[FIX] proc: rewrite stable_page_flags()

[Matthew Wilcox <willy@infradead.org>]

On Wed, Apr 03, 2024 at 12:01:35PM +0300, Dan Carpenter wrote:
> Hello Matthew Wilcox (Oracle),
> 
> Commit ea1be2228bb6 ("proc: rewrite stable_page_flags()") from Mar
> 26, 2024 (linux-next), leads to the following Smatch static checker
> warning:
> 
> fs/proc/page.c:156 stable_page_flags() warn: bit shifter 'PG_lru' used for logical '&'
> fs/proc/page.c:207 stable_page_flags() warn: bit shifter 'KPF_HUGE' used for logical '&'

Thanks.  I thought I sent this out on Tuesday, but it doesn't seem to
have left my machine.  Andrew, can you add this -fix patch?

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