Date:	Fri, 30 Mar 2007 12:09:03 +0400
From:	Alexey Dobriyan <adobriyan@...ru>
To:	Andrew Morton <akpm@...ux-foundation.org>,
	Mattia Dongili <malattia@...ux.it>
Cc:	Greg KH <gregkh@...e.de>, Dave Jones <davej@...hat.com>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] fix cpufreq_stats attrs removal

On Thu, Mar 22, 2007 at 06:02:01PM +0100, Mattia Dongili wrote:
> On Wed, Mar 21, 2007 at 08:10:42PM -0800, Andrew Morton wrote:
> > I ain't picky, but as a short-term thing it'd be kinda nice if it didn't
> > oops the kernel.
> 
> There are other symptoms to this same bug:
> 
> 1. unload p4-clockmod: /sys/.../cpu0/cpufreq is removed all together
> 2. load p4-clockmod: /sys/.../cpu0/cpufreq appears but no 'stats' subdir
>    (yes, cpufreq_stats is loaded)
> 3. rmmod cpufreq_stats: Ooops!
> 
> Call Trace:
>  [<c0183f5b>] remove_dir+0x33/0xc4
>  [<c0184fca>] remove_files+0x1a/0x28
>  [<c018503b>] sysfs_remove_group+0x63/0x71
>  [<f898c38d>] cpufreq_stat_cpu_callback+0x51/0x8a [cpufreq_stats]
>  [<f898c477>] cpufreq_stats_exit+0x47/0x4b [cpufreq_stats]
>  [<c012f145>] sys_delete_module+0x190/0x1b7
>  [<c0140073>] do_wp_page+0x231/0x3e7
>  [<c0102e17>] syscall_call+0x7/0xb
> 
> The problem is cpufreq_stats doesn't know when a cpufreq driver is
> removed and doesn't cleanup. I guess this affects any setup with
> cpufreq_stats.
> The attached patch seems to solve both symptoms and yes... it's quite
> invasive as it introduce one more cpufreq policy notification (REMOVED).
> 
> BTW: the patch is against .21-rc4-mm1 but applies with some fuzz to
> 2.6.20 too

Also, it doesn't work.

/sys/*/cpufreq/stats dir stays if you cd into it _before_ rmmod.

	# modprobe p4-clockmod
	$ /sys/devices/system/cpu/cpu0/cpufreq/stats
	# rmmod p4-clockmod
	$ cat time_in_state

p4-clockmod: P4/Xeon(TM) CPU On-Demand Clock Modulation available
BUG: unable to handle kernel paging request at virtual address 6b6b6b6f
 printing eip:
c01955e1
*pde = 00000000
Oops: 0000 [#1]
last sysfs file: devices/system/cpu/cpu0/cpufreq/stats/time_in_state
Modules linked in: speedstep_lib ohci_hcd af_packet e1000 ehci_hcd uhci_hcd usbcore
CPU:    0
EIP:    0060:[<c01955e1>]    Not tainted VLI
EFLAGS: 00010202   (2.6.21-rc5-mm1 #2)
EIP is at sysfs_open_file+0xb6/0x26f
eax: 6b6b6b6b   ebx: c03b3cb0   ecx: 00000000   edx: f732772c
esi: 00000000   edi: c0681400   ebp: f36fad10   esp: f3595ee0
ds: 007b   es: 007b   fs: 00d8  gs: 0033  ss: 0068
Process cat (pid: 7545, ti=f3594000 task=f3773510 task.ti=f3594000)
Stack: 00001000 f376f26c f732772c f376f26c f36fad10 f376f26c f3595f38 c019552b 
       c015ced8 c18d3190 f3746a18 f36fad10 00008000 f3595f38 ffffff9c c015d052 
       f36fad10 00000000 00000000 c015d094 00000000 f3595f38 f3746a18 c18d3190 
Call Trace:
 [<c019552b>] sysfs_open_file+0x0/0x26f
 [<c015ced8>] __dentry_open+0xa4/0x191
 [<c015d052>] nameidata_to_filp+0x31/0x3a
 [<c015d094>] do_filp_open+0x39/0x40
 [<c015ce23>] get_unused_fd+0xa1/0xb2
 [<c02db41f>] _spin_unlock+0x14/0x1c
 [<c015ce23>] get_unused_fd+0xa1/0xb2
 [<c015d0d5>] do_sys_open+0x3a/0x6d
 [<c015d143>] sys_open+0x1c/0x20
 [<c0103c96>] sysenter_past_esp+0x5f/0x99
 =======================
INFO: lockdep is turned off.
Code: 0f 85 24 01 00 00 8b 43 04 85 c0 74 0f 83 38 02 0f 84 c4 01 00 00 ff 80 80 01 00 00 8b 54 24 08 8b 42 28 85 c0 0f 84 62 01 00 00 <8b> 40 04 85 c0 0f 84 57 01 00 00 8b 40 04 89 44 24 0c 8b 74 24 
EIP: [<c01955e1>] sysfs_open_file+0xb6/0x26f SS:ESP 0068:f3595ee0
Slab corruption: start=f73276e0, len=256
Redzone: 0x5a2cf071/0x5a2cf071.
Last user: [<c0185810>](load_elf_binary+0xa79/0x1a19)
060: 6b 6b 6b 6b 6c 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b
Prev obj: start=f73275d4, len=256
Redzone: 0x5a2cf071/0x5a2cf071.
Last user: [<c01864fb>](load_elf_binary+0x1764/0x1a19)
000: 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b
010: 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b
Next obj: start=f73277ec, len=256
Redzone: 0x5a2cf071/0x5a2cf071.
Last user: [<c01864fb>](load_elf_binary+0x1764/0x1a19)
000: 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b
010: 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b

> --- linux-2.6.20/drivers/cpufreq/cpufreq.c	2007-03-22 17:00:38.000000000 +0100
> +++ linux-2.6.20.dirty/drivers/cpufreq/cpufreq.c	2007-03-22 16:51:09.000000000 +0100
> @@ -989,6 +989,10 @@ static int __cpufreq_remove_dev (struct 
>  
>  	unlock_policy_rwsem_write(cpu);
>  
> +	/* notify of policy cancellation */
> +	blocking_notifier_call_chain(&cpufreq_policy_notifier_list,
> +			CPUFREQ_REMOVE, data);
> +
>  	kobject_unregister(&data->kobj);
>  
>  	kobject_put(&data->kobj);
> diff -rup linux-2.6.20/drivers/cpufreq/cpufreq_stats.c linux-2.6.20.dirty/drivers/cpufreq/cpufreq_stats.c
> --- linux-2.6.20/drivers/cpufreq/cpufreq_stats.c	2007-03-22 17:00:38.000000000 +0100
> +++ linux-2.6.20.dirty/drivers/cpufreq/cpufreq_stats.c	2007-03-22 17:06:24.000000000 +0100
> @@ -257,18 +257,23 @@ static int
>  cpufreq_stat_notifier_policy (struct notifier_block *nb, unsigned long val,
>  		void *data)
>  {
> -	int ret;
> +	int ret = 0;
>  	struct cpufreq_policy *policy = data;
>  	struct cpufreq_frequency_table *table;
>  	unsigned int cpu = policy->cpu;
> -	if (val != CPUFREQ_NOTIFY)
> -		return 0;
> -	table = cpufreq_frequency_get_table(cpu);
> -	if (!table)
> -		return 0;
> -	if ((ret = cpufreq_stats_create_table(policy, table)))
> -		return ret;
> -	return 0;
> +	switch (val) {
> +	case CPUFREQ_NOTIFY:
> +		table = cpufreq_frequency_get_table(cpu);
> +		if (!table)
> +			break;
> +		ret = cpufreq_stats_create_table(policy, table);
> +		break;
> +
> +	case CPUFREQ_REMOVE:
> +		cpufreq_stats_free_table(cpu);
> +		break;
> +	}
> +	return ret;
>  }
>  
>  static int
> @@ -371,8 +376,7 @@ __exit cpufreq_stats_exit(void)
>  			CPUFREQ_TRANSITION_NOTIFIER);
>  	unregister_hotcpu_notifier(&cpufreq_stat_cpu_notifier);
>  	for_each_online_cpu(cpu) {
> -		cpufreq_stat_cpu_callback(&cpufreq_stat_cpu_notifier,
> -						CPU_DEAD, (void *)(long)cpu);
> +		cpufreq_stats_free_table(cpu);
>  	}
>  }
>  
> --- linux-2.6.20/include/linux/cpufreq.h	2007-03-22 17:00:47.000000000 +0100
> +++ linux-2.6.20.dirty/include/linux/cpufreq.h	2007-03-22 16:10:37.000000000 +0100
> @@ -96,6 +96,7 @@ struct cpufreq_policy {
>  #define CPUFREQ_ADJUST		(0)
>  #define CPUFREQ_INCOMPATIBLE	(1)
>  #define CPUFREQ_NOTIFY		(2)
> +#define CPUFREQ_REMOVE		(3)
>  
>  #define CPUFREQ_SHARED_TYPE_NONE (0) /* None */
>  #define CPUFREQ_SHARED_TYPE_HW	 (1) /* HW does needed coordination */

-
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