[v2] hugetlb_cgroup: fix imbalanced css_get and css_put pair for shared mappings
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Message ID 20210301120540.37076-1-linmiaohe@huawei.com
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Commit 7bb82127c8cff8abb745c674907fd69fdf81607e
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  • [v2] hugetlb_cgroup: fix imbalanced css_get and css_put pair for shared mappings
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Commit Message

Miaohe Lin March 1, 2021, 12:05 p.m. UTC
The current implementation of hugetlb_cgroup for shared mappings could have
different behavior. Consider the following two scenarios:

1.Assume initial css reference count of hugetlb_cgroup is 1:
  1.1 Call hugetlb_reserve_pages with from = 1, to = 2. So css reference
count is 2 associated with 1 file_region.
  1.2 Call hugetlb_reserve_pages with from = 2, to = 3. So css reference
count is 3 associated with 2 file_region.
  1.3 coalesce_file_region will coalesce these two file_regions into one.
So css reference count is 3 associated with 1 file_region now.

2.Assume initial css reference count of hugetlb_cgroup is 1 again:
  2.1 Call hugetlb_reserve_pages with from = 1, to = 3. So css reference
count is 2 associated with 1 file_region.

Therefore, we might have one file_region while holding one or more css
reference counts. This inconsistency could lead to imbalanced css_get()
and css_put() pair. If we do css_put one by one (i.g. hole punch case),
scenario 2 would put one more css reference. If we do css_put all together
(i.g. truncate case), scenario 1 will leak one css reference.

The imbalanced css_get() and css_put() pair would result in a non-zero
reference when we try to destroy the hugetlb cgroup. The hugetlb cgroup
directory is removed __but__ associated resource is not freed. This might
result in OOM or can not create a new hugetlb cgroup in a busy workload
ultimately.

In order to fix this, we have to make sure that one file_region must hold
and only hold one css reference. So in coalesce_file_region case, we should
release one css reference before coalescence. Also only put css reference
when the entire file_region is removed.

The last thing to note is that the caller of region_add() will only hold
one reference to h_cg->css for the whole contiguous reservation region.
But this area might be scattered when there are already some file_regions
reside in it. As a result, many file_regions may share only one h_cg->css
reference. In order to ensure that one file_region must hold and only hold
one h_cg->css reference, we should do css_get() for each file_region and
release the reference held by caller when they are done.

Fixes: 075a61d07a8e ("hugetlb_cgroup: add accounting for shared mappings")
Reported-by: kernel test robot <lkp@intel.com> (auto build test ERROR)
Signed-off-by: Miaohe Lin <linmiaohe@huawei.com>
Cc: stable@kernel.org
---
v1->v2:
	Fix auto build test ERROR when CGROUP_HUGETLB is disabled.
---
 include/linux/hugetlb_cgroup.h | 15 ++++++++++--
 mm/hugetlb.c                   | 42 ++++++++++++++++++++++++++++++----
 mm/hugetlb_cgroup.c            | 11 +++++++--
 3 files changed, 60 insertions(+), 8 deletions(-)

Comments

Mike Kravetz March 12, 2021, 7:09 p.m. UTC | #1
On 3/1/21 4:05 AM, Miaohe Lin wrote:
> The current implementation of hugetlb_cgroup for shared mappings could have
> different behavior. Consider the following two scenarios:
> 
> 1.Assume initial css reference count of hugetlb_cgroup is 1:
>   1.1 Call hugetlb_reserve_pages with from = 1, to = 2. So css reference
> count is 2 associated with 1 file_region.
>   1.2 Call hugetlb_reserve_pages with from = 2, to = 3. So css reference
> count is 3 associated with 2 file_region.
>   1.3 coalesce_file_region will coalesce these two file_regions into one.
> So css reference count is 3 associated with 1 file_region now.
> 
> 2.Assume initial css reference count of hugetlb_cgroup is 1 again:
>   2.1 Call hugetlb_reserve_pages with from = 1, to = 3. So css reference
> count is 2 associated with 1 file_region.
> 
> Therefore, we might have one file_region while holding one or more css
> reference counts. This inconsistency could lead to imbalanced css_get()
> and css_put() pair. If we do css_put one by one (i.g. hole punch case),
> scenario 2 would put one more css reference. If we do css_put all together
> (i.g. truncate case), scenario 1 will leak one css reference.
> 
> The imbalanced css_get() and css_put() pair would result in a non-zero
> reference when we try to destroy the hugetlb cgroup. The hugetlb cgroup
> directory is removed __but__ associated resource is not freed. This might
> result in OOM or can not create a new hugetlb cgroup in a busy workload
> ultimately.
> 
> In order to fix this, we have to make sure that one file_region must hold
> and only hold one css reference. So in coalesce_file_region case, we should

I think this would sound/read better if stated as:
... one file_region must hold exactly one css reference ...

This phrase is repeated in comments throughout the patch.

> release one css reference before coalescence. Also only put css reference
> when the entire file_region is removed.
> 
> The last thing to note is that the caller of region_add() will only hold
> one reference to h_cg->css for the whole contiguous reservation region.
> But this area might be scattered when there are already some file_regions
> reside in it. As a result, many file_regions may share only one h_cg->css
> reference. In order to ensure that one file_region must hold and only hold
> one h_cg->css reference, we should do css_get() for each file_region and
> release the reference held by caller when they are done.

Thanks for adding this to the commit message.

> 
> Fixes: 075a61d07a8e ("hugetlb_cgroup: add accounting for shared mappings")
> Reported-by: kernel test robot <lkp@intel.com> (auto build test ERROR)
> Signed-off-by: Miaohe Lin <linmiaohe@huawei.com>
> Cc: stable@kernel.org
> ---
> v1->v2:
> 	Fix auto build test ERROR when CGROUP_HUGETLB is disabled.
> ---
>  include/linux/hugetlb_cgroup.h | 15 ++++++++++--
>  mm/hugetlb.c                   | 42 ++++++++++++++++++++++++++++++----
>  mm/hugetlb_cgroup.c            | 11 +++++++--
>  3 files changed, 60 insertions(+), 8 deletions(-)

Just a few minor nits below, all in comments.  It is not required, but
would be nice to update these.  Code looks good.

Reviewed-by: Mike Kravetz <mike.kravetz@oracle.com>

> 
> diff --git a/include/linux/hugetlb_cgroup.h b/include/linux/hugetlb_cgroup.h
> index 2ad6e92f124a..0bff345c4bc6 100644
> --- a/include/linux/hugetlb_cgroup.h
> +++ b/include/linux/hugetlb_cgroup.h
> @@ -113,6 +113,11 @@ static inline bool hugetlb_cgroup_disabled(void)
>  	return !cgroup_subsys_enabled(hugetlb_cgrp_subsys);
>  }
>  
> +static inline void hugetlb_cgroup_put_rsvd_cgroup(struct hugetlb_cgroup *h_cg)
> +{
> +	css_put(&h_cg->css);
> +}
> +
>  extern int hugetlb_cgroup_charge_cgroup(int idx, unsigned long nr_pages,
>  					struct hugetlb_cgroup **ptr);
>  extern int hugetlb_cgroup_charge_cgroup_rsvd(int idx, unsigned long nr_pages,
> @@ -138,7 +143,8 @@ extern void hugetlb_cgroup_uncharge_counter(struct resv_map *resv,
>  
>  extern void hugetlb_cgroup_uncharge_file_region(struct resv_map *resv,
>  						struct file_region *rg,
> -						unsigned long nr_pages);
> +						unsigned long nr_pages,
> +						bool region_del);
>  
>  extern void hugetlb_cgroup_file_init(void) __init;
>  extern void hugetlb_cgroup_migrate(struct page *oldhpage,
> @@ -147,7 +153,8 @@ extern void hugetlb_cgroup_migrate(struct page *oldhpage,
>  #else
>  static inline void hugetlb_cgroup_uncharge_file_region(struct resv_map *resv,
>  						       struct file_region *rg,
> -						       unsigned long nr_pages)
> +						       unsigned long nr_pages,
> +						       bool region_del)
>  {
>  }
>  
> @@ -185,6 +192,10 @@ static inline bool hugetlb_cgroup_disabled(void)
>  	return true;
>  }
>  
> +static inline void hugetlb_cgroup_put_rsvd_cgroup(struct hugetlb_cgroup *h_cg)
> +{
> +}
> +
>  static inline int hugetlb_cgroup_charge_cgroup(int idx, unsigned long nr_pages,
>  					       struct hugetlb_cgroup **ptr)
>  {
> diff --git a/mm/hugetlb.c b/mm/hugetlb.c
> index 8fb42c6dd74b..87db91dff47f 100644
> --- a/mm/hugetlb.c
> +++ b/mm/hugetlb.c
> @@ -280,6 +280,18 @@ static void record_hugetlb_cgroup_uncharge_info(struct hugetlb_cgroup *h_cg,
>  		nrg->reservation_counter =
>  			&h_cg->rsvd_hugepage[hstate_index(h)];
>  		nrg->css = &h_cg->css;
> +		/*
> +		 * The caller (hugetlb_reserve_pages now) will only hold one

This can be called from other places such as alloc_huge_page.  Correct?
If so, we should drop the mention of hugetlb_reserve_pages.

> +		 * h_cg->css reference for the whole contiguous reservation
> +		 * region. But this area might be scattered when there are
> +		 * already some file_regions reside in it. As a result, many
> +		 * file_regions may share only one h_cg->css reference. In
> +		 * order to ensure that one file_region must hold and only
> +		 * hold one h_cg->css reference, we should do css_get for

... must hold exactly one ...

> +		 * each file_region and leave the reference held by caller
> +		 * untouched.
> +		 */
> +		css_get(&h_cg->css);
>  		if (!resv->pages_per_hpage)
>  			resv->pages_per_hpage = pages_per_huge_page(h);
>  		/* pages_per_hpage should be the same for all entries in
> @@ -293,6 +305,14 @@ static void record_hugetlb_cgroup_uncharge_info(struct hugetlb_cgroup *h_cg,
>  #endif
>  }
>  
> +static void put_uncharge_info(struct file_region *rg)
> +{
> +#ifdef CONFIG_CGROUP_HUGETLB
> +	if (rg->css)
> +		css_put(rg->css);
> +#endif
> +}
> +
>  static bool has_same_uncharge_info(struct file_region *rg,
>  				   struct file_region *org)
>  {
> @@ -316,6 +336,7 @@ static void coalesce_file_region(struct resv_map *resv, struct file_region *rg)
>  		prg->to = rg->to;
>  
>  		list_del(&rg->link);
> +		put_uncharge_info(rg);
>  		kfree(rg);
>  
>  		rg = prg;
> @@ -327,6 +348,7 @@ static void coalesce_file_region(struct resv_map *resv, struct file_region *rg)
>  		nrg->from = rg->from;
>  
>  		list_del(&rg->link);
> +		put_uncharge_info(rg);
>  		kfree(rg);
>  	}
>  }
> @@ -659,7 +681,7 @@ static long region_del(struct resv_map *resv, long f, long t)
>  
>  			del += t - f;
>  			hugetlb_cgroup_uncharge_file_region(
> -				resv, rg, t - f);
> +				resv, rg, t - f, false);
>  
>  			/* New entry for end of split region */
>  			nrg->from = t;
> @@ -680,7 +702,7 @@ static long region_del(struct resv_map *resv, long f, long t)
>  		if (f <= rg->from && t >= rg->to) { /* Remove entire region */
>  			del += rg->to - rg->from;
>  			hugetlb_cgroup_uncharge_file_region(resv, rg,
> -							    rg->to - rg->from);
> +							    rg->to - rg->from, true);
>  			list_del(&rg->link);
>  			kfree(rg);
>  			continue;
> @@ -688,13 +710,13 @@ static long region_del(struct resv_map *resv, long f, long t)
>  
>  		if (f <= rg->from) {	/* Trim beginning of region */
>  			hugetlb_cgroup_uncharge_file_region(resv, rg,
> -							    t - rg->from);
> +							    t - rg->from, false);
>  
>  			del += t - rg->from;
>  			rg->from = t;
>  		} else {		/* Trim end of region */
>  			hugetlb_cgroup_uncharge_file_region(resv, rg,
> -							    rg->to - f);
> +							    rg->to - f, false);
>  
>  			del += rg->to - f;
>  			rg->to = f;
> @@ -5128,6 +5150,10 @@ bool hugetlb_reserve_pages(struct inode *inode,
>  			 */
>  			long rsv_adjust;
>  
> +			/*
> +			 * hugetlb_cgroup_uncharge_cgroup_rsvd() will put the
> +			 * reference to h_cg->css. See comment below for detail.
> +			 */
>  			hugetlb_cgroup_uncharge_cgroup_rsvd(
>  				hstate_index(h),
>  				(chg - add) * pages_per_huge_page(h), h_cg);
> @@ -5135,6 +5161,14 @@ bool hugetlb_reserve_pages(struct inode *inode,
>  			rsv_adjust = hugepage_subpool_put_pages(spool,
>  								chg - add);
>  			hugetlb_acct_memory(h, -rsv_adjust);
> +		} else if (h_cg) {
> +			/*
> +			 * The file_regions will hold their own reference to
> +			 * h_cg->css. So we should release the reference held
> +			 * via hugetlb_cgroup_charge_cgroup_rsvd() when we are
> +			 * done.
> +			 */
> +			hugetlb_cgroup_put_rsvd_cgroup(h_cg);
>  		}
>  	}
>  	return true;
> diff --git a/mm/hugetlb_cgroup.c b/mm/hugetlb_cgroup.c
> index f68b51fcda3d..8668ba87cfe4 100644
> --- a/mm/hugetlb_cgroup.c
> +++ b/mm/hugetlb_cgroup.c
> @@ -391,7 +391,8 @@ void hugetlb_cgroup_uncharge_counter(struct resv_map *resv, unsigned long start,
>  
>  void hugetlb_cgroup_uncharge_file_region(struct resv_map *resv,
>  					 struct file_region *rg,
> -					 unsigned long nr_pages)
> +					 unsigned long nr_pages,
> +					 bool region_del)
>  {
>  	if (hugetlb_cgroup_disabled() || !resv || !rg || !nr_pages)
>  		return;
> @@ -400,7 +401,13 @@ void hugetlb_cgroup_uncharge_file_region(struct resv_map *resv,
>  	    !resv->reservation_counter) {
>  		page_counter_uncharge(rg->reservation_counter,
>  				      nr_pages * resv->pages_per_hpage);
> -		css_put(rg->css);
> +		/*
> +		 * Only do css_put(rg->css) when we delete the entire region
> +		 * because one file_region must hold and only hold one rg->css

... must hold exactly one ...
Miaohe Lin March 13, 2021, 3:11 a.m. UTC | #2
On 2021/3/13 3:09, Mike Kravetz wrote:
> On 3/1/21 4:05 AM, Miaohe Lin wrote:
>> The current implementation of hugetlb_cgroup for shared mappings could have
>> different behavior. Consider the following two scenarios:
>>
>> 1.Assume initial css reference count of hugetlb_cgroup is 1:
>>   1.1 Call hugetlb_reserve_pages with from = 1, to = 2. So css reference
>> count is 2 associated with 1 file_region.
>>   1.2 Call hugetlb_reserve_pages with from = 2, to = 3. So css reference
>> count is 3 associated with 2 file_region.
>>   1.3 coalesce_file_region will coalesce these two file_regions into one.
>> So css reference count is 3 associated with 1 file_region now.
>>
>> 2.Assume initial css reference count of hugetlb_cgroup is 1 again:
>>   2.1 Call hugetlb_reserve_pages with from = 1, to = 3. So css reference
>> count is 2 associated with 1 file_region.
>>
>> Therefore, we might have one file_region while holding one or more css
>> reference counts. This inconsistency could lead to imbalanced css_get()
>> and css_put() pair. If we do css_put one by one (i.g. hole punch case),
>> scenario 2 would put one more css reference. If we do css_put all together
>> (i.g. truncate case), scenario 1 will leak one css reference.
>>
>> The imbalanced css_get() and css_put() pair would result in a non-zero
>> reference when we try to destroy the hugetlb cgroup. The hugetlb cgroup
>> directory is removed __but__ associated resource is not freed. This might
>> result in OOM or can not create a new hugetlb cgroup in a busy workload
>> ultimately.
>>
>> In order to fix this, we have to make sure that one file_region must hold
>> and only hold one css reference. So in coalesce_file_region case, we should
> 
> I think this would sound/read better if stated as:
> ... one file_region must hold exactly one css reference ...
> 
> This phrase is repeated in comments throughout the patch.
> 
>> release one css reference before coalescence. Also only put css reference
>> when the entire file_region is removed.
>>
>> The last thing to note is that the caller of region_add() will only hold
>> one reference to h_cg->css for the whole contiguous reservation region.
>> But this area might be scattered when there are already some file_regions
>> reside in it. As a result, many file_regions may share only one h_cg->css
>> reference. In order to ensure that one file_region must hold and only hold
>> one h_cg->css reference, we should do css_get() for each file_region and
>> release the reference held by caller when they are done.
> 
> Thanks for adding this to the commit message.
> 
>>
>> Fixes: 075a61d07a8e ("hugetlb_cgroup: add accounting for shared mappings")
>> Reported-by: kernel test robot <lkp@intel.com> (auto build test ERROR)
>> Signed-off-by: Miaohe Lin <linmiaohe@huawei.com>
>> Cc: stable@kernel.org
>> ---
>> v1->v2:
>> 	Fix auto build test ERROR when CGROUP_HUGETLB is disabled.
>> ---
>>  include/linux/hugetlb_cgroup.h | 15 ++++++++++--
>>  mm/hugetlb.c                   | 42 ++++++++++++++++++++++++++++++----
>>  mm/hugetlb_cgroup.c            | 11 +++++++--
>>  3 files changed, 60 insertions(+), 8 deletions(-)
> 
> Just a few minor nits below, all in comments.  It is not required, but
> would be nice to update these.  Code looks good.
> 

Many thanks for review! I will fix all this nits. Should I resend this patch or send another
one to fix this? Just let me know which is the easiest one for you.

Thanks again. :)

> Reviewed-by: Mike Kravetz <mike.kravetz@oracle.com>
> 
>>
>> diff --git a/include/linux/hugetlb_cgroup.h b/include/linux/hugetlb_cgroup.h
>> index 2ad6e92f124a..0bff345c4bc6 100644
>> --- a/include/linux/hugetlb_cgroup.h
>> +++ b/include/linux/hugetlb_cgroup.h
>> @@ -113,6 +113,11 @@ static inline bool hugetlb_cgroup_disabled(void)
>>  	return !cgroup_subsys_enabled(hugetlb_cgrp_subsys);
>>  }
>>  
>> +static inline void hugetlb_cgroup_put_rsvd_cgroup(struct hugetlb_cgroup *h_cg)
>> +{
>> +	css_put(&h_cg->css);
>> +}
>> +
>>  extern int hugetlb_cgroup_charge_cgroup(int idx, unsigned long nr_pages,
>>  					struct hugetlb_cgroup **ptr);
>>  extern int hugetlb_cgroup_charge_cgroup_rsvd(int idx, unsigned long nr_pages,
>> @@ -138,7 +143,8 @@ extern void hugetlb_cgroup_uncharge_counter(struct resv_map *resv,
>>  
>>  extern void hugetlb_cgroup_uncharge_file_region(struct resv_map *resv,
>>  						struct file_region *rg,
>> -						unsigned long nr_pages);
>> +						unsigned long nr_pages,
>> +						bool region_del);
>>  
>>  extern void hugetlb_cgroup_file_init(void) __init;
>>  extern void hugetlb_cgroup_migrate(struct page *oldhpage,
>> @@ -147,7 +153,8 @@ extern void hugetlb_cgroup_migrate(struct page *oldhpage,
>>  #else
>>  static inline void hugetlb_cgroup_uncharge_file_region(struct resv_map *resv,
>>  						       struct file_region *rg,
>> -						       unsigned long nr_pages)
>> +						       unsigned long nr_pages,
>> +						       bool region_del)
>>  {
>>  }
>>  
>> @@ -185,6 +192,10 @@ static inline bool hugetlb_cgroup_disabled(void)
>>  	return true;
>>  }
>>  
>> +static inline void hugetlb_cgroup_put_rsvd_cgroup(struct hugetlb_cgroup *h_cg)
>> +{
>> +}
>> +
>>  static inline int hugetlb_cgroup_charge_cgroup(int idx, unsigned long nr_pages,
>>  					       struct hugetlb_cgroup **ptr)
>>  {
>> diff --git a/mm/hugetlb.c b/mm/hugetlb.c
>> index 8fb42c6dd74b..87db91dff47f 100644
>> --- a/mm/hugetlb.c
>> +++ b/mm/hugetlb.c
>> @@ -280,6 +280,18 @@ static void record_hugetlb_cgroup_uncharge_info(struct hugetlb_cgroup *h_cg,
>>  		nrg->reservation_counter =
>>  			&h_cg->rsvd_hugepage[hstate_index(h)];
>>  		nrg->css = &h_cg->css;
>> +		/*
>> +		 * The caller (hugetlb_reserve_pages now) will only hold one
> 
> This can be called from other places such as alloc_huge_page.  Correct?
> If so, we should drop the mention of hugetlb_reserve_pages.
> 
>> +		 * h_cg->css reference for the whole contiguous reservation
>> +		 * region. But this area might be scattered when there are
>> +		 * already some file_regions reside in it. As a result, many
>> +		 * file_regions may share only one h_cg->css reference. In
>> +		 * order to ensure that one file_region must hold and only
>> +		 * hold one h_cg->css reference, we should do css_get for
> 
> ... must hold exactly one ...
> 
>> +		 * each file_region and leave the reference held by caller
>> +		 * untouched.
>> +		 */
>> +		css_get(&h_cg->css);
>>  		if (!resv->pages_per_hpage)
>>  			resv->pages_per_hpage = pages_per_huge_page(h);
>>  		/* pages_per_hpage should be the same for all entries in
>> @@ -293,6 +305,14 @@ static void record_hugetlb_cgroup_uncharge_info(struct hugetlb_cgroup *h_cg,
>>  #endif
>>  }
>>  
>> +static void put_uncharge_info(struct file_region *rg)
>> +{
>> +#ifdef CONFIG_CGROUP_HUGETLB
>> +	if (rg->css)
>> +		css_put(rg->css);
>> +#endif
>> +}
>> +
>>  static bool has_same_uncharge_info(struct file_region *rg,
>>  				   struct file_region *org)
>>  {
>> @@ -316,6 +336,7 @@ static void coalesce_file_region(struct resv_map *resv, struct file_region *rg)
>>  		prg->to = rg->to;
>>  
>>  		list_del(&rg->link);
>> +		put_uncharge_info(rg);
>>  		kfree(rg);
>>  
>>  		rg = prg;
>> @@ -327,6 +348,7 @@ static void coalesce_file_region(struct resv_map *resv, struct file_region *rg)
>>  		nrg->from = rg->from;
>>  
>>  		list_del(&rg->link);
>> +		put_uncharge_info(rg);
>>  		kfree(rg);
>>  	}
>>  }
>> @@ -659,7 +681,7 @@ static long region_del(struct resv_map *resv, long f, long t)
>>  
>>  			del += t - f;
>>  			hugetlb_cgroup_uncharge_file_region(
>> -				resv, rg, t - f);
>> +				resv, rg, t - f, false);
>>  
>>  			/* New entry for end of split region */
>>  			nrg->from = t;
>> @@ -680,7 +702,7 @@ static long region_del(struct resv_map *resv, long f, long t)
>>  		if (f <= rg->from && t >= rg->to) { /* Remove entire region */
>>  			del += rg->to - rg->from;
>>  			hugetlb_cgroup_uncharge_file_region(resv, rg,
>> -							    rg->to - rg->from);
>> +							    rg->to - rg->from, true);
>>  			list_del(&rg->link);
>>  			kfree(rg);
>>  			continue;
>> @@ -688,13 +710,13 @@ static long region_del(struct resv_map *resv, long f, long t)
>>  
>>  		if (f <= rg->from) {	/* Trim beginning of region */
>>  			hugetlb_cgroup_uncharge_file_region(resv, rg,
>> -							    t - rg->from);
>> +							    t - rg->from, false);
>>  
>>  			del += t - rg->from;
>>  			rg->from = t;
>>  		} else {		/* Trim end of region */
>>  			hugetlb_cgroup_uncharge_file_region(resv, rg,
>> -							    rg->to - f);
>> +							    rg->to - f, false);
>>  
>>  			del += rg->to - f;
>>  			rg->to = f;
>> @@ -5128,6 +5150,10 @@ bool hugetlb_reserve_pages(struct inode *inode,
>>  			 */
>>  			long rsv_adjust;
>>  
>> +			/*
>> +			 * hugetlb_cgroup_uncharge_cgroup_rsvd() will put the
>> +			 * reference to h_cg->css. See comment below for detail.
>> +			 */
>>  			hugetlb_cgroup_uncharge_cgroup_rsvd(
>>  				hstate_index(h),
>>  				(chg - add) * pages_per_huge_page(h), h_cg);
>> @@ -5135,6 +5161,14 @@ bool hugetlb_reserve_pages(struct inode *inode,
>>  			rsv_adjust = hugepage_subpool_put_pages(spool,
>>  								chg - add);
>>  			hugetlb_acct_memory(h, -rsv_adjust);
>> +		} else if (h_cg) {
>> +			/*
>> +			 * The file_regions will hold their own reference to
>> +			 * h_cg->css. So we should release the reference held
>> +			 * via hugetlb_cgroup_charge_cgroup_rsvd() when we are
>> +			 * done.
>> +			 */
>> +			hugetlb_cgroup_put_rsvd_cgroup(h_cg);
>>  		}
>>  	}
>>  	return true;
>> diff --git a/mm/hugetlb_cgroup.c b/mm/hugetlb_cgroup.c
>> index f68b51fcda3d..8668ba87cfe4 100644
>> --- a/mm/hugetlb_cgroup.c
>> +++ b/mm/hugetlb_cgroup.c
>> @@ -391,7 +391,8 @@ void hugetlb_cgroup_uncharge_counter(struct resv_map *resv, unsigned long start,
>>  
>>  void hugetlb_cgroup_uncharge_file_region(struct resv_map *resv,
>>  					 struct file_region *rg,
>> -					 unsigned long nr_pages)
>> +					 unsigned long nr_pages,
>> +					 bool region_del)
>>  {
>>  	if (hugetlb_cgroup_disabled() || !resv || !rg || !nr_pages)
>>  		return;
>> @@ -400,7 +401,13 @@ void hugetlb_cgroup_uncharge_file_region(struct resv_map *resv,
>>  	    !resv->reservation_counter) {
>>  		page_counter_uncharge(rg->reservation_counter,
>>  				      nr_pages * resv->pages_per_hpage);
>> -		css_put(rg->css);
>> +		/*
>> +		 * Only do css_put(rg->css) when we delete the entire region
>> +		 * because one file_region must hold and only hold one rg->css
> 
> ... must hold exactly one ...
>
Mike Kravetz March 15, 2021, 6:42 p.m. UTC | #3
On 3/12/21 7:11 PM, Miaohe Lin wrote:
> On 2021/3/13 3:09, Mike Kravetz wrote:
>> On 3/1/21 4:05 AM, Miaohe Lin wrote:
>>> The current implementation of hugetlb_cgroup for shared mappings could have
>>> different behavior. Consider the following two scenarios:
>>>
>>> 1.Assume initial css reference count of hugetlb_cgroup is 1:
>>>   1.1 Call hugetlb_reserve_pages with from = 1, to = 2. So css reference
>>> count is 2 associated with 1 file_region.
>>>   1.2 Call hugetlb_reserve_pages with from = 2, to = 3. So css reference
>>> count is 3 associated with 2 file_region.
>>>   1.3 coalesce_file_region will coalesce these two file_regions into one.
>>> So css reference count is 3 associated with 1 file_region now.
>>>
>>> 2.Assume initial css reference count of hugetlb_cgroup is 1 again:
>>>   2.1 Call hugetlb_reserve_pages with from = 1, to = 3. So css reference
>>> count is 2 associated with 1 file_region.
>>>
>>> Therefore, we might have one file_region while holding one or more css
>>> reference counts. This inconsistency could lead to imbalanced css_get()
>>> and css_put() pair. If we do css_put one by one (i.g. hole punch case),
>>> scenario 2 would put one more css reference. If we do css_put all together
>>> (i.g. truncate case), scenario 1 will leak one css reference.
>>>
>>> The imbalanced css_get() and css_put() pair would result in a non-zero
>>> reference when we try to destroy the hugetlb cgroup. The hugetlb cgroup
>>> directory is removed __but__ associated resource is not freed. This might
>>> result in OOM or can not create a new hugetlb cgroup in a busy workload
>>> ultimately.
>>>
>>> In order to fix this, we have to make sure that one file_region must hold
>>> and only hold one css reference. So in coalesce_file_region case, we should
>>
>> I think this would sound/read better if stated as:
>> ... one file_region must hold exactly one css reference ...
>>
>> This phrase is repeated in comments throughout the patch.
>>
>>> release one css reference before coalescence. Also only put css reference
>>> when the entire file_region is removed.
>>>
>>> The last thing to note is that the caller of region_add() will only hold
>>> one reference to h_cg->css for the whole contiguous reservation region.
>>> But this area might be scattered when there are already some file_regions
>>> reside in it. As a result, many file_regions may share only one h_cg->css
>>> reference. In order to ensure that one file_region must hold and only hold
>>> one h_cg->css reference, we should do css_get() for each file_region and
>>> release the reference held by caller when they are done.
>>
>> Thanks for adding this to the commit message.
>>
>>>
>>> Fixes: 075a61d07a8e ("hugetlb_cgroup: add accounting for shared mappings")
>>> Reported-by: kernel test robot <lkp@intel.com> (auto build test ERROR)
>>> Signed-off-by: Miaohe Lin <linmiaohe@huawei.com>
>>> Cc: stable@kernel.org
>>> ---
>>> v1->v2:
>>> 	Fix auto build test ERROR when CGROUP_HUGETLB is disabled.
>>> ---
>>>  include/linux/hugetlb_cgroup.h | 15 ++++++++++--
>>>  mm/hugetlb.c                   | 42 ++++++++++++++++++++++++++++++----
>>>  mm/hugetlb_cgroup.c            | 11 +++++++--
>>>  3 files changed, 60 insertions(+), 8 deletions(-)
>>
>> Just a few minor nits below, all in comments.  It is not required, but
>> would be nice to update these.  Code looks good.
>>
> 
> Many thanks for review! I will fix all this nits. Should I resend this patch or send another
> one to fix this? Just let me know which is the easiest one for you.
> 
> Thanks again. :)
> 

This is really Andrew's call as it goes through his tree.

I would suggest you just update the comments and send another verion.
In that way, Andrew can do whatever is easiest for him.
Miaohe Lin March 16, 2021, 1:47 a.m. UTC | #4
On 2021/3/16 2:42, Mike Kravetz wrote:
> On 3/12/21 7:11 PM, Miaohe Lin wrote:
>> On 2021/3/13 3:09, Mike Kravetz wrote:
>>> On 3/1/21 4:05 AM, Miaohe Lin wrote:
>>>> The current implementation of hugetlb_cgroup for shared mappings could have
>>>> different behavior. Consider the following two scenarios:
>>>>
>>>> 1.Assume initial css reference count of hugetlb_cgroup is 1:
>>>>   1.1 Call hugetlb_reserve_pages with from = 1, to = 2. So css reference
>>>> count is 2 associated with 1 file_region.
>>>>   1.2 Call hugetlb_reserve_pages with from = 2, to = 3. So css reference
>>>> count is 3 associated with 2 file_region.
>>>>   1.3 coalesce_file_region will coalesce these two file_regions into one.
>>>> So css reference count is 3 associated with 1 file_region now.
>>>>
>>>> 2.Assume initial css reference count of hugetlb_cgroup is 1 again:
>>>>   2.1 Call hugetlb_reserve_pages with from = 1, to = 3. So css reference
>>>> count is 2 associated with 1 file_region.
>>>>
>>>> Therefore, we might have one file_region while holding one or more css
>>>> reference counts. This inconsistency could lead to imbalanced css_get()
>>>> and css_put() pair. If we do css_put one by one (i.g. hole punch case),
>>>> scenario 2 would put one more css reference. If we do css_put all together
>>>> (i.g. truncate case), scenario 1 will leak one css reference.
>>>>
>>>> The imbalanced css_get() and css_put() pair would result in a non-zero
>>>> reference when we try to destroy the hugetlb cgroup. The hugetlb cgroup
>>>> directory is removed __but__ associated resource is not freed. This might
>>>> result in OOM or can not create a new hugetlb cgroup in a busy workload
>>>> ultimately.
>>>>
>>>> In order to fix this, we have to make sure that one file_region must hold
>>>> and only hold one css reference. So in coalesce_file_region case, we should
>>>
>>> I think this would sound/read better if stated as:
>>> ... one file_region must hold exactly one css reference ...
>>>
>>> This phrase is repeated in comments throughout the patch.
>>>
>>>> release one css reference before coalescence. Also only put css reference
>>>> when the entire file_region is removed.
>>>>
>>>> The last thing to note is that the caller of region_add() will only hold
>>>> one reference to h_cg->css for the whole contiguous reservation region.
>>>> But this area might be scattered when there are already some file_regions
>>>> reside in it. As a result, many file_regions may share only one h_cg->css
>>>> reference. In order to ensure that one file_region must hold and only hold
>>>> one h_cg->css reference, we should do css_get() for each file_region and
>>>> release the reference held by caller when they are done.
>>>
>>> Thanks for adding this to the commit message.
>>>
>>>>
>>>> Fixes: 075a61d07a8e ("hugetlb_cgroup: add accounting for shared mappings")
>>>> Reported-by: kernel test robot <lkp@intel.com> (auto build test ERROR)
>>>> Signed-off-by: Miaohe Lin <linmiaohe@huawei.com>
>>>> Cc: stable@kernel.org
>>>> ---
>>>> v1->v2:
>>>> 	Fix auto build test ERROR when CGROUP_HUGETLB is disabled.
>>>> ---
>>>>  include/linux/hugetlb_cgroup.h | 15 ++++++++++--
>>>>  mm/hugetlb.c                   | 42 ++++++++++++++++++++++++++++++----
>>>>  mm/hugetlb_cgroup.c            | 11 +++++++--
>>>>  3 files changed, 60 insertions(+), 8 deletions(-)
>>>
>>> Just a few minor nits below, all in comments.  It is not required, but
>>> would be nice to update these.  Code looks good.
>>>
>>
>> Many thanks for review! I will fix all this nits. Should I resend this patch or send another
>> one to fix this? Just let me know which is the easiest one for you.
>>
>> Thanks again. :)
>>
> 
> This is really Andrew's call as it goes through his tree.
> 

Sorry, I should have sought advice from Andrew explictly.

> I would suggest you just update the comments and send another verion.
> In that way, Andrew can do whatever is easiest for him.

Will send v3. Many thanks.

>

Patch
diff mbox series

diff --git a/include/linux/hugetlb_cgroup.h b/include/linux/hugetlb_cgroup.h
index 2ad6e92f124a..0bff345c4bc6 100644
--- a/include/linux/hugetlb_cgroup.h
+++ b/include/linux/hugetlb_cgroup.h
@@ -113,6 +113,11 @@  static inline bool hugetlb_cgroup_disabled(void)
 	return !cgroup_subsys_enabled(hugetlb_cgrp_subsys);
 }
 
+static inline void hugetlb_cgroup_put_rsvd_cgroup(struct hugetlb_cgroup *h_cg)
+{
+	css_put(&h_cg->css);
+}
+
 extern int hugetlb_cgroup_charge_cgroup(int idx, unsigned long nr_pages,
 					struct hugetlb_cgroup **ptr);
 extern int hugetlb_cgroup_charge_cgroup_rsvd(int idx, unsigned long nr_pages,
@@ -138,7 +143,8 @@  extern void hugetlb_cgroup_uncharge_counter(struct resv_map *resv,
 
 extern void hugetlb_cgroup_uncharge_file_region(struct resv_map *resv,
 						struct file_region *rg,
-						unsigned long nr_pages);
+						unsigned long nr_pages,
+						bool region_del);
 
 extern void hugetlb_cgroup_file_init(void) __init;
 extern void hugetlb_cgroup_migrate(struct page *oldhpage,
@@ -147,7 +153,8 @@  extern void hugetlb_cgroup_migrate(struct page *oldhpage,
 #else
 static inline void hugetlb_cgroup_uncharge_file_region(struct resv_map *resv,
 						       struct file_region *rg,
-						       unsigned long nr_pages)
+						       unsigned long nr_pages,
+						       bool region_del)
 {
 }
 
@@ -185,6 +192,10 @@  static inline bool hugetlb_cgroup_disabled(void)
 	return true;
 }
 
+static inline void hugetlb_cgroup_put_rsvd_cgroup(struct hugetlb_cgroup *h_cg)
+{
+}
+
 static inline int hugetlb_cgroup_charge_cgroup(int idx, unsigned long nr_pages,
 					       struct hugetlb_cgroup **ptr)
 {
diff --git a/mm/hugetlb.c b/mm/hugetlb.c
index 8fb42c6dd74b..87db91dff47f 100644
--- a/mm/hugetlb.c
+++ b/mm/hugetlb.c
@@ -280,6 +280,18 @@  static void record_hugetlb_cgroup_uncharge_info(struct hugetlb_cgroup *h_cg,
 		nrg->reservation_counter =
 			&h_cg->rsvd_hugepage[hstate_index(h)];
 		nrg->css = &h_cg->css;
+		/*
+		 * The caller (hugetlb_reserve_pages now) will only hold one
+		 * h_cg->css reference for the whole contiguous reservation
+		 * region. But this area might be scattered when there are
+		 * already some file_regions reside in it. As a result, many
+		 * file_regions may share only one h_cg->css reference. In
+		 * order to ensure that one file_region must hold and only
+		 * hold one h_cg->css reference, we should do css_get for
+		 * each file_region and leave the reference held by caller
+		 * untouched.
+		 */
+		css_get(&h_cg->css);
 		if (!resv->pages_per_hpage)
 			resv->pages_per_hpage = pages_per_huge_page(h);
 		/* pages_per_hpage should be the same for all entries in
@@ -293,6 +305,14 @@  static void record_hugetlb_cgroup_uncharge_info(struct hugetlb_cgroup *h_cg,
 #endif
 }
 
+static void put_uncharge_info(struct file_region *rg)
+{
+#ifdef CONFIG_CGROUP_HUGETLB
+	if (rg->css)
+		css_put(rg->css);
+#endif
+}
+
 static bool has_same_uncharge_info(struct file_region *rg,
 				   struct file_region *org)
 {
@@ -316,6 +336,7 @@  static void coalesce_file_region(struct resv_map *resv, struct file_region *rg)
 		prg->to = rg->to;
 
 		list_del(&rg->link);
+		put_uncharge_info(rg);
 		kfree(rg);
 
 		rg = prg;
@@ -327,6 +348,7 @@  static void coalesce_file_region(struct resv_map *resv, struct file_region *rg)
 		nrg->from = rg->from;
 
 		list_del(&rg->link);
+		put_uncharge_info(rg);
 		kfree(rg);
 	}
 }
@@ -659,7 +681,7 @@  static long region_del(struct resv_map *resv, long f, long t)
 
 			del += t - f;
 			hugetlb_cgroup_uncharge_file_region(
-				resv, rg, t - f);
+				resv, rg, t - f, false);
 
 			/* New entry for end of split region */
 			nrg->from = t;
@@ -680,7 +702,7 @@  static long region_del(struct resv_map *resv, long f, long t)
 		if (f <= rg->from && t >= rg->to) { /* Remove entire region */
 			del += rg->to - rg->from;
 			hugetlb_cgroup_uncharge_file_region(resv, rg,
-							    rg->to - rg->from);
+							    rg->to - rg->from, true);
 			list_del(&rg->link);
 			kfree(rg);
 			continue;
@@ -688,13 +710,13 @@  static long region_del(struct resv_map *resv, long f, long t)
 
 		if (f <= rg->from) {	/* Trim beginning of region */
 			hugetlb_cgroup_uncharge_file_region(resv, rg,
-							    t - rg->from);
+							    t - rg->from, false);
 
 			del += t - rg->from;
 			rg->from = t;
 		} else {		/* Trim end of region */
 			hugetlb_cgroup_uncharge_file_region(resv, rg,
-							    rg->to - f);
+							    rg->to - f, false);
 
 			del += rg->to - f;
 			rg->to = f;
@@ -5128,6 +5150,10 @@  bool hugetlb_reserve_pages(struct inode *inode,
 			 */
 			long rsv_adjust;
 
+			/*
+			 * hugetlb_cgroup_uncharge_cgroup_rsvd() will put the
+			 * reference to h_cg->css. See comment below for detail.
+			 */
 			hugetlb_cgroup_uncharge_cgroup_rsvd(
 				hstate_index(h),
 				(chg - add) * pages_per_huge_page(h), h_cg);
@@ -5135,6 +5161,14 @@  bool hugetlb_reserve_pages(struct inode *inode,
 			rsv_adjust = hugepage_subpool_put_pages(spool,
 								chg - add);
 			hugetlb_acct_memory(h, -rsv_adjust);
+		} else if (h_cg) {
+			/*
+			 * The file_regions will hold their own reference to
+			 * h_cg->css. So we should release the reference held
+			 * via hugetlb_cgroup_charge_cgroup_rsvd() when we are
+			 * done.
+			 */
+			hugetlb_cgroup_put_rsvd_cgroup(h_cg);
 		}
 	}
 	return true;
diff --git a/mm/hugetlb_cgroup.c b/mm/hugetlb_cgroup.c
index f68b51fcda3d..8668ba87cfe4 100644
--- a/mm/hugetlb_cgroup.c
+++ b/mm/hugetlb_cgroup.c
@@ -391,7 +391,8 @@  void hugetlb_cgroup_uncharge_counter(struct resv_map *resv, unsigned long start,
 
 void hugetlb_cgroup_uncharge_file_region(struct resv_map *resv,
 					 struct file_region *rg,
-					 unsigned long nr_pages)
+					 unsigned long nr_pages,
+					 bool region_del)
 {
 	if (hugetlb_cgroup_disabled() || !resv || !rg || !nr_pages)
 		return;
@@ -400,7 +401,13 @@  void hugetlb_cgroup_uncharge_file_region(struct resv_map *resv,
 	    !resv->reservation_counter) {
 		page_counter_uncharge(rg->reservation_counter,
 				      nr_pages * resv->pages_per_hpage);
-		css_put(rg->css);
+		/*
+		 * Only do css_put(rg->css) when we delete the entire region
+		 * because one file_region must hold and only hold one rg->css
+		 * reference.
+		 */
+		if (region_del)
+			css_put(rg->css);
 	}
 }