[PATCH] 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

The print_address_description() is run with a raw_spinlock_t acquired
and interrupt disabled. The find_vm_area() function 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. 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.

Signed-off-by: Waiman Long <longman@redhat.com>
---
 mm/kasan/report.c | 20 ++++++++++++++++++--
 1 file changed, 18 insertions(+), 2 deletions(-)

diff --git a/mm/kasan/report.c b/mm/kasan/report.c
index 3fe77a360f1c..e1ee687966aa 100644
--- a/mm/kasan/report.c
+++ b/mm/kasan/report.c
@@ -398,9 +398,20 @@ 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 (!is_vmalloc_addr(addr))
+		goto print_page;
 
+	/*
+	 * 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.
+	 */
+	if (!IS_ENABLED(CONFIG_PREEMPT_RT)) {
+		static DEFINE_WAIT_OVERRIDE_MAP(vmalloc_map, LD_WAIT_SLEEP);
+		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"
@@ -410,8 +421,13 @@ static void print_address_description(void *addr, u8 tag,
 
 			page = vmalloc_to_page(addr);
 		}
+		lock_map_release(&vmalloc_map);
+	} else {
+		pr_err("The buggy address %px belongs to a vmalloc virtual mapping\n",
+			addr);
 	}
 
+print_page:
 	if (page) {
 		pr_err("The buggy address belongs to the physical page:\n");
 		dump_page(page, "kasan: bad access detected");
-- 
2.48.1