Re: [PATCH 2/2] cgroup: remove subsystem files when remounting cgroup

2012-12-02 Thread Gao feng 
Hello Tejun

on 2012/12/01 03:27, Tejun Heo wrote:
> Hello, Gao.
> 
> On Sat, Dec 01, 2012 at 12:21:29AM +0800, Gao feng wrote:
>> cgroup_clear_directroy is called by cgroup_d_remove_dir
>> and cgroup_remount.
>>
>> when we call cgroup_remount to remount the cgroup,the subsystem
>> may be unlinked from cgroupfs_root->subsys_list in rebind_subsystem,this
>> subsystem's files will not be removed in cgroup_clear_directroy.
>> And the system will panic when we try to access these files.
>>
>> this patch fix it.
> 
> I'd really appreciated if you explain how it's fixed.
> 
>> Signed-off-by: Gao feng 
>> ---
>>  kernel/cgroup.c |   86 
>> ++
>>  1 files changed, 54 insertions(+), 32 deletions(-)
>>
>> diff --git a/kernel/cgroup.c b/kernel/cgroup.c
>> index e5233b7..90429d5 100644
>> --- a/kernel/cgroup.c
>> +++ b/kernel/cgroup.c
>> @@ -982,10 +982,14 @@ static void cgroup_clear_directory(struct dentry *dir, 
>> bool base_files,
>> unsigned long subsys_mask)
>>  {
>>  struct cgroup *cgrp = __d_cgrp(dir);
>> -struct cgroup_subsys *ss;
>> +int i;
>>  
>> -for_each_subsys(cgrp->root, ss) {
>> +for (i = 0; i < CGROUP_SUBSYS_COUNT; i++) {
>>  struct cftype_set *set;
>> +struct cgroup_subsys *ss = subsys[i];
>> +
>> +if (ss == NULL)
>> +continue;
> 
> Ummm... I can't say I like it.  It tries to work around the problem
> that the backing subsys may go away earlier by changing how the
> subsystems are iterated so that the "gone" subsystems can be iterated,
> which really doesn't seem like a good diea.  I mean, what if somebody
> tries to access the files inbetween?  root_cgrp->subsys[] would be
> %NULL and segfault all the same.
> 

Yes,You are right.I didn't consider this problem.

>>  static void drop_parsed_module_refcounts(unsigned long subsys_mask)
>> @@ -1392,23 +1403,34 @@ static int cgroup_remount(struct super_block *sb, 
>> int *flags, char *data)
>>  removed_mask = root->subsys_mask & ~opts.subsys_mask;
>>  
>>  /* Don't allow flags or name to change at remount */
>> +ret = -EINVAL;
>>  if (opts.flags != root->flags ||
>>  (opts.name && strcmp(opts.name, root->name))) {
>> -ret = -EINVAL;
>>  drop_parsed_module_refcounts(opts.subsys_mask);
>>  goto out_unlock;
>>  }
>>  
>> -ret = rebind_subsystems(root, opts.subsys_mask);
>> +/*
>> + * Add the reference of these removed subsystem,we
>> + * need use subsystems to remove their cgroup files.
>> + */
>> +ret = cgroup_get_module_refcounts(removed_mask);
>>  if (ret) {
>>  drop_parsed_module_refcounts(opts.subsys_mask);
>>  goto out_unlock;
>>  }
>>  
>> +ret = rebind_subsystems(root, opts.subsys_mask);
>> +if (ret) {
>> +drop_parsed_module_refcounts(opts.subsys_mask | removed_mask);
>> +goto out_unlock;
>> +}
>> +
>>  /* clear out any existing files and repopulate subsystem files */
>>  cgroup_clear_directory(cgrp->dentry, false, removed_mask);
>>  /* re-populate subsystem files */
>>  cgroup_populate_dir(cgrp, false, added_mask);
>> +drop_parsed_module_refcounts(removed_mask);
> 
> So, how about performing cgroup_clear_directory() *before*
> rebind_subsystems() and then restore it afterwards?
> 

Get it,will fix this problem as you said.

Thanks!

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Re: [PATCH 2/2] cgroup: remove subsystem files when remounting cgroup

2012-12-02 Thread Gao feng 
Hello Tejun

on 2012/12/01 03:27, Tejun Heo wrote:
 Hello, Gao.
 
 On Sat, Dec 01, 2012 at 12:21:29AM +0800, Gao feng wrote:
 cgroup_clear_directroy is called by cgroup_d_remove_dir
 and cgroup_remount.

 when we call cgroup_remount to remount the cgroup,the subsystem
 may be unlinked from cgroupfs_root-subsys_list in rebind_subsystem,this
 subsystem's files will not be removed in cgroup_clear_directroy.
 And the system will panic when we try to access these files.

 this patch fix it.
 
 I'd really appreciated if you explain how it's fixed.
 
 Signed-off-by: Gao feng gaof...@cn.fujitsu.com
 ---
  kernel/cgroup.c |   86 
 ++
  1 files changed, 54 insertions(+), 32 deletions(-)

 diff --git a/kernel/cgroup.c b/kernel/cgroup.c
 index e5233b7..90429d5 100644
 --- a/kernel/cgroup.c
 +++ b/kernel/cgroup.c
 @@ -982,10 +982,14 @@ static void cgroup_clear_directory(struct dentry *dir, 
 bool base_files,
 unsigned long subsys_mask)
  {
  struct cgroup *cgrp = __d_cgrp(dir);
 -struct cgroup_subsys *ss;
 +int i;
  
 -for_each_subsys(cgrp-root, ss) {
 +for (i = 0; i  CGROUP_SUBSYS_COUNT; i++) {
  struct cftype_set *set;
 +struct cgroup_subsys *ss = subsys[i];
 +
 +if (ss == NULL)
 +continue;
 
 Ummm... I can't say I like it.  It tries to work around the problem
 that the backing subsys may go away earlier by changing how the
 subsystems are iterated so that the gone subsystems can be iterated,
 which really doesn't seem like a good diea.  I mean, what if somebody
 tries to access the files inbetween?  root_cgrp-subsys[] would be
 %NULL and segfault all the same.
 

Yes,You are right.I didn't consider this problem.

  static void drop_parsed_module_refcounts(unsigned long subsys_mask)
 @@ -1392,23 +1403,34 @@ static int cgroup_remount(struct super_block *sb, 
 int *flags, char *data)
  removed_mask = root-subsys_mask  ~opts.subsys_mask;
  
  /* Don't allow flags or name to change at remount */
 +ret = -EINVAL;
  if (opts.flags != root-flags ||
  (opts.name  strcmp(opts.name, root-name))) {
 -ret = -EINVAL;
  drop_parsed_module_refcounts(opts.subsys_mask);
  goto out_unlock;
  }
  
 -ret = rebind_subsystems(root, opts.subsys_mask);
 +/*
 + * Add the reference of these removed subsystem,we
 + * need use subsystems to remove their cgroup files.
 + */
 +ret = cgroup_get_module_refcounts(removed_mask);
  if (ret) {
  drop_parsed_module_refcounts(opts.subsys_mask);
  goto out_unlock;
  }
  
 +ret = rebind_subsystems(root, opts.subsys_mask);
 +if (ret) {
 +drop_parsed_module_refcounts(opts.subsys_mask | removed_mask);
 +goto out_unlock;
 +}
 +
  /* clear out any existing files and repopulate subsystem files */
  cgroup_clear_directory(cgrp-dentry, false, removed_mask);
  /* re-populate subsystem files */
  cgroup_populate_dir(cgrp, false, added_mask);
 +drop_parsed_module_refcounts(removed_mask);
 
 So, how about performing cgroup_clear_directory() *before*
 rebind_subsystems() and then restore it afterwards?
 

Get it,will fix this problem as you said.

Thanks!

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Re: [PATCH 2/2] cgroup: remove subsystem files when remounting cgroup

2012-11-30 Thread Tejun Heo 
Hello, Gao.

On Sat, Dec 01, 2012 at 12:21:29AM +0800, Gao feng wrote:
> cgroup_clear_directroy is called by cgroup_d_remove_dir
> and cgroup_remount.
> 
> when we call cgroup_remount to remount the cgroup,the subsystem
> may be unlinked from cgroupfs_root->subsys_list in rebind_subsystem,this
> subsystem's files will not be removed in cgroup_clear_directroy.
> And the system will panic when we try to access these files.
> 
> this patch fix it.

I'd really appreciated if you explain how it's fixed.

> Signed-off-by: Gao feng 
> ---
>  kernel/cgroup.c |   86 ++
>  1 files changed, 54 insertions(+), 32 deletions(-)
> 
> diff --git a/kernel/cgroup.c b/kernel/cgroup.c
> index e5233b7..90429d5 100644
> --- a/kernel/cgroup.c
> +++ b/kernel/cgroup.c
> @@ -982,10 +982,14 @@ static void cgroup_clear_directory(struct dentry *dir, 
> bool base_files,
>  unsigned long subsys_mask)
>  {
>   struct cgroup *cgrp = __d_cgrp(dir);
> - struct cgroup_subsys *ss;
> + int i;
>  
> - for_each_subsys(cgrp->root, ss) {
> + for (i = 0; i < CGROUP_SUBSYS_COUNT; i++) {
>   struct cftype_set *set;
> + struct cgroup_subsys *ss = subsys[i];
> +
> + if (ss == NULL)
> + continue;

Ummm... I can't say I like it.  It tries to work around the problem
that the backing subsys may go away earlier by changing how the
subsystems are iterated so that the "gone" subsystems can be iterated,
which really doesn't seem like a good diea.  I mean, what if somebody
tries to access the files inbetween?  root_cgrp->subsys[] would be
%NULL and segfault all the same.

>  static void drop_parsed_module_refcounts(unsigned long subsys_mask)
> @@ -1392,23 +1403,34 @@ static int cgroup_remount(struct super_block *sb, int 
> *flags, char *data)
>   removed_mask = root->subsys_mask & ~opts.subsys_mask;
>  
>   /* Don't allow flags or name to change at remount */
> + ret = -EINVAL;
>   if (opts.flags != root->flags ||
>   (opts.name && strcmp(opts.name, root->name))) {
> - ret = -EINVAL;
>   drop_parsed_module_refcounts(opts.subsys_mask);
>   goto out_unlock;
>   }
>  
> - ret = rebind_subsystems(root, opts.subsys_mask);
> + /*
> +  * Add the reference of these removed subsystem,we
> +  * need use subsystems to remove their cgroup files.
> +  */
> + ret = cgroup_get_module_refcounts(removed_mask);
>   if (ret) {
>   drop_parsed_module_refcounts(opts.subsys_mask);
>   goto out_unlock;
>   }
>  
> + ret = rebind_subsystems(root, opts.subsys_mask);
> + if (ret) {
> + drop_parsed_module_refcounts(opts.subsys_mask | removed_mask);
> + goto out_unlock;
> + }
> +
>   /* clear out any existing files and repopulate subsystem files */
>   cgroup_clear_directory(cgrp->dentry, false, removed_mask);
>   /* re-populate subsystem files */
>   cgroup_populate_dir(cgrp, false, added_mask);
> + drop_parsed_module_refcounts(removed_mask);

So, how about performing cgroup_clear_directory() *before*
rebind_subsystems() and then restore it afterwards?

Thanks.

-- 
tejun
--
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Please read the FAQ at  http://www.tux.org/lkml/

[PATCH 2/2] cgroup: remove subsystem files when remounting cgroup

2012-11-30 Thread Gao feng 
cgroup_clear_directroy is called by cgroup_d_remove_dir
and cgroup_remount.

when we call cgroup_remount to remount the cgroup,the subsystem
may be unlinked from cgroupfs_root->subsys_list in rebind_subsystem,this
subsystem's files will not be removed in cgroup_clear_directroy.
And the system will panic when we try to access these files.

this patch fix it.

Signed-off-by: Gao feng 
---
 kernel/cgroup.c |   86 ++
 1 files changed, 54 insertions(+), 32 deletions(-)

diff --git a/kernel/cgroup.c b/kernel/cgroup.c
index e5233b7..90429d5 100644
--- a/kernel/cgroup.c
+++ b/kernel/cgroup.c
@@ -982,10 +982,14 @@ static void cgroup_clear_directory(struct dentry *dir, 
bool base_files,
   unsigned long subsys_mask)
 {
struct cgroup *cgrp = __d_cgrp(dir);
-   struct cgroup_subsys *ss;
+   int i;
 
-   for_each_subsys(cgrp->root, ss) {
+   for (i = 0; i < CGROUP_SUBSYS_COUNT; i++) {
struct cftype_set *set;
+   struct cgroup_subsys *ss = subsys[i];
+
+   if (ss == NULL)
+   continue;
if (!test_bit(ss->subsys_id, _mask))
continue;
list_for_each_entry(set, >cftsets, node)
@@ -1160,6 +1164,40 @@ static int cgroup_show_options(struct seq_file *seq, 
struct dentry *dentry)
return 0;
 }
 
+static int cgroup_get_module_refcounts(unsigned long subsys_mask)
+{
+   int i;
+   bool module_pin_failed = false;
+
+   for (i = 0; i < CGROUP_SUBSYS_COUNT; i++) {
+   unsigned long bit = 1UL << i;
+
+   if (!(bit & subsys_mask))
+   continue;
+   if (!try_module_get(subsys[i]->module)) {
+   module_pin_failed = true;
+   break;
+   }
+   }
+   if (module_pin_failed) {
+   /*
+* oops, one of the modules was going away. this means that we
+* raced with a module_delete call, and to the user this is
+* essentially a "subsystem doesn't exist" case.
+*/
+   for (i--; i >= 0; i--) {
+   /* drop refcounts only on the ones we took */
+   unsigned long bit = 1UL << i;
+
+   if (!(bit & subsys_mask))
+   continue;
+   module_put(subsys[i]->module);
+   }
+   return -ENOENT;
+   }
+   return 0;
+}
+
 struct cgroup_sb_opts {
unsigned long subsys_mask;
unsigned long flags;
@@ -1185,7 +1223,6 @@ static int parse_cgroupfs_options(char *data, struct 
cgroup_sb_opts *opts)
bool all_ss = false, one_ss = false;
unsigned long mask = (unsigned long)-1;
int i;
-   bool module_pin_failed = false;
 
BUG_ON(!mutex_is_locked(_mutex));
 
@@ -1324,34 +1361,8 @@ static int parse_cgroupfs_options(char *data, struct 
cgroup_sb_opts *opts)
 * take duplicate reference counts on a subsystem that's already used,
 * but rebind_subsystems handles this case.
 */
-   for (i = 0; i < CGROUP_SUBSYS_COUNT; i++) {
-   unsigned long bit = 1UL << i;
 
-   if (!(bit & opts->subsys_mask))
-   continue;
-   if (!try_module_get(subsys[i]->module)) {
-   module_pin_failed = true;
-   break;
-   }
-   }
-   if (module_pin_failed) {
-   /*
-* oops, one of the modules was going away. this means that we
-* raced with a module_delete call, and to the user this is
-* essentially a "subsystem doesn't exist" case.
-*/
-   for (i--; i >= 0; i--) {
-   /* drop refcounts only on the ones we took */
-   unsigned long bit = 1UL << i;
-
-   if (!(bit & opts->subsys_mask))
-   continue;
-   module_put(subsys[i]->module);
-   }
-   return -ENOENT;
-   }
-
-   return 0;
+   return cgroup_get_module_refcounts(opts->subsys_mask);
 }
 
 static void drop_parsed_module_refcounts(unsigned long subsys_mask)
@@ -1392,23 +1403,34 @@ static int cgroup_remount(struct super_block *sb, int 
*flags, char *data)
removed_mask = root->subsys_mask & ~opts.subsys_mask;
 
/* Don't allow flags or name to change at remount */
+   ret = -EINVAL;
if (opts.flags != root->flags ||
(opts.name && strcmp(opts.name, root->name))) {
-   ret = -EINVAL;
drop_parsed_module_refcounts(opts.subsys_mask);
goto out_unlock;
}
 
-   ret = rebind_subsystems(root, opts.subsys_mask);
+   /*
+* Add the reference of these removed subsystem,we
+

[PATCH 2/2] cgroup: remove subsystem files when remounting cgroup

2012-11-30 Thread Gao feng 
cgroup_clear_directroy is called by cgroup_d_remove_dir
and cgroup_remount.

when we call cgroup_remount to remount the cgroup,the subsystem
may be unlinked from cgroupfs_root-subsys_list in rebind_subsystem,this
subsystem's files will not be removed in cgroup_clear_directroy.
And the system will panic when we try to access these files.

this patch fix it.

Signed-off-by: Gao feng gaof...@cn.fujitsu.com
---
 kernel/cgroup.c |   86 ++
 1 files changed, 54 insertions(+), 32 deletions(-)

diff --git a/kernel/cgroup.c b/kernel/cgroup.c
index e5233b7..90429d5 100644
--- a/kernel/cgroup.c
+++ b/kernel/cgroup.c
@@ -982,10 +982,14 @@ static void cgroup_clear_directory(struct dentry *dir, 
bool base_files,
   unsigned long subsys_mask)
 {
struct cgroup *cgrp = __d_cgrp(dir);
-   struct cgroup_subsys *ss;
+   int i;
 
-   for_each_subsys(cgrp-root, ss) {
+   for (i = 0; i  CGROUP_SUBSYS_COUNT; i++) {
struct cftype_set *set;
+   struct cgroup_subsys *ss = subsys[i];
+
+   if (ss == NULL)
+   continue;
if (!test_bit(ss-subsys_id, subsys_mask))
continue;
list_for_each_entry(set, ss-cftsets, node)
@@ -1160,6 +1164,40 @@ static int cgroup_show_options(struct seq_file *seq, 
struct dentry *dentry)
return 0;
 }
 
+static int cgroup_get_module_refcounts(unsigned long subsys_mask)
+{
+   int i;
+   bool module_pin_failed = false;
+
+   for (i = 0; i  CGROUP_SUBSYS_COUNT; i++) {
+   unsigned long bit = 1UL  i;
+
+   if (!(bit  subsys_mask))
+   continue;
+   if (!try_module_get(subsys[i]-module)) {
+   module_pin_failed = true;
+   break;
+   }
+   }
+   if (module_pin_failed) {
+   /*
+* oops, one of the modules was going away. this means that we
+* raced with a module_delete call, and to the user this is
+* essentially a subsystem doesn't exist case.
+*/
+   for (i--; i = 0; i--) {
+   /* drop refcounts only on the ones we took */
+   unsigned long bit = 1UL  i;
+
+   if (!(bit  subsys_mask))
+   continue;
+   module_put(subsys[i]-module);
+   }
+   return -ENOENT;
+   }
+   return 0;
+}
+
 struct cgroup_sb_opts {
unsigned long subsys_mask;
unsigned long flags;
@@ -1185,7 +1223,6 @@ static int parse_cgroupfs_options(char *data, struct 
cgroup_sb_opts *opts)
bool all_ss = false, one_ss = false;
unsigned long mask = (unsigned long)-1;
int i;
-   bool module_pin_failed = false;
 
BUG_ON(!mutex_is_locked(cgroup_mutex));
 
@@ -1324,34 +1361,8 @@ static int parse_cgroupfs_options(char *data, struct 
cgroup_sb_opts *opts)
 * take duplicate reference counts on a subsystem that's already used,
 * but rebind_subsystems handles this case.
 */
-   for (i = 0; i  CGROUP_SUBSYS_COUNT; i++) {
-   unsigned long bit = 1UL  i;
 
-   if (!(bit  opts-subsys_mask))
-   continue;
-   if (!try_module_get(subsys[i]-module)) {
-   module_pin_failed = true;
-   break;
-   }
-   }
-   if (module_pin_failed) {
-   /*
-* oops, one of the modules was going away. this means that we
-* raced with a module_delete call, and to the user this is
-* essentially a subsystem doesn't exist case.
-*/
-   for (i--; i = 0; i--) {
-   /* drop refcounts only on the ones we took */
-   unsigned long bit = 1UL  i;
-
-   if (!(bit  opts-subsys_mask))
-   continue;
-   module_put(subsys[i]-module);
-   }
-   return -ENOENT;
-   }
-
-   return 0;
+   return cgroup_get_module_refcounts(opts-subsys_mask);
 }
 
 static void drop_parsed_module_refcounts(unsigned long subsys_mask)
@@ -1392,23 +1403,34 @@ static int cgroup_remount(struct super_block *sb, int 
*flags, char *data)
removed_mask = root-subsys_mask  ~opts.subsys_mask;
 
/* Don't allow flags or name to change at remount */
+   ret = -EINVAL;
if (opts.flags != root-flags ||
(opts.name  strcmp(opts.name, root-name))) {
-   ret = -EINVAL;
drop_parsed_module_refcounts(opts.subsys_mask);
goto out_unlock;
}
 
-   ret = rebind_subsystems(root, opts.subsys_mask);
+   /*
+* Add the reference of these removed subsystem,we
+

Re: [PATCH 2/2] cgroup: remove subsystem files when remounting cgroup

2012-11-30 Thread Tejun Heo 
Hello, Gao.

On Sat, Dec 01, 2012 at 12:21:29AM +0800, Gao feng wrote:
 cgroup_clear_directroy is called by cgroup_d_remove_dir
 and cgroup_remount.
 
 when we call cgroup_remount to remount the cgroup,the subsystem
 may be unlinked from cgroupfs_root-subsys_list in rebind_subsystem,this
 subsystem's files will not be removed in cgroup_clear_directroy.
 And the system will panic when we try to access these files.
 
 this patch fix it.

I'd really appreciated if you explain how it's fixed.

 Signed-off-by: Gao feng gaof...@cn.fujitsu.com
 ---
  kernel/cgroup.c |   86 ++
  1 files changed, 54 insertions(+), 32 deletions(-)
 
 diff --git a/kernel/cgroup.c b/kernel/cgroup.c
 index e5233b7..90429d5 100644
 --- a/kernel/cgroup.c
 +++ b/kernel/cgroup.c
 @@ -982,10 +982,14 @@ static void cgroup_clear_directory(struct dentry *dir, 
 bool base_files,
  unsigned long subsys_mask)
  {
   struct cgroup *cgrp = __d_cgrp(dir);
 - struct cgroup_subsys *ss;
 + int i;
  
 - for_each_subsys(cgrp-root, ss) {
 + for (i = 0; i  CGROUP_SUBSYS_COUNT; i++) {
   struct cftype_set *set;
 + struct cgroup_subsys *ss = subsys[i];
 +
 + if (ss == NULL)
 + continue;

Ummm... I can't say I like it.  It tries to work around the problem
that the backing subsys may go away earlier by changing how the
subsystems are iterated so that the gone subsystems can be iterated,
which really doesn't seem like a good diea.  I mean, what if somebody
tries to access the files inbetween?  root_cgrp-subsys[] would be
%NULL and segfault all the same.

  static void drop_parsed_module_refcounts(unsigned long subsys_mask)
 @@ -1392,23 +1403,34 @@ static int cgroup_remount(struct super_block *sb, int 
 *flags, char *data)
   removed_mask = root-subsys_mask  ~opts.subsys_mask;
  
   /* Don't allow flags or name to change at remount */
 + ret = -EINVAL;
   if (opts.flags != root-flags ||
   (opts.name  strcmp(opts.name, root-name))) {
 - ret = -EINVAL;
   drop_parsed_module_refcounts(opts.subsys_mask);
   goto out_unlock;
   }
  
 - ret = rebind_subsystems(root, opts.subsys_mask);
 + /*
 +  * Add the reference of these removed subsystem,we
 +  * need use subsystems to remove their cgroup files.
 +  */
 + ret = cgroup_get_module_refcounts(removed_mask);
   if (ret) {
   drop_parsed_module_refcounts(opts.subsys_mask);
   goto out_unlock;
   }
  
 + ret = rebind_subsystems(root, opts.subsys_mask);
 + if (ret) {
 + drop_parsed_module_refcounts(opts.subsys_mask | removed_mask);
 + goto out_unlock;
 + }
 +
   /* clear out any existing files and repopulate subsystem files */
   cgroup_clear_directory(cgrp-dentry, false, removed_mask);
   /* re-populate subsystem files */
   cgroup_populate_dir(cgrp, false, added_mask);
 + drop_parsed_module_refcounts(removed_mask);

So, how about performing cgroup_clear_directory() *before*
rebind_subsystems() and then restore it afterwards?

Thanks.

-- 
tejun
--
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