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[66.187.233.206]) by smtp.gmail.com with ESMTPSA id l184sm3926233qkc.107.2020.02.14.12.33.37 (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Fri, 14 Feb 2020 12:33:37 -0800 (PST) From: Qian Cai To: akpm@linux-foundation.org Cc: elver@google.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org, Qian Cai Subject: [PATCH -next] fork: annotate a data race in vm_area_dup() Date: Fri, 14 Feb 2020 15:33:23 -0500 Message-Id: <1581712403-27243-1-git-send-email-cai@lca.pw> X-Mailer: git-send-email 1.8.3.1 X-Bogosity: Ham, tests=bogofilter, spamicity=0.042640, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: 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 The write is holding mmap_sem while changing vm_area_struct.shared.rb. Even though the read is lockless while making a copy, the clone will have its own shared.rb reinitialized. Thus, mark it as an intentional data race using the data_race() macro. Signed-off-by: Qian Cai --- kernel/fork.c | 6 +++++- 1 file changed, 5 insertions(+), 1 deletion(-) diff --git a/kernel/fork.c b/kernel/fork.c index 41f784b6203a..81bdc6e8a6cf 100644 --- a/kernel/fork.c +++ b/kernel/fork.c @@ -359,7 +359,11 @@ 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; + /* + * @orig may be modified concurrently, but the clone will be + * reinitialized. + */ + *new = data_race(*orig); INIT_LIST_HEAD(&new->anon_vma_chain); } return new;