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From:   Qian Cai <cai@lca.pw>
To:     akpm@linux-foundation.org
Cc:     catalin.marinas@arm.com, elver@google.com, linux-mm@kvack.org,
        linux-kernel@vger.kernel.org, Qian Cai <cai@lca.pw>
Subject: [PATCH -next v2] mm/kmemleak: annotate various data races obj->ptr
Date:   Thu, 13 Feb 2020 12:36:30 -0500
Message-Id: <1581615390-9720-1-git-send-email-cai@lca.pw>
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

The value of object->pointer could be accessed concurrently as noticed
by KCSAN,

 write to 0xffffb0ea683a7d50 of 4 bytes by task 23575 on cpu 12:
  do_raw_spin_lock+0x114/0x200
  debug_spin_lock_after at kernel/locking/spinlock_debug.c:91
  (inlined by) do_raw_spin_lock at kernel/locking/spinlock_debug.c:115
  _raw_spin_lock+0x40/0x50
  __handle_mm_fault+0xa9e/0xd00
  handle_mm_fault+0xfc/0x2f0
  do_page_fault+0x263/0x6f9
  page_fault+0x34/0x40

 read to 0xffffb0ea683a7d50 of 4 bytes by task 839 on cpu 60:
  crc32_le_base+0x67/0x350
  crc32_le_base+0x67/0x350:
  crc32_body at lib/crc32.c:106
  (inlined by) crc32_le_generic at lib/crc32.c:179
  (inlined by) crc32_le at lib/crc32.c:197
  kmemleak_scan+0x528/0xd90
  update_checksum at mm/kmemleak.c:1172
  (inlined by) kmemleak_scan at mm/kmemleak.c:1497
  kmemleak_scan_thread+0xcc/0xfa
  kthread+0x1e0/0x200
  ret_from_fork+0x27/0x50

 write to 0xffff939bf07b95b8 of 4 bytes by interrupt on cpu 119:
  __free_object+0x884/0xcb0
  __free_object at lib/debugobjects.c:359
  __debug_check_no_obj_freed+0x19d/0x370
  debug_check_no_obj_freed+0x41/0x4b
  slab_free_freelist_hook+0xfb/0x1c0
  kmem_cache_free+0x10c/0x3a0
  free_object_rcu+0x1ca/0x260
  rcu_core+0x677/0xcc0
  rcu_core_si+0x17/0x20
  __do_softirq+0xd9/0x57c
  run_ksoftirqd+0x29/0x50
  smpboot_thread_fn+0x222/0x3f0
  kthread+0x1e0/0x200
  ret_from_fork+0x27/0x50

 read to 0xffff939bf07b95b8 of 8 bytes by task 838 on cpu 109:
  scan_block+0x69/0x190
  scan_block at mm/kmemleak.c:1250
  kmemleak_scan+0x249/0xd90
  scan_large_block at mm/kmemleak.c:1309
  (inlined by) kmemleak_scan at mm/kmemleak.c:1434
  kmemleak_scan_thread+0xcc/0xfa
  kthread+0x1e0/0x200
  ret_from_fork+0x27/0x50

crc32() will dereference object->pointer. If a shattered value was
returned due to a data race, it will be corrected in the next scan.
scan_block() will dereference a range of addresses (e.g., percpu
sections) to search for valid pointers. Even if a data race heppens, it
will cause no issue because the code here does not care about the exact
value of a non-pointer. Thus, mark them as intentional data races using
the data_race() macro.

Signed-off-by: Qian Cai <cai@lca.pw>
---

v2: add a missing annotation.

 mm/kmemleak.c | 9 +++++++--
 1 file changed, 7 insertions(+), 2 deletions(-)

diff --git a/mm/kmemleak.c b/mm/kmemleak.c
index 3a4259eeb5a0..aa6832432d6a 100644
--- a/mm/kmemleak.c
+++ b/mm/kmemleak.c
@@ -1169,7 +1169,12 @@ static bool update_checksum(struct kmemleak_object *object)
 	u32 old_csum = object->checksum;
 
 	kasan_disable_current();
-	object->checksum = crc32(0, (void *)object->pointer, object->size);
+	/*
+	 * crc32() will dereference object->pointer. If an unstable value was
+	 * returned due to a data race, it will be corrected in the next scan.
+	 */
+	object->checksum = data_race(crc32(0, (void *)object->pointer,
+					   object->size));
 	kasan_enable_current();
 
 	return object->checksum != old_csum;
@@ -1243,7 +1248,7 @@ static void scan_block(void *_start, void *_end,
 			break;
 
 		kasan_disable_current();
-		pointer = *ptr;
+		pointer = data_race(*ptr);
 		kasan_enable_current();
 
 		untagged_ptr = (unsigned long)kasan_reset_tag((void *)pointer);
-- 
1.8.3.1