@@ -798,8 +798,12 @@ int __vm_enough_memory(struct mm_struct *mm, long pages, int cap_sys_admin)
{
long allowed;
- VM_WARN_ONCE(percpu_counter_read(&vm_committed_as) <
- -(s64)vm_committed_as_batch * num_online_cpus(),
+ /*
+ * A transient decrease in the value is unlikely, so no need
+ * READ_ONCE() for vm_committed_as.count.
+ */
+ VM_WARN_ONCE(data_race(percpu_counter_read(&vm_committed_as) <
+ -(s64)vm_committed_as_batch * num_online_cpus()),
"memory commitment underflow");
vm_acct_memory(pages);
"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 The warning is almost impossible to trigger according to the commit 82f71ae4a2b8 ("mm: catch memory commitment underflow") but leave it for now to catch any possible unbalanced vm_unacct_memory() in the future. Since only the read is operating as lockless, mark it as an intentional data race using the data_race() macro to avoid modifying percpu_counter_read() and still catch unintended races elsewhere. Acked-by: Christoph Lameter <cl@linux.com> Acked-by: Dennis Zhou <dennis@kernel.org> Signed-off-by: Qian Cai <cai@lca.pw> --- v2: add some code comments. mm/util.c | 8 ++++++-- 1 file changed, 6 insertions(+), 2 deletions(-)