livepatch: Convert stack entries array to percpu

The entries array in klp_check_stack() is static local because it's too
big to be reasonably allocated on the stack.  Serialized access is
enforced by the klp_mutex.

In preparation for calling klp_check_stack() without the mutex (from
cond_resched), convert it to a percpu variable.

Signed-off-by: Josh Poimboeuf <jpoimboe@kernel.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lkml.kernel.org/r/20230313233346.kayh4t2lpicjkpsv@treble

diff --git a/kernel/livepatch/transition.c b/kernel/livepatch/transition.c
index f1b25ec581e0d9a0783bf5f4a1764b2aa0b50df4..135fc73e2e5db06589cbdd462df4e46e31d7c1ba 100644 (file)
--- a/kernel/livepatch/transition.c
+++ b/kernel/livepatch/transition.c
@@ -14,6 +14,8 @@
 #include "transition.h"
 
 #define MAX_STACK_ENTRIES  100
+DEFINE_PER_CPU(unsigned long[MAX_STACK_ENTRIES], klp_stack_entries);
+
 #define STACK_ERR_BUF_SIZE 128
 
 #define SIGNALS_TIMEOUT 15
@@ -240,12 +242,15 @@ static int klp_check_stack_func(struct klp_func *func, unsigned long *entries,
  */
 static int klp_check_stack(struct task_struct *task, const char **oldname)
 {
-       static unsigned long entries[MAX_STACK_ENTRIES];
+       unsigned long *entries = this_cpu_ptr(klp_stack_entries);
        struct klp_object *obj;
        struct klp_func *func;
        int ret, nr_entries;
 
-       ret = stack_trace_save_tsk_reliable(task, entries, ARRAY_SIZE(entries));
+       /* Protect 'klp_stack_entries' */
+       lockdep_assert_preemption_disabled();
+
+       ret = stack_trace_save_tsk_reliable(task, entries, MAX_STACK_ENTRIES);
        if (ret < 0)
                return -EINVAL;
        nr_entries = ret;