libltdl leaks when unloading plugins depending on external lib

[Brice Goglin]

Hello,

I am fixing leaks in one of my software projects that embeds libltdl
2.4.2 to load plugins. I noticed that when the plugin depends on the
dynamic library that the main program doesn't depend on, valgrind
reports some leaks.

We created a small testcase reproducing the problem. It's available at
    http://www.open-mpi.org/~jsquyres/ltdl-valgrind-leaks/
Just download it, ./configure, make, make install and then run valgrind
as shown below.

If we remove the reference to pthread in the plugin, the leaks go away.

I assume that libltdl doesn't unload these dependency libraries when the
plugin is unloaded. But I'd like to know if these leaks are expected or
not. The good news is that these leaks do not depend on the number of
times this code is executed within the program, so the leaked size
should be constant.

Regards
Brice Goglin


$ valgrind --leak-check=full --show-reachable=yes ./runme
==1446== Memcheck, a memory error detector
==1446== Copyright (C) 2002-2011, and GNU GPL'd, by Julian Seward et al.
==1446== Using Valgrind-3.7.0 and LibVEX; rerun with -h for copyright info
==1446== Command: ./runme
==1446== 
==1446== 
==1446== HEAP SUMMARY:
==1446==     in use at exit: 1,748 bytes in 6 blocks
==1446==   total heap usage: 52 allocs, 46 frees, 7,393 bytes allocated
==1446== 
==1446== 32 bytes in 1 blocks are still reachable in loss record 1 of 6
==1446==    at 0x402894D: malloc (in 
/usr/lib/valgrind/vgpreload_memcheck-amd64-linux.so)
==1446==    by 0x4013197: _dl_close_worker (dl-close.c:374)
==1446==    by 0x401371D: _dl_close (dl-close.c:754)
==1446==    by 0x400D925: _dl_catch_error (dl-error.c:178)
==1446==    by 0x4E2D2EB: _dlerror_run (dlerror.c:164)
==1446==    by 0x4E2D00E: dlclose (dlclose.c:48)
==1446==    by 0x4C297BB: ??? (in /usr/lib/x86_64-linux-gnu/libltdl.so.7.3.0)
==1446==    by 0x4C276EC: lt_dlclose (in 
/usr/lib/x86_64-linux-gnu/libltdl.so.7.3.0)
==1446==    by 0x400C6F: main (runme.c:31)
==1446== 
==1446== 38 bytes in 1 blocks are still reachable in loss record 2 of 6
==1446==    at 0x402894D: malloc (in 
/usr/lib/valgrind/vgpreload_memcheck-amd64-linux.so)
==1446==    by 0x4004E21: local_strdup (dl-load.c:162)
==1446==    by 0x4007929: _dl_map_object (dl-load.c:2373)
==1446==    by 0x400CF61: openaux (dl-deps.c:65)
==1446==    by 0x400D925: _dl_catch_error (dl-error.c:178)
==1446==    by 0x400C02B: _dl_map_object_deps (dl-deps.c:247)
==1446==    by 0x4011EB7: dl_open_worker (dl-open.c:263)
==1446==    by 0x400D925: _dl_catch_error (dl-error.c:178)
==1446==    by 0x4011899: _dl_open (dl-open.c:633)
==1446==    by 0x4E2CF65: dlopen_doit (dlopen.c:67)
==1446==    by 0x400D925: _dl_catch_error (dl-error.c:178)
==1446==    by 0x4E2D2EB: _dlerror_run (dlerror.c:164)
==1446== 
==1446== 38 bytes in 1 blocks are still reachable in loss record 3 of 6
==1446==    at 0x402894D: malloc (in 
/usr/lib/valgrind/vgpreload_memcheck-amd64-linux.so)
==1446==    by 0x400AA85: _dl_new_object (dl-object.c:161)
==1446==    by 0x4005FB5: _dl_map_object_from_fd (dl-load.c:957)
==1446==    by 0x40076B7: _dl_map_object (dl-load.c:2468)
==1446==    by 0x400CF61: openaux (dl-deps.c:65)
==1446==    by 0x400D925: _dl_catch_error (dl-error.c:178)
==1446==    by 0x400C02B: _dl_map_object_deps (dl-deps.c:247)
==1446==    by 0x4011EB7: dl_open_worker (dl-open.c:263)
==1446==    by 0x400D925: _dl_catch_error (dl-error.c:178)
==1446==    by 0x4011899: _dl_open (dl-open.c:633)
==1446==    by 0x4E2CF65: dlopen_doit (dlopen.c:67)
==1446==    by 0x400D925: _dl_catch_error (dl-error.c:178)
==1446== 
==1446== 56 bytes in 1 blocks are still reachable in loss record 4 of 6
==1446==    at 0x402894D: malloc (in 
/usr/lib/valgrind/vgpreload_memcheck-amd64-linux.so)
==1446==    by 0x400C0DC: _dl_map_object_deps (dl-deps.c:470)
==1446==    by 0x4011EB7: dl_open_worker (dl-open.c:263)
==1446==    by 0x400D925: _dl_catch_error (dl-error.c:178)
==1446==    by 0x4011899: _dl_open (dl-open.c:633)
==1446==    by 0x4E2CF65: dlopen_doit (dlopen.c:67)
==1446==    by 0x400D925: _dl_catch_error (dl-error.c:178)
==1446==    by 0x4E2D2EB: _dlerror_run (dlerror.c:164)
==1446==    by 0x4E2CEE0: dlopen@@GLIBC_2.2.5 (dlopen.c:88)
==1446==    by 0x4C29806: ??? (in /usr/lib/x86_64-linux-gnu/libltdl.so.7.3.0)
==1446==    by 0x4C26919: ??? (in /usr/lib/x86_64-linux-gnu/libltdl.so.7.3.0)
==1446==    by 0x4C26B97: ??? (in /usr/lib/x86_64-linux-gnu/libltdl.so.7.3.0)
==1446== 
==1446== 408 bytes in 1 blocks are still reachable in loss record 5 of 6
==1446==    at 0x4027034: calloc (in 
/usr/lib/valgrind/vgpreload_memcheck-amd64-linux.so)
==1446==    by 0x400F4D3: _dl_check_map_versions (dl-version.c:299)
==1446==    by 0x401238E: dl_open_worker (dl-open.c:269)
==1446==    by 0x400D925: _dl_catch_error (dl-error.c:178)
==1446==    by 0x4011899: _dl_open (dl-open.c:633)
==1446==    by 0x4E2CF65: dlopen_doit (dlopen.c:67)
==1446==    by 0x400D925: _dl_catch_error (dl-error.c:178)
==1446==    by 0x4E2D2EB: _dlerror_run (dlerror.c:164)
==1446==    by 0x4E2CEE0: dlopen@@GLIBC_2.2.5 (dlopen.c:88)
==1446==    by 0x4C29806: ??? (in /usr/lib/x86_64-linux-gnu/libltdl.so.7.3.0)
==1446==    by 0x4C26919: ??? (in /usr/lib/x86_64-linux-gnu/libltdl.so.7.3.0)
==1446==    by 0x4C26B97: ??? (in /usr/lib/x86_64-linux-gnu/libltdl.so.7.3.0)
==1446== 
==1446== 1,176 bytes in 1 blocks are still reachable in loss record 6 of 6
==1446==    at 0x4027034: calloc (in 
/usr/lib/valgrind/vgpreload_memcheck-amd64-linux.so)
==1446==    by 0x400A80E: _dl_new_object (dl-object.c:77)
==1446==    by 0x4005FB5: _dl_map_object_from_fd (dl-load.c:957)
==1446==    by 0x40076B7: _dl_map_object (dl-load.c:2468)
==1446==    by 0x400CF61: openaux (dl-deps.c:65)
==1446==    by 0x400D925: _dl_catch_error (dl-error.c:178)
==1446==    by 0x400C02B: _dl_map_object_deps (dl-deps.c:247)
==1446==    by 0x4011EB7: dl_open_worker (dl-open.c:263)
==1446==    by 0x400D925: _dl_catch_error (dl-error.c:178)
==1446==    by 0x4011899: _dl_open (dl-open.c:633)
==1446==    by 0x4E2CF65: dlopen_doit (dlopen.c:67)
==1446==    by 0x400D925: _dl_catch_error (dl-error.c:178)
==1446== 
==1446== LEAK SUMMARY:
==1446==    definitely lost: 0 bytes in 0 blocks
==1446==    indirectly lost: 0 bytes in 0 blocks
==1446==      possibly lost: 0 bytes in 0 blocks
==1446==    still reachable: 1,748 bytes in 6 blocks
==1446==         suppressed: 0 bytes in 0 blocks
==1446== 
==1446== For counts of detected and suppressed errors, rerun with: -v
==1446== ERROR SUMMARY: 0 errors from 0 contexts (suppressed: 4 from 4)