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From: "peadar at arista dot com" <sourceware-bugzilla@sourceware.org>
To: glibc-bugs@sourceware.org
Subject: [Bug libc/26641] New: Memory leak in _dl_scope_free
Date: Mon, 21 Sep 2020 16:25:48 +0000
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https://sourceware.org/bugzilla/show_bug.cgi?id=3D26641

            Bug ID: 26641
           Summary: Memory leak in _dl_scope_free
           Product: glibc
           Version: unspecified
            Status: UNCONFIRMED
          Severity: normal
          Priority: P2
         Component: libc
          Assignee: unassigned at sourceware dot org
          Reporter: peadar at arista dot com
                CC: drepper.fsp at gmail dot com
  Target Milestone: ---

Created attachment 12852
  --> https://sourceware.org/bugzilla/attachment.cgi?id=3D12852&action=3Ded=
it
Tentative patch to fix/explain issue.

You can reproduce this issue running valgrind on a multithreaded program th=
at
opens a large number of shared libraries, and the attached patch solves it
locally.

_dl_scope_free is used when releasing a "scope".=20

This either
  * frees the scope directly (unthreaded case),
  * creates a new dl_scope_free_list for the scope (threaded case, first ca=
ll),=20
  * adds the scope to the existing scope_free_list (second and successive
call),=20
  * eventually free's the content of the scope_free_list (when
dl_scope_free_list has filled).

The intent, I assume, is to amortize the time spent synchronizing with other
threads in THREAD_GSCOPE_WAIT by just doing it once for a bunch of calls to
"free".

The problem is in the final case, when the space in dl_scope_free_list is
exhausted, the appropriate synchronization is performed , all the existing
scopes on the free list are free'd, *however*, the passed "old" scope is no=
t.

There's also a cosmetic issue in dl-libc.c in the __libc_freeres callback -
When cleaning up with the _dl_scope_free_list, only the list itself is free=
'd.
The entries it points to are not.

--=20
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