The patch titled Subject: hugetlb_cgroup: fix imbalanced css_get and css_put pair for shared mappings has been added to the -mm tree. Its filename is hugetlb_cgroup-fix-imbalanced-css_get-and-css_put-pair-for-shared-mappings.patch
This patch should soon appear at https://ozlabs.org/~akpm/mmots/broken-out/hugetlb_cgroup-fix-imbalanced-css_... and later at https://ozlabs.org/~akpm/mmotm/broken-out/hugetlb_cgroup-fix-imbalanced-css_...
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------------------------------------------------------ From: Miaohe Lin linmiaohe@huawei.com Subject: hugetlb_cgroup: fix imbalanced css_get and css_put pair for shared mappings
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.
Link: https://lkml.kernel.org/r/20210301120540.37076-1-linmiaohe@huawei.com 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: Aneesh Kumar K.V aneesh.kumar@linux.vnet.ibm.com Cc: Wanpeng Li liwp.linux@gmail.com Cc: Mina Almasry almasrymina@google.com Cc: Mike Kravetz mike.kravetz@oracle.com Cc: stable@vger.kernel.org Signed-off-by: Andrew Morton akpm@linux-foundation.org ---
include/linux/hugetlb_cgroup.h | 15 +++++++++-- mm/hugetlb.c | 42 ++++++++++++++++++++++++++++--- mm/hugetlb_cgroup.c | 11 ++++++-- 3 files changed, 60 insertions(+), 8 deletions(-)
--- a/include/linux/hugetlb_cgroup.h~hugetlb_cgroup-fix-imbalanced-css_get-and-css_put-pair-for-shared-mappings +++ a/include/linux/hugetlb_cgroup.h @@ -113,6 +113,11 @@ static inline bool hugetlb_cgroup_disabl 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_coun
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(struc #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_disabl 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) { --- a/mm/hugetlb.c~hugetlb_cgroup-fix-imbalanced-css_get-and-css_put-pair-for-shared-mappings +++ a/mm/hugetlb.c @@ -280,6 +280,18 @@ static void record_hugetlb_cgroup_unchar 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_unchar #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 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 nrg->from = rg->from;
list_del(&rg->link); + put_uncharge_info(rg); kfree(rg); } } @@ -659,7 +681,7 @@ retry:
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 @@ retry: 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 @@ retry:
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 */ 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 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; --- a/mm/hugetlb_cgroup.c~hugetlb_cgroup-fix-imbalanced-css_get-and-css_put-pair-for-shared-mappings +++ a/mm/hugetlb_cgroup.c @@ -391,7 +391,8 @@ void hugetlb_cgroup_uncharge_counter(str
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 !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); } }
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Patches currently in -mm which might be from linmiaohe@huawei.com are
hugetlb_cgroup-fix-imbalanced-css_get-and-css_put-pair-for-shared-mappings.patch