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[71.184.117.43]) by smtp.gmail.com with ESMTPSA id 65sm2232926qtf.95.2020.01.29.18.52.32 (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Wed, 29 Jan 2020 18:52:33 -0800 (PST) From: Qian Cai To: akpm@linux-foundation.org Cc: dennis@kernel.org, tj@kernel.org, cl@linux.com, elver@google.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org, Qian Cai Subject: [PATCH] mm/util: fix a data race in __vm_enough_memory() Date: Wed, 29 Jan 2020 21:51:33 -0500 Message-Id: <20200130025133.5232-1-cai@lca.pw> X-Mailer: git-send-email 2.21.0 (Apple Git-122.2) MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable X-Bogosity: Ham, tests=bogofilter, spamicity=0.001251, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: "vm_committed_as.count" could be accessed concurrently as reported by KCSAN, read to 0xffffffff923164f8 of 8 bytes by task 1268 on cpu 38: __vm_enough_memory+0x43/0x280 mm/util.c:801 mmap_region+0x1b2/0xb90 mm/mmap.c:1726 do_mmap+0x45c/0x700 vm_mmap_pgoff+0xc0/0x130 vm_mmap+0x71/0x90 elf_map+0xa1/0x1b0 load_elf_binary+0x9de/0x2180 search_binary_handler+0xd8/0x2b0 __do_execve_file+0xb61/0x1080 __x64_sys_execve+0x5f/0x70 do_syscall_64+0x91/0xb47 entry_SYSCALL_64_after_hwframe+0x49/0xbe write to 0xffffffff923164f8 of 8 bytes by task 1265 on cpu 41: percpu_counter_add_batch+0x83/0xd0 lib/percpu_counter.c:91 exit_mmap+0x178/0x220 include/linux/mman.h:68 mmput+0x10e/0x270 flush_old_exec+0x572/0xfe0 load_elf_binary+0x467/0x2180 search_binary_handler+0xd8/0x2b0 __do_execve_file+0xb61/0x1080 __x64_sys_execve+0x5f/0x70 do_syscall_64+0x91/0xb47 entry_SYSCALL_64_after_hwframe+0x49/0xbe Since only the read is operating as lockless, fix it by using READ_ONLY() for it to avoid any possible false warning due to load tearing. Signed-off-by: Qian Cai --- mm/util.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/mm/util.c b/mm/util.c index 988d11e6c17c..58cd8f28651c 100644 --- a/mm/util.c +++ b/mm/util.c @@ -798,7 +798,7 @@ int __vm_enough_memory(struct mm_struct *mm, long pag= es, int cap_sys_admin) { long allowed; =20 - VM_WARN_ONCE(percpu_counter_read(&vm_committed_as) < + VM_WARN_ONCE(READ_ONCE(vm_committed_as.count) < -(s64)vm_committed_as_batch * num_online_cpus(), "memory commitment underflow"); =20 --=20 2.21.0 (Apple Git-122.2)