kasan: don't call find_vm_area() in a PREEMPT_RT kernel

The following bug report was found when running a PREEMPT_RT debug kernel.

 BUG: sleeping function called from invalid context at kernel/locking/spinlock_rt.c:48
 in_atomic(): 1, irqs_disabled(): 1, non_block: 0, pid: 140605, name: kunit_try_catch
 preempt_count: 1, expected: 0

 Call trace:
  rt_spin_lock+0x70/0x140
  find_vmap_area+0x84/0x168
  find_vm_area+0x1c/0x50
  print_address_description.constprop.0+0x2a0/0x320
  print_report+0x108/0x1f8
  kasan_report+0x90/0xc8

Since commit e30a0361b851 ("kasan: make report_lock a raw spinlock"),
report_lock was changed to raw_spinlock_t to fix another similar
PREEMPT_RT problem.  That alone isn't enough to cover other corner cases.

print_address_description() is always invoked under the report_lock.  The
context under this lock is always atomic even on PREEMPT_RT.
find_vm_area() acquires vmap_node::busy.lock which is a spinlock_t,
becoming a sleeping lock on PREEMPT_RT and must not be acquired in atomic
context.

Don't invoke find_vm_area() on PREEMPT_RT and just print the address.
Non-PREEMPT_RT builds remain unchanged.  Add a DEFINE_WAIT_OVERRIDE_MAP()
macro to tell lockdep that this lock nesting is allowed because the
PREEMPT_RT part (which is invalid) has been taken care of.  This macro was
first introduced in commit 0cce06ba859a ("debugobjects,locking: Annotate
debug_object_fill_pool() wait type violation").

Link: https://lkml.kernel.org/r/20250217204402.60533-1-longman@redhat.com
Fixes: e30a0361b851 ("kasan: make report_lock a raw spinlock")
Signed-off-by: Waiman Long <longman@redhat.com>
Suggested-by: Andrey Konovalov <andreyknvl@gmail.com>
Reviewed-by: Andrey Konovalov <andreyknvl@gmail.com>
Cc: Alexander Potapenko <glider@google.com>
Cc: Andrey Ryabinin <ryabinin.a.a@gmail.com>
Cc: Dmitriy Vyukov <dvyukov@google.com>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Mariano Pache <npache@redhat.com>
Cc: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Cc: Vincenzo Frascino <vincenzo.frascino@arm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

diff --git a/mm/kasan/report.c b/mm/kasan/report.c
index 3fe77a360f1c52a8632ff3a7900ecfd1b5b1da5a..8357e1a33699b54b3360d98f0739abffb640afef 100644 (file)
--- a/mm/kasan/report.c
+++ b/mm/kasan/report.c
@@ -370,6 +370,36 @@ static inline bool init_task_stack_addr(const void *addr)
                        sizeof(init_thread_union.stack));
 }
 
+/*
+ * This function is invoked with report_lock (a raw_spinlock) held. A
+ * PREEMPT_RT kernel cannot call find_vm_area() as it will acquire a sleeping
+ * rt_spinlock.
+ *
+ * For !RT kernel, the PROVE_RAW_LOCK_NESTING config option will print a
+ * lockdep warning for this raw_spinlock -> spinlock dependency. This config
+ * option is enabled by default to ensure better test coverage to expose this
+ * kind of RT kernel problem. This lockdep splat, however, can be suppressed
+ * by using DEFINE_WAIT_OVERRIDE_MAP() if it serves a useful purpose and the
+ * invalid PREEMPT_RT case has been taken care of.
+ */
+static inline struct vm_struct *kasan_find_vm_area(void *addr)
+{
+       static DEFINE_WAIT_OVERRIDE_MAP(vmalloc_map, LD_WAIT_SLEEP);
+       struct vm_struct *va;
+
+       if (IS_ENABLED(CONFIG_PREEMPT_RT))
+               return NULL;
+
+       /*
+        * Suppress lockdep warning and fetch vmalloc area of the
+        * offending address.
+        */
+       lock_map_acquire_try(&vmalloc_map);
+       va = find_vm_area(addr);
+       lock_map_release(&vmalloc_map);
+       return va;
+}
+
 static void print_address_description(void *addr, u8 tag,
                                      struct kasan_report_info *info)
 {
@@ -399,7 +429,7 @@ static void print_address_description(void *addr, u8 tag,
        }
 
        if (is_vmalloc_addr(addr)) {
-               struct vm_struct *va = find_vm_area(addr);
+               struct vm_struct *va = kasan_find_vm_area(addr);
 
                if (va) {
                        pr_err("The buggy address belongs to the virtual mapping at\n"
@@ -409,6 +439,8 @@ static void print_address_description(void *addr, u8 tag,
                        pr_err("\n");
 
                        page = vmalloc_to_page(addr);
+               } else {
+                       pr_err("The buggy address %px belongs to a vmalloc virtual mapping\n", addr);
                }
        }