[tip: sched/core] livepatch: Convert stack entries array to percpu

[tip-bot2 for Josh Poimboeuf]

The following commit has been merged into the sched/core branch of tip:

Commit-ID:     e92606fa172f63a26054885b9715be86c643229d
Gitweb:        https://git.kernel.org/tip/e92606fa172f63a26054885b9715be86c643229d
Author:        Josh Poimboeuf <jpoimboe@xxxxxxxxxx>
AuthorDate:    Mon, 13 Mar 2023 16:33:46 -07:00
Committer:     Peter Zijlstra <peterz@xxxxxxxxxxxxx>
CommitterDate: Wed, 22 Mar 2023 17:09:28 +01:00

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@xxxxxxxxxx>
Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
Link: https://lkml.kernel.org/r/20230313233346.kayh4t2lpicjkpsv@treble
---
 kernel/livepatch/transition.c |  9 +++++++--
 1 file changed, 7 insertions(+), 2 deletions(-)

diff --git a/kernel/livepatch/transition.c b/kernel/livepatch/transition.c
index f1b25ec..135fc73 100644
--- 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;