memcg: sanitize __mem_cgroup_try_charge() call protocol

Some callsites pass a memcg directly, some callsites pass an mm that
then has to be translated to a memcg.  This makes for a terrible
function interface.

Just push the mm-to-memcg translation into the respective callsites and
always pass a memcg to mem_cgroup_try_charge().

[mhocko@suse.cz: add charge mm helper]
Signed-off-by: Johannes Weiner <hannes@cmpxchg.org>
Acked-by: Michal Hocko <mhocko@suse.cz>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 102 insertions, 105 deletions

diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 7480022d4655..038b037f8d67 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -2575,7 +2575,7 @@ static int memcg_cpu_hotplug_callback(struct notifier_block *nb,
 }
 
 
-/* See __mem_cgroup_try_charge() for details */
+/* See mem_cgroup_try_charge() for details */
 enum {
         CHARGE_OK,              /* success */
         CHARGE_RETRY,           /* need to retry but retry is not bad */
@@ -2648,45 +2648,34 @@ static int mem_cgroup_do_charge(struct mem_cgroup *memcg, gfp_t gfp_mask,
         return CHARGE_NOMEM;
 }
 
-/*
- * __mem_cgroup_try_charge() does
- * 1. detect memcg to be charged against from passed *mm and *ptr,
- * 2. update res_counter
- * 3. call memory reclaim if necessary.
- *
- * In some special case, if the task is fatal, fatal_signal_pending() or
- * has TIF_MEMDIE, this function returns -EINTR while writing root_mem_cgroup
- * to *ptr. There are two reasons for this. 1: fatal threads should quit as soon
- * as possible without any hazards. 2: all pages should have a valid
- * pc->mem_cgroup. If mm is NULL and the caller doesn't pass a valid memcg
- * pointer, that is treated as a charge to root_mem_cgroup.
- *
- * So __mem_cgroup_try_charge() will return
- *  0       ...  on success, filling *ptr with a valid memcg pointer.
- *  -ENOMEM ...  charge failure because of resource limits.
- *  -EINTR  ...  if thread is fatal. *ptr is filled with root_mem_cgroup.
+/**
+ * mem_cgroup_try_charge - try charging a memcg
+ * @memcg: memcg to charge
+ * @nr_pages: number of pages to charge
+ * @oom: trigger OOM if reclaim fails
  *
- * Unlike the exported interface, an "oom" parameter is added. if oom==true,
- * the oom-killer can be invoked.
+ * Returns 0 if @memcg was charged successfully, -EINTR if the charge
+ * was bypassed to root_mem_cgroup, and -ENOMEM if the charge failed.
  */
-static int __mem_cgroup_try_charge(struct mm_struct *mm,
-                                   gfp_t gfp_mask,
-                                   unsigned int nr_pages,
-                                   struct mem_cgroup **ptr,
-                                   bool oom)
+static int mem_cgroup_try_charge(struct mem_cgroup *memcg,
+                                 gfp_t gfp_mask,
+                                 unsigned int nr_pages,
+                                 bool oom)
 {
         unsigned int batch = max(CHARGE_BATCH, nr_pages);
         int nr_oom_retries = MEM_CGROUP_RECLAIM_RETRIES;
-        struct mem_cgroup *memcg = NULL;
         int ret;
 
+        if (mem_cgroup_is_root(memcg))
+                goto done;
         /*
-         * Unlike gloval-vm's OOM-kill, we're not in memory shortage
-         * in system level. So, allow to go ahead dying process in addition to
-         * MEMDIE process.
+         * Unlike in global OOM situations, memcg is not in a physical
+         * memory shortage.  Allow dying and OOM-killed tasks to
+         * bypass the last charges so that they can exit quickly and
+         * free their memory.
          */
-        if (unlikely(test_thread_flag(TIF_MEMDIE)
-                     || fatal_signal_pending(current)))
+        if (unlikely(test_thread_flag(TIF_MEMDIE) ||
+                     fatal_signal_pending(current)))
                 goto bypass;
 
         if (unlikely(task_in_memcg_oom(current)))
@@ -2695,14 +2684,6 @@ static int __mem_cgroup_try_charge(struct mm_struct *mm,
         if (gfp_mask & __GFP_NOFAIL)
                 oom = false;
 again:
-        if (*ptr) { /* css should be a valid one */
-                memcg = *ptr;
-                css_get(&memcg->css);
-        } else {
-                memcg = get_mem_cgroup_from_mm(mm);
-        }
-        if (mem_cgroup_is_root(memcg))
-                goto done;
         if (consume_stock(memcg, nr_pages))
                 goto done;
 
@@ -2710,10 +2691,8 @@ again:
                 bool invoke_oom = oom && !nr_oom_retries;
 
                 /* If killed, bypass charge */
-                if (fatal_signal_pending(current)) {
-                        css_put(&memcg->css);
+                if (fatal_signal_pending(current))
                         goto bypass;
-                }
 
                 ret = mem_cgroup_do_charge(memcg, gfp_mask, batch,
                                            nr_pages, invoke_oom);
@@ -2722,17 +2701,12 @@ again:
                         break;
                 case CHARGE_RETRY: /* not in OOM situation but retry */
                         batch = nr_pages;
-                        css_put(&memcg->css);
-                        memcg = NULL;
                         goto again;
                 case CHARGE_WOULDBLOCK: /* !__GFP_WAIT */
-                        css_put(&memcg->css);
                         goto nomem;
                 case CHARGE_NOMEM: /* OOM routine works */
-                        if (!oom || invoke_oom) {
-                                css_put(&memcg->css);
+                        if (!oom || invoke_oom)
                                 goto nomem;
-                        }
                         nr_oom_retries--;
                         break;
                 }
@@ -2741,19 +2715,43 @@ again:
         if (batch > nr_pages)
                 refill_stock(memcg, batch - nr_pages);
 done:
-        css_put(&memcg->css);
-        *ptr = memcg;
         return 0;
 nomem:
-        if (!(gfp_mask & __GFP_NOFAIL)) {
-                *ptr = NULL;
+        if (!(gfp_mask & __GFP_NOFAIL))
                 return -ENOMEM;
-        }
 bypass:
-        *ptr = root_mem_cgroup;
         return -EINTR;
 }
 
+/**
+ * mem_cgroup_try_charge_mm - try charging a mm
+ * @mm: mm_struct to charge
+ * @nr_pages: number of pages to charge
+ * @oom: trigger OOM if reclaim fails
+ *
+ * Returns the charged mem_cgroup associated with the given mm_struct or
+ * NULL the charge failed.
+ */
+static struct mem_cgroup *mem_cgroup_try_charge_mm(struct mm_struct *mm,
+                                 gfp_t gfp_mask,
+                                 unsigned int nr_pages,
+                                 bool oom)
+
+{
+        struct mem_cgroup *memcg;
+        int ret;
+
+        memcg = get_mem_cgroup_from_mm(mm);
+        ret = mem_cgroup_try_charge(memcg, gfp_mask, nr_pages, oom);
+        css_put(&memcg->css);
+        if (ret == -EINTR)
+                memcg = root_mem_cgroup;
+        else if (ret)
+                memcg = NULL;
+
+        return memcg;
+}
+
 /*
  * Somemtimes we have to undo a charge we got by try_charge().
  * This function is for that and do uncharge, put css's refcnt.
@@ -2949,20 +2947,17 @@ static int mem_cgroup_slabinfo_read(struct seq_file *m, void *v)
 static int memcg_charge_kmem(struct mem_cgroup *memcg, gfp_t gfp, u64 size)
 {
         struct res_counter *fail_res;
-        struct mem_cgroup *_memcg;
         int ret = 0;
 
         ret = res_counter_charge(&memcg->kmem, size, &fail_res);
         if (ret)
                 return ret;
 
-        _memcg = memcg;
-        ret = __mem_cgroup_try_charge(NULL, gfp, size >> PAGE_SHIFT,
-                                      &_memcg, oom_gfp_allowed(gfp));
-
+        ret = mem_cgroup_try_charge(memcg, gfp, size >> PAGE_SHIFT,
+                                    oom_gfp_allowed(gfp));
         if (ret == -EINTR)  {
                 /*
-                 * __mem_cgroup_try_charge() chosed to bypass to root due to
+                 * mem_cgroup_try_charge() chosed to bypass to root due to
                  * OOM kill or fatal signal.  Since our only options are to
                  * either fail the allocation or charge it to this cgroup, do
                  * it as a temporary condition. But we can't fail. From a
@@ -2972,7 +2967,7 @@ static int memcg_charge_kmem(struct mem_cgroup *memcg, gfp_t gfp, u64 size)
                  *
                  * This condition will only trigger if the task entered
                  * memcg_charge_kmem in a sane state, but was OOM-killed during
-                 * __mem_cgroup_try_charge() above. Tasks that were already
+                 * mem_cgroup_try_charge() above. Tasks that were already
                  * dying when the allocation triggers should have been already
                  * directed to the root cgroup in memcontrol.h
                  */
@@ -3826,10 +3821,9 @@ out:
 int mem_cgroup_newpage_charge(struct page *page,
                               struct mm_struct *mm, gfp_t gfp_mask)
 {
-        struct mem_cgroup *memcg = NULL;
         unsigned int nr_pages = 1;
+        struct mem_cgroup *memcg;
         bool oom = true;
-        int ret;
 
         if (mem_cgroup_disabled())
                 return 0;
@@ -3848,9 +3842,9 @@ int mem_cgroup_newpage_charge(struct page *page,
                 oom = false;
         }
 
-        ret = __mem_cgroup_try_charge(mm, gfp_mask, nr_pages, &memcg, oom);
-        if (ret == -ENOMEM)
-                return ret;
+        memcg = mem_cgroup_try_charge_mm(mm, gfp_mask, nr_pages, oom);
+        if (!memcg)
+                return -ENOMEM;
         __mem_cgroup_commit_charge(memcg, page, nr_pages,
                                    MEM_CGROUP_CHARGE_TYPE_ANON, false);
         return 0;
@@ -3867,7 +3861,7 @@ static int __mem_cgroup_try_charge_swapin(struct mm_struct *mm,
                                           gfp_t mask,
                                           struct mem_cgroup **memcgp)
 {
-        struct mem_cgroup *memcg;
+        struct mem_cgroup *memcg = NULL;
         struct page_cgroup *pc;
         int ret;
 
@@ -3880,31 +3874,29 @@ static int __mem_cgroup_try_charge_swapin(struct mm_struct *mm,
          * in turn serializes uncharging.
          */
         if (PageCgroupUsed(pc))
-                return 0;
-        if (!do_swap_account)
-                goto charge_cur_mm;
-        memcg = try_get_mem_cgroup_from_page(page);
+                goto out;
+        if (do_swap_account)
+                memcg = try_get_mem_cgroup_from_page(page);
         if (!memcg)
-                goto charge_cur_mm;
-        *memcgp = memcg;
-        ret = __mem_cgroup_try_charge(NULL, mask, 1, memcgp, true);
+                memcg = get_mem_cgroup_from_mm(mm);
+        ret = mem_cgroup_try_charge(memcg, mask, 1, true);
         css_put(&memcg->css);
         if (ret == -EINTR)
-                ret = 0;
-        return ret;
-charge_cur_mm:
-        ret = __mem_cgroup_try_charge(mm, mask, 1, memcgp, true);
-        if (ret == -EINTR)
-                ret = 0;
-        return ret;
+                memcg = root_mem_cgroup;
+        else if (ret)
+                return ret;
+out:
+        *memcgp = memcg;
+        return 0;
 }
 
 int mem_cgroup_try_charge_swapin(struct mm_struct *mm, struct page *page,
                                  gfp_t gfp_mask, struct mem_cgroup **memcgp)
 {
-        *memcgp = NULL;
-        if (mem_cgroup_disabled())
+        if (mem_cgroup_disabled()) {
+                *memcgp = NULL;
                 return 0;
+        }
         /*
          * A racing thread's fault, or swapoff, may have already
          * updated the pte, and even removed page from swap cache: in
@@ -3912,12 +3904,13 @@ int mem_cgroup_try_charge_swapin(struct mm_struct *mm, struct page *page,
          * there's also a KSM case which does need to charge the page.
          */
         if (!PageSwapCache(page)) {
-                int ret;
+                struct mem_cgroup *memcg;
 
-                ret = __mem_cgroup_try_charge(mm, gfp_mask, 1, memcgp, true);
-                if (ret == -EINTR)
-                        ret = 0;
-                return ret;
+                memcg = mem_cgroup_try_charge_mm(mm, gfp_mask, 1, true);
+                if (!memcg)
+                        return -ENOMEM;
+                *memcgp = memcg;
+                return 0;
         }
         return __mem_cgroup_try_charge_swapin(mm, page, gfp_mask, memcgp);
 }
@@ -3964,8 +3957,8 @@ void mem_cgroup_commit_charge_swapin(struct page *page,
 int mem_cgroup_cache_charge(struct page *page, struct mm_struct *mm,
                                 gfp_t gfp_mask)
 {
-        struct mem_cgroup *memcg = NULL;
         enum charge_type type = MEM_CGROUP_CHARGE_TYPE_CACHE;
+        struct mem_cgroup *memcg;
         int ret;
 
         if (mem_cgroup_disabled())
@@ -3973,23 +3966,28 @@ int mem_cgroup_cache_charge(struct page *page, struct mm_struct *mm,
         if (PageCompound(page))
                 return 0;
 
-        if (!PageSwapCache(page)) {
-                /*
-                 * Page cache insertions can happen without an actual
-                 * task context, e.g. during disk probing on boot.
-                 */
-                if (!mm)
-                        memcg = root_mem_cgroup;
-                ret = __mem_cgroup_try_charge(mm, gfp_mask, 1, &memcg, true);
-                if (ret != -ENOMEM)
-                        __mem_cgroup_commit_charge(memcg, page, 1, type, false);
-        } else { /* page is swapcache/shmem */
+        if (PageSwapCache(page)) { /* shmem */
                 ret = __mem_cgroup_try_charge_swapin(mm, page,
                                                      gfp_mask, &memcg);
-                if (!ret)
-                        __mem_cgroup_commit_charge_swapin(page, memcg, type);
+                if (ret)
+                        return ret;
+                __mem_cgroup_commit_charge_swapin(page, memcg, type);
+                return 0;
         }
-        return ret;
+
+        /*
+         * Page cache insertions can happen without an actual mm
+         * context, e.g. during disk probing on boot.
+         */
+        if (unlikely(!mm))
+                memcg = root_mem_cgroup;
+        else {
+                memcg = mem_cgroup_try_charge_mm(mm, gfp_mask, 1, true);
+                if (!memcg)
+                        return -ENOMEM;
+        }
+        __mem_cgroup_commit_charge(memcg, page, 1, type, false);
+        return 0;
 }
 
 static void mem_cgroup_do_uncharge(struct mem_cgroup *memcg,
@@ -6601,8 +6599,7 @@ one_by_one:
                         batch_count = PRECHARGE_COUNT_AT_ONCE;
                         cond_resched();
                 }
-                ret = __mem_cgroup_try_charge(NULL,
-                                        GFP_KERNEL, 1, &memcg, false);
+                ret = mem_cgroup_try_charge(memcg, GFP_KERNEL, 1, false);
                 if (ret)
                         /* mem_cgroup_clear_mc() will do uncharge later */
                         return ret;