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authorMiaohe Lin <linmiaohe@huawei.com>2021-03-24 21:37:17 -0700
committerLinus Torvalds <torvalds@linux-foundation.org>2021-03-25 09:22:55 -0700
commitd85aecf2844ff02a0e5f077252b2461d4f10c9f0 (patch)
tree6e758c83fbe1cb297b0c156717714873b49e4dde /mm
parent7acac4b3196caee5e21fb5ea53f8bc124e6a16fc (diff)
downloadlinux-d85aecf2844ff02a0e5f077252b2461d4f10c9f0.tar.bz2
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 exactly 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 exactly one css reference, we should do css_get() for each file_region and release the reference held by caller when they are done. [linmiaohe@huawei.com: fix imbalanced css_get and css_put pair for shared mappings] Link: https://lkml.kernel.org/r/20210316023002.53921-1-linmiaohe@huawei.com 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> Reviewed-by: Mike Kravetz <mike.kravetz@oracle.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: <stable@vger.kernel.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'mm')
-rw-r--r--mm/hugetlb.c41
-rw-r--r--mm/hugetlb_cgroup.c10
2 files changed, 45 insertions, 6 deletions
diff --git a/mm/hugetlb.c b/mm/hugetlb.c
index 5b1ab1f427c5..a86a58ef132d 100644
--- a/mm/hugetlb.c
+++ b/mm/hugetlb.c
@@ -280,6 +280,17 @@ 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 will hold exactly 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 css
+ * reference. In order to ensure that one file_region must hold
+ * exactly 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 +304,14 @@ 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 +335,7 @@ 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 +347,7 @@ 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);
}
}
@@ -662,7 +683,7 @@ 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;
@@ -683,7 +704,7 @@ 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;
@@ -691,13 +712,13 @@ 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;
@@ -5187,6 +5208,10 @@ 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);
@@ -5194,6 +5219,14 @@ 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..603a131e262d 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 +401,12 @@ 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 exactly one css reference.
+ */
+ if (region_del)
+ css_put(rg->css);
}
}