alloc_tag: prevent enabling memory profiling if it was shut down

Memory profiling can be shut down due to reasons like a failure during
initialization.  When this happens, the user should not be able to
re-enable it.  Current sysctrl interface does not handle this properly and
will allow re-enabling memory profiling.  Fix this by checking for this
condition during sysctrl write operation.

Link: https://lkml.kernel.org/r/20250915212756.3998938-3-surenb@google.com
Signed-off-by: Suren Baghdasaryan <surenb@google.com>
Acked-by: Shakeel Butt <shakeel.butt@linux.dev>
Acked-by: Usama Arif <usamaarif642@gmail.com>
Cc: David Wang <00107082@163.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Kent Overstreet <kent.overstreet@linux.dev>
Cc: Pasha Tatashin <pasha.tatashin@soleen.com>
Cc: Sourav Panda <souravpanda@google.com>
Cc: Vlastimil Babka <vbabka@suse.cz>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

diff --git a/lib/alloc_tag.c b/lib/alloc_tag.c
index 715315f5d9bafcab98cf3635ed6b25a7ac28baaf..f79217427d812a29de36d93829c2f729d119fed7 100644 (file)
--- a/lib/alloc_tag.c
+++ b/lib/alloc_tag.c
@@ -766,6 +766,20 @@ struct page_ext_operations page_alloc_tagging_ops = {
 EXPORT_SYMBOL(page_alloc_tagging_ops);
 
 #ifdef CONFIG_SYSCTL
+/*
+ * Not using proc_do_static_key() directly to prevent enabling profiling
+ * after it was shut down.
+ */
+static int proc_mem_profiling_handler(const struct ctl_table *table, int write,
+                                     void *buffer, size_t *lenp, loff_t *ppos)
+{
+       if (!mem_profiling_support && write)
+               return -EINVAL;
+
+       return proc_do_static_key(table, write, buffer, lenp, ppos);
+}
+
+
 static struct ctl_table memory_allocation_profiling_sysctls[] = {
        {
                .procname       = "mem_profiling",
@@ -775,7 +789,7 @@ static struct ctl_table memory_allocation_profiling_sysctls[] = {
 #else
                .mode           = 0644,
 #endif
-               .proc_handler   = proc_do_static_key,
+               .proc_handler   = proc_mem_profiling_handler,
        },
 };