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tools/memleak: Fix the data error caused by the same key in map (#4970)
Followings are the way to generate data error issue and the result after applying this patch.
File test.cpp
#include <iostream>
#include <thread>
#include <unistd.h>
void alloc() {
for (int i = 0; i < 100000; ++i) {
int* a = (int*)malloc(4);
}
}
int main() {
sleep(100);
std::thread t1 {&alloc};
std::thread t2 {&alloc};
t1.join();
t2.join();
sleep(50);
return 0;
}
Build the test file
$ g++ -g -o test -lpthread test.cpp
Run this with --combined-only:
sudo ./memleak.py -c ./test --combined-only
Executing './test' and tracing the resulting process.
Attaching to pid 194273, Ctrl+C to quit.
[23:36:43] Top 10 stacks with outstanding allocations:
576 bytes in 2 allocations from stack
__GI__dl_allocate_tls+0x2c [ld-2.28.so]
799992 bytes in 199998 allocations from stack
alloc()+0x22 [test]
void std::__invoke_impl<void, void (*)()>(std::__invoke_other, void (*&&)())+0x1d [test]
std::__invoke_result<void (*)()>::type std::__invoke<void (*)()>(void (*&&)())+0x20 [test]
decltype (__invoke((_S_declval<0ul>)())) std::thread::_Invoker<std::tuple<void (*)()> >::_M_invoke<0ul>(std::_Index_tuple<0ul>)+0x28 [test]
std::thread::_Invoker<std::tuple<void (*)()> >::operator()()+0x18 [test]
std::thread::_State_impl<std::thread::_Invoker<std::tuple<void (*)()> > >::_M_run()+0x1c [test]
[unknown] [libstdc++.so.6.0.25]
8392704 bytes in 1 allocations from stack
pthread_create+0x893 [libpthread-2.28.so]
std::thread::_M_start_thread(std::unique_ptr<std::thread::_State, std::default_delete<std::thread::_State> >, void (*)())+0x19 [libstdc++.so.6.0.25]
main+0x49 [test]
__libc_start_main+0xf3 [libc-2.28.so]
[unknown]
8392704 bytes in 1 allocations from stack
pthread_create+0x893 [libpthread-2.28.so]
std::thread::_M_start_thread(std::unique_ptr<std::thread::_State, std::default_delete<std::thread::_State> >, void (*)())+0x19 [libstdc++.so.6.0.25]
main+0x2e [test]
__libc_start_main+0xf3 [libc-2.28.so]
[unknown]
134217728 bytes in 1 allocations from stack
new_heap+0xa7 [libc-2.28.so]
Problem:
We can see 799992 bytes alloced in 199998 allocations from stack while when we read the code, we will find that there should be 800000 bytes alloced in 200000 allocations.
Reason:
After Tracing, we can find that `malloc()` may call `mmap()`, so there will be two continuous call of `gen_alloc_enter(struct pt_regs *ctx, size_t size)` in a same process.
For example, in our `test` process, when it first call `int* a = (int*)malloc(4);`, `gen_alloc_enter(struct pt_regs *ctx, size_t size)` will be called, and there will be a
pair of data <tid, 4> in BPF_HASH sizes; then a `mmap()` will be called, also `gen_alloc_enter(struct pt_regs *ctx, size_t size)` be called, which make <tid, 4> change into
<tid, MMAP_SIZE>. This will make the call of `gen_alloc_exit()` for the first `malloc()` will return early because the `tid` key will be deleted after the call of
`gen_alloc_exit()` caused by `mmap()`, which finally cause data error.
The callchain:
malloc()->gen_alloc_enter()->mmap()->gen_alloc_enter()->mmap_return()->gen_alloc_exit()->malloc_return()->gen_alloc_exit();
Solution:
We can add type_index to help distinguish calling sources and reduce key conflicts.
After Applying this patch, run memleak.py with --combined-only:
sudo ./memleak.py -c ./test --combined-only
Executing './test' and tracing the resulting process.
Attaching to pid 194659, Ctrl+C to quit.
[23:37:16] Top 10 stacks with outstanding allocations:
576 bytes in 2 allocations from stack
__GI__dl_allocate_tls+0x2c [ld-2.28.so]
800000 bytes in 200000 allocations from stack
alloc()+0x22 [test]
void std::__invoke_impl<void, void (*)()>(std::__invoke_other, void (*&&)())+0x1d [test]
std::__invoke_result<void (*)()>::type std::__invoke<void (*)()>(void (*&&)())+0x20 [test]
decltype (__invoke((_S_declval<0ul>)())) std::thread::_Invoker<std::tuple<void (*)()> >::_M_invoke<0ul>(std::_Index_tuple<0ul>)+0x28 [test]
std::thread::_Invoker<std::tuple<void (*)()> >::operator()()+0x18 [test]
std::thread::_State_impl<std::thread::_Invoker<std::tuple<void (*)()> > >::_M_run()+0x1c [test]
[unknown] [libstdc++.so.6.0.25]
8392704 bytes in 1 allocations from stack
pthread_create+0x893 [libpthread-2.28.so]
std::thread::_M_start_thread(std::unique_ptr<std::thread::_State, std::default_delete<std::thread::_State> >, void (*)())+0x19 [libstdc++.so.6.0.25]
main+0x49 [test]
__libc_start_main+0xf3 [libc-2.28.so]
[unknown]
8392704 bytes in 1 allocations from stack
pthread_create+0x893 [libpthread-2.28.so]
std::thread::_M_start_thread(std::unique_ptr<std::thread::_State, std::default_delete<std::thread::_State> >, void (*)())+0x19 [libstdc++.so.6.0.25]
main+0x2e [test]
__libc_start_main+0xf3 [libc-2.28.so]
[unknown]
134217728 bytes in 1 allocations from stack
new_heap+0xa7 [libc-2.28.so]- Loading branch information
