
>   [<ffffffff81058719>] worker_thread+0x24f/0x397
>   [<ffffffff810584ca>] ? rescuer_thread+0x30b/0x30b
>   [<ffffffff81418380>] ? nl80211_get_key+0x29/0x36a
>   [<ffffffff8105d2b7>] kthread+0xfc/0x104
>   [<ffffffff8107ceea>] ? put_lock_stats.isra.9+0xe/0x20
>   [<ffffffff8105d1bb>] ? kthread_create_on_node+0x3f/0x3f
>   [<ffffffff814b2092>] ret_from_fork+0x22/0x30
>  Code: 56 4d 6b ff 0c 41 55 41 54 53 48 83 ec 28 48 8b 15 ad 1e 00 00 44 8b 41
>  08 48 8b 87 c8 00 00 00 49 89 d5 4e 03 2c c5 80 b2 78 81 <46> 8b 74 38 04 45
>  3b 75 00 75 11 31 c0 83 39 00 0f 84 1c 01 00
>  RIP  [<ffffffffa00356c1>] acpi_cpufreq_target+0x4f/0x190 [acpi_cpufreq]
>   RSP <ffff88041b813c60>
>  CR2: ffff881019b469f8
>  ---[ end trace 16d9fc7a17897d37 ]---
> 
> Signed-off-by: Sergey Senozhatsky <sergey.senozhat...@gmail.com>
> ---
>  include/linux/cpufreq.h | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/include/linux/cpufreq.h b/include/linux/cpufreq.h
> index 5fa55fc..32dc0cbd 100644
> --- a/include/linux/cpufreq.h
> +++ b/include/linux/cpufreq.h
> @@ -677,10 +677,10 @@ static inline int cpufreq_table_find_index_dl(struct 
> cpufreq_policy *policy,
>               if (best == table - 1)
>                       return pos - table;
>  
> -             return best - pos;
> +             return best - table;
>       }
>  
> -     return best - pos;
> +     return best - table;
>  }
>  

Acked-by: Viresh Kumar <viresh.ku...@linaro.org>

-- 
viresh

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