hugetlb_cgroup: fix imbalanced css_get and css_put pair for shared mappings
commit d85aecf2844ff02a0e5f077252b2461d4f10c9f0 upstream.
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>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
diff --git a/mm/hugetlb.c b/mm/hugetlb.c
index 94c6b3d..573f1a0 100644
--- a/mm/hugetlb.c
+++ b/mm/hugetlb.c
@@ -285,6 +285,17 @@ 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
@@ -298,6 +309,14 @@ 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)
{
@@ -321,6 +340,7 @@ 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;
@@ -332,6 +352,7 @@ 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);
}
}
@@ -664,7 +685,7 @@ 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;
@@ -685,7 +706,7 @@ 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;
@@ -693,13 +714,13 @@ 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;
@@ -5189,6 +5210,10 @@ int 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);
@@ -5196,6 +5221,14 @@ int 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 0;