[PATCH v2] kasan: Don't call find_vm_area() in RT kernel

[Waiman Long <longman@redhat.com>]

The following bug report appeared with a test run in a RT debug kernel.

[ 3359.353842] BUG: sleeping function called from invalid context at kernel/locking/spinlock_rt.c:48
[ 3359.353848] in_atomic(): 1, irqs_disabled(): 1, non_block: 0, pid: 140605, name: kunit_try_catch
[ 3359.353853] preempt_count: 1, expected: 0
  :
[ 3359.353933] Call trace:
  :
[ 3359.353955]  rt_spin_lock+0x70/0x140
[ 3359.353959]  find_vmap_area+0x84/0x168
[ 3359.353963]  find_vm_area+0x1c/0x50
[ 3359.353966]  print_address_description.constprop.0+0x2a0/0x320
[ 3359.353972]  print_report+0x108/0x1f8
[ 3359.353976]  kasan_report+0x90/0xc8
[ 3359.353980]  __asan_load1+0x60/0x70

Commit e30a0361b851 ("kasan: make report_lock a raw spinlock")
changes report_lock to a raw_spinlock_t to avoid a similar RT problem.
The print_address_description() function is called with report_lock
acquired and interrupt disabled.  However, the find_vm_area() function
still needs to acquire a spinlock_t which becomes a sleeping lock in
the RT kernel. IOW, we can't call find_vm_area() in a RT kernel and
changing report_lock to a raw_spinlock_t is not enough to completely
solve this RT kernel problem.

Fix this bug report by skipping the find_vm_area() call in this case
and just print out the address as is.

For !RT kernel, follow the example set in commit 0cce06ba859a
("debugobjects,locking: Annotate debug_object_fill_pool() wait type
violation") and use DEFINE_WAIT_OVERRIDE_MAP() to avoid a spinlock_t
inside raw_spinlock_t warning.

Fixes: e30a0361b851 ("kasan: make report_lock a raw spinlock")
Signed-off-by: Waiman Long <longman@redhat.com>
---
 mm/kasan/report.c | 47 ++++++++++++++++++++++++++++++++++-------------
 1 file changed, 34 insertions(+), 13 deletions(-)

 [v2] Encapsulate the change into a new
      kasan_print_vmalloc_info_ret_page() helper

diff --git a/mm/kasan/report.c b/mm/kasan/report.c
index 3fe77a360f1c..9580ac3f3203 100644
--- a/mm/kasan/report.c
+++ b/mm/kasan/report.c
@@ -370,6 +370,38 @@ static inline bool init_task_stack_addr(const void *addr)
 			sizeof(init_thread_union.stack));
 }
 
+/*
+ * RT kernel cannot call find_vm_area() in atomic context. For !RT kernel,
+ * prevent spinlock_t inside raw_spinlock_t warning by raising wait-type
+ * to WAIT_SLEEP.
+ *
+ * Return: page pointer or NULL
+ */
+static inline struct page *kasan_print_vmalloc_info_ret_page(void *addr)
+{
+	if (!IS_ENABLED(CONFIG_PREEMPT_RT)) {
+		static DEFINE_WAIT_OVERRIDE_MAP(vmalloc_map, LD_WAIT_SLEEP);
+		struct page *page = NULL;
+		struct vm_struct *va;
+
+		lock_map_acquire_try(&vmalloc_map);
+		va = find_vm_area(addr);
+		if (va) {
+			pr_err("The buggy address belongs to the virtual mapping at\n"
+			       " [%px, %px) created by:\n"
+			       " %pS\n",
+			       va->addr, va->addr + va->size, va->caller);
+			pr_err("\n");
+
+			page = vmalloc_to_page(addr);
+		}
+		lock_map_release(&vmalloc_map);
+		return page;
+	}
+	pr_err("The buggy address %px belongs to a vmalloc virtual mapping\n", addr);
+	return NULL;
+}
+
 static void print_address_description(void *addr, u8 tag,
 				      struct kasan_report_info *info)
 {
@@ -398,19 +430,8 @@ static void print_address_description(void *addr, u8 tag,
 		pr_err("\n");
 	}
 
-	if (is_vmalloc_addr(addr)) {
-		struct vm_struct *va = find_vm_area(addr);
-
-		if (va) {
-			pr_err("The buggy address belongs to the virtual mapping at\n"
-			       " [%px, %px) created by:\n"
-			       " %pS\n",
-			       va->addr, va->addr + va->size, va->caller);
-			pr_err("\n");
-
-			page = vmalloc_to_page(addr);
-		}
-	}
+	if (is_vmalloc_addr(addr))
+		page = kasan_print_vmalloc_info_ret_page(addr);
 
 	if (page) {
 		pr_err("The buggy address belongs to the physical page:\n");
-- 
2.48.1