Re: [PATCH] mm: kfence: fix PG_slab and memcg_data clearing

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On 2023/3/21 12:14, Peng Zhang wrote:

在 2023/3/20 11:00, Muchun Song 写道:
It does not reset PG_slab and memcg_data when KFENCE fails to initialize
kfence pool at runtime. It is reporting a "Bad page state" message when
kfence pool is freed to buddy. The checking of whether it is a compound
head page seems unnecessary sicne we already guarantee this when allocating
kfence pool, removing the check to simplify the code.

Fixes: 0ce20dd84089 ("mm: add Kernel Electric-Fence infrastructure")
Fixes: 8f0b36497303 ("mm: kfence: fix objcgs vector allocation")
Signed-off-by: Muchun Song <songmuchun@xxxxxxxxxxxxx>
---
  mm/kfence/core.c | 30 +++++++++++++++---------------
  1 file changed, 15 insertions(+), 15 deletions(-)

diff --git a/mm/kfence/core.c b/mm/kfence/core.c
index 79c94ee55f97..d66092dd187c 100644
--- a/mm/kfence/core.c
+++ b/mm/kfence/core.c
@@ -561,10 +561,6 @@ static unsigned long kfence_init_pool(void)
          if (!i || (i % 2))
              continue;
  -        /* Verify we do not have a compound head page. */
-        if (WARN_ON(compound_head(&pages[i]) != &pages[i]))
-            return addr;
-
          __folio_set_slab(slab_folio(slab));
  #ifdef CONFIG_MEMCG
          slab->memcg_data = (unsigned long)&kfence_metadata[i / 2 - 1].objcg |
@@ -597,12 +593,26 @@ static unsigned long kfence_init_pool(void)
            /* Protect the right redzone. */
          if (unlikely(!kfence_protect(addr + PAGE_SIZE)))
-            return addr;
+            goto reset_slab;
            addr += 2 * PAGE_SIZE;
      }
        return 0;
+
+reset_slab:
+    for (i = 0; i < KFENCE_POOL_SIZE / PAGE_SIZE; i++) {
+        struct slab *slab = page_slab(&pages[i]);
+
+        if (!i || (i % 2))
+            continue;
+#ifdef CONFIG_MEMCG
+        slab->memcg_data = 0;
+#endif
+        __folio_clear_slab(slab_folio(slab));
+    }
Can this loop be simplified to this?

    for (i = 2; i < KFENCE_POOL_SIZE / PAGE_SIZE; i+=2) {
        struct slab *slab = page_slab(&pages[i]);
#ifdef CONFIG_MEMCG
        slab->memcg_data = 0;
#endif
        __folio_clear_slab(slab_folio(slab));
    }


It's a good simplification. The loop setting Pg_slab before this
also can be simplified in the same way. However, I choose a
consistent way to fix this bug. I'd like to send a separate
simplification patch to simplify both two loops instead of
in a bugfix patch.

Thanks.




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