From: Qian Cai <cai@lca.pw>
To: paulmck@kernel.org
Cc: akpm@linux-foundation.org, kirill@shutemov.name,
elver@google.com, peterz@infradead.org, linux-mm@kvack.org,
linux-kernel@vger.kernel.org, Qian Cai <cai@lca.pw>
Subject: [PATCH -next v2] fork: annotate a data race in vm_area_dup()
Date: Wed, 19 Feb 2020 09:28:15 -0500 [thread overview]
Message-ID: <1582122495-12885-1-git-send-email-cai@lca.pw> (raw)
struct vm_area_struct could be accessed concurrently as noticed by
KCSAN,
write to 0xffff9cf8bba08ad8 of 8 bytes by task 14263 on cpu 35:
vma_interval_tree_insert+0x101/0x150:
rb_insert_augmented_cached at include/linux/rbtree_augmented.h:58
(inlined by) vma_interval_tree_insert at mm/interval_tree.c:23
__vma_link_file+0x6e/0xe0
__vma_link_file at mm/mmap.c:629
vma_link+0xa2/0x120
mmap_region+0x753/0xb90
do_mmap+0x45c/0x710
vm_mmap_pgoff+0xc0/0x130
ksys_mmap_pgoff+0x1d1/0x300
__x64_sys_mmap+0x33/0x40
do_syscall_64+0x91/0xc44
entry_SYSCALL_64_after_hwframe+0x49/0xbe
read to 0xffff9cf8bba08a80 of 200 bytes by task 14262 on cpu 122:
vm_area_dup+0x6a/0xe0
vm_area_dup at kernel/fork.c:362
__split_vma+0x72/0x2a0
__split_vma at mm/mmap.c:2661
split_vma+0x5a/0x80
mprotect_fixup+0x368/0x3f0
do_mprotect_pkey+0x263/0x420
__x64_sys_mprotect+0x51/0x70
do_syscall_64+0x91/0xc44
entry_SYSCALL_64_after_hwframe+0x49/0xbe
vm_area_dup() blindly copies all fields of original VMA to the new one.
This includes coping vm_area_struct::shared.rb which is normally
protected by i_mmap_lock. But this is fine because the read value will
be overwritten on the following __vma_link_file() under proper
protection. Thus, mark it as an intentional data race and insert a few
assertions for the fields that should not be modified concurrently.
Signed-off-by: Qian Cai <cai@lca.pw>
---
v2: Insert a few assertions thanks to Marco.
Update the commit log thanks to Kirill.
kernel/fork.c | 8 +++++++-
1 file changed, 7 insertions(+), 1 deletion(-)
diff --git a/kernel/fork.c b/kernel/fork.c
index cb2ae49e497e..67a5d691ffa8 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -359,7 +359,13 @@ struct vm_area_struct *vm_area_dup(struct vm_area_struct *orig)
struct vm_area_struct *new = kmem_cache_alloc(vm_area_cachep, GFP_KERNEL);
if (new) {
- *new = *orig;
+ ASSERT_EXCLUSIVE_WRITER(orig->vm_flags);
+ ASSERT_EXCLUSIVE_WRITER(orig->vm_file);
+ /*
+ * orig->shared.rb may be modified concurrently, but the clone
+ * will be reinitialized.
+ */
+ *new = data_race(*orig);
INIT_LIST_HEAD(&new->anon_vma_chain);
new->vm_next = new->vm_prev = NULL;
}
--
1.8.3.1
next reply other threads:[~2020-02-19 14:28 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-02-19 14:28 Qian Cai [this message]
2020-02-19 19:04 ` [PATCH -next v2] fork: annotate a data race in vm_area_dup() Paul E. McKenney
2020-02-20 12:56 ` Kirill A. Shutemov
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