Eric Lee / linux-smarc-t335x-v3.2

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Commit 7bcc1bb1232de6efc0b85e0c7fe38e90b2436318

Authored by Daisuke Nishimura
Committed by Linus Torvalds
1 parent baef99a08a
Exists in master and in 4 other branches v3.2_AM335xPSP_04.06.00.11, v3.2_NEWT335xPSP_04.06.00.11, v3.2_SBC_SMARTMEN, v3.2_SMARCT335xPSP_04.06.00.11

memcg: get/put parents at create/free 

The lifetime of struct cgroup and struct mem_cgroup is different and
mem_cgroup has its own reference count for handling references from
swap_cgroup.

This causes strange problem that the parent mem_cgroup dies while child
mem_cgroup alive, and this problem causes a bug in case of
use_hierarchy==1 because res_counter_uncharge climbs up the tree.

This patch is for avoiding it by getting the parent at create, and putting
it at freeing.

Signed-off-by: Daisuke Nishimura <nishimura@mxp.nes.nec.co.jp>
Reviewed-by; KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Balbir Singh <balbir@linux.vnet.ibm.com>
Cc: Pavel Emelyanov <xemul@openvz.org>
Cc: Li Zefan <lizf@cn.fujitsu.com>
Cc: Paul Menage <menage@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

Showing 1 changed file with 22 additions and 1 deletions Side-by-side Diff

... ... @@ -202,6 +202,7 @@
202 202  
203 203 static void mem_cgroup_get(struct mem_cgroup *mem);
204 204 static void mem_cgroup_put(struct mem_cgroup *mem);
  205 +static struct mem_cgroup *parent_mem_cgroup(struct mem_cgroup *mem);
205 206  
206 207 static void mem_cgroup_charge_statistics(struct mem_cgroup *mem,
207 208 struct page_cgroup *pc,
208 209  
209 210  
... ... @@ -2193,10 +2194,23 @@
2193 2194  
2194 2195 static void mem_cgroup_put(struct mem_cgroup *mem)
2195 2196 {
2196   - if (atomic_dec_and_test(&mem->refcnt))
  2197 + if (atomic_dec_and_test(&mem->refcnt)) {
  2198 + struct mem_cgroup *parent = parent_mem_cgroup(mem);
2197 2199 __mem_cgroup_free(mem);
  2200 + if (parent)
  2201 + mem_cgroup_put(parent);
  2202 + }
2198 2203 }
2199 2204  
  2205 +/*
  2206 + * Returns the parent mem_cgroup in memcgroup hierarchy with hierarchy enabled.
  2207 + */
  2208 +static struct mem_cgroup *parent_mem_cgroup(struct mem_cgroup *mem)
  2209 +{
  2210 + if (!mem->res.parent)
  2211 + return NULL;
  2212 + return mem_cgroup_from_res_counter(mem->res.parent, res);
  2213 +}
2200 2214  
2201 2215 #ifdef CONFIG_CGROUP_MEM_RES_CTLR_SWAP
2202 2216 static void __init enable_swap_cgroup(void)
... ... @@ -2235,6 +2249,13 @@
2235 2249 if (parent && parent->use_hierarchy) {
2236 2250 res_counter_init(&mem->res, &parent->res);
2237 2251 res_counter_init(&mem->memsw, &parent->memsw);
  2252 + /*
  2253 + * We increment refcnt of the parent to ensure that we can
  2254 + * safely access it on res_counter_charge/uncharge.
  2255 + * This refcnt will be decremented when freeing this
  2256 + * mem_cgroup(see mem_cgroup_put).
  2257 + */
  2258 + mem_cgroup_get(parent);
2238 2259 } else {
2239 2260 res_counter_init(&mem->res, NULL);
2240 2261 res_counter_init(&mem->memsw, NULL);