Re: [PATCH 7/9] mm: Free up PG_slab

[Matthew Wilcox]

On Sun, Mar 31, 2024 at 11:11:10PM +0800, kernel test robot wrote:
> kernel test robot noticed "UBSAN:shift-out-of-bounds_in_fs/proc/page.c" on:
> 
> commit: 30e5296811312a13938b83956a55839ac1e3aa40 ("[PATCH 7/9] mm: Free up PG_slab")

Quite right.  Spotted another one while I was at it.  Not able to test
right now, but this should do the trick:

diff --git a/fs/proc/page.c b/fs/proc/page.c
index 5bc82828c6aa..55b01535eb22 100644
--- a/fs/proc/page.c
+++ b/fs/proc/page.c
@@ -175,6 +175,8 @@ u64 stable_page_flags(const struct page *page)
 		u |= 1 << KPF_OFFLINE;
 	if (PageTable(page))
 		u |= 1 << KPF_PGTABLE;
+	if (folio_test_slab(folio))
+		u |= 1 << KPF_SLAB;
 
 #if defined(CONFIG_PAGE_IDLE_FLAG) && defined(CONFIG_64BIT)
 	u |= kpf_copy_bit(k, KPF_IDLE,          PG_idle);
@@ -184,7 +186,6 @@ u64 stable_page_flags(const struct page *page)
 #endif
 
 	u |= kpf_copy_bit(k, KPF_LOCKED,	PG_locked);
-	u |= kpf_copy_bit(k, KPF_SLAB,		PG_slab);
 	u |= kpf_copy_bit(k, KPF_ERROR,		PG_error);
 	u |= kpf_copy_bit(k, KPF_DIRTY,		PG_dirty);
 	u |= kpf_copy_bit(k, KPF_UPTODATE,	PG_uptodate);
diff --git a/tools/cgroup/memcg_slabinfo.py b/tools/cgroup/memcg_slabinfo.py
index 1d3a90d93fe2..270c28a0d098 100644
--- a/tools/cgroup/memcg_slabinfo.py
+++ b/tools/cgroup/memcg_slabinfo.py
@@ -146,12 +146,11 @@ def detect_kernel_config():
 
 
 def for_each_slab(prog):
-    PGSlab = 1 << prog.constant('PG_slab')
-    PGHead = 1 << prog.constant('PG_head')
+    PGSlab = ~prog.constant('PG_slab')
 
     for page in for_each_page(prog):
         try:
-            if page.flags.value_() & PGSlab:
+            if page.page_type.value_() == PGSlab:
                 yield cast('struct slab *', page)
         except FaultError:
             pass