ftrace: Synchronize the initialization of ftrace_opsgrafted

There's some internal state that ftrace_ops needs to have set, but since
it can be declared outside of the ftrace.c code, it calls
ftrace_ops_init() on the ops in every global function. The issue is that
if two tasks call it on the same ops at the same time it is possible to
have the initialization of one corrupt the initialization of the other
call.

Create a ops_mutex to use to synchronize every initialization of the
ftrace_ops. The mutex is taken within checking the ftrace_ops flag that
states it was initializied but the flag is checked again after the mutex
has been taken. Checking first outside the mutex allows it to shortcut
having to take the mutex. But then the check needs to be done again after
the mute is taken in case of races.

Cc: stable@vger.kernel.org
Link: https://patch.msgid.link/20260902095501.6b59af20@gandalf.local.home
Fixes: f04f24fb7e48d ("ftrace, kprobes: Fix a deadlock on ftrace_regex_lock")
Reported-by: sashiko-bot@kernel.org
Close: https://lore.kernel.org/all/20260829025528.49A831F000E9@smtp.kernel.org/
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>

1 files changed, 67 insertions, 0 deletions

diff --git a/arch/arm64/mm/pgd.c b/arch/arm64/mm/pgd.c
new file mode 100644
index 000000000..bf5110b91
--- /dev/null
+++ b/arch/arm64/mm/pgd.c
@@ -0,0 +1,67 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * PGD allocation/freeing
+ *
+ * Copyright (C) 2012 ARM Ltd.
+ * Author: Catalin Marinas <catalin.marinas@arm.com>
+ */
+
+#include <linux/mm.h>
+#include <linux/gfp.h>
+#include <linux/highmem.h>
+#include <linux/slab.h>
+
+#include <asm/pgalloc.h>
+#include <asm/page.h>
+#include <asm/tlbflush.h>
+
+static struct kmem_cache *pgd_cache __ro_after_init;
+
+static bool pgdir_is_page_size(void)
+{
+	if (PGD_SIZE == PAGE_SIZE)
+		return true;
+	if (CONFIG_PGTABLE_LEVELS == 4)
+		return !pgtable_l4_enabled();
+	if (CONFIG_PGTABLE_LEVELS == 5)
+		return !pgtable_l5_enabled();
+	return false;
+}
+
+pgd_t *pgd_alloc(struct mm_struct *mm)
+{
+	gfp_t gfp = GFP_PGTABLE_USER;
+
+	if (pgdir_is_page_size())
+		return __pgd_alloc(mm, 0);
+	else
+		return kmem_cache_alloc(pgd_cache, gfp);
+}
+
+void pgd_free(struct mm_struct *mm, pgd_t *pgd)
+{
+	if (pgdir_is_page_size())
+		__pgd_free(mm, pgd);
+	else
+		kmem_cache_free(pgd_cache, pgd);
+}
+
+void __init pgtable_cache_init(void)
+{
+	if (pgdir_is_page_size())
+		return;
+
+#ifdef CONFIG_ARM64_PA_BITS_52
+	/*
+	 * With 52-bit physical addresses, the architecture requires the
+	 * top-level table to be aligned to at least 64 bytes.
+	 */
+	BUILD_BUG_ON(!IS_ALIGNED(PGD_SIZE, 64));
+#endif
+
+	/*
+	 * Naturally aligned pgds required by the architecture.
+	 */
+	pgd_cache = kmem_cache_create("pgd_cache", PGD_SIZE, PGD_SIZE,
+				      SLAB_PANIC, NULL);
+}