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base: fix potential memory leak in allocator_avl

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When used by the 'Allocator_avl' the slab allocator's backing store is
dynamically disabled and re-enabled while adding/freeing ranges.
However, during those operations, slab entries can be freed. This,
in turn, can result in the release of a slab block (when the freed slab
entry happens to be the last entry of the block). In this corner case,
'Slab::_release_backing_store' operation has no effect because no
backing-store allocator is set. As a result, the block is no longer
referenced but not physically freed.

The patch fixes the problem by skipping '_free_curr_sb' whenever
no backing store is defined. So the completely empty block remains
in the working set.

Thanks to Peter for reporting and fixing this issue!

Fixes #4367
This commit is contained in:
Norman Feske 2022-01-06 11:34:14 +01:00 committed by Christian Helmuth
parent 3bbe7d9d07
commit 88ca8d1a72
1 changed files with 2 additions and 1 deletions
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3
repos/base/src/lib/base/slab.cc
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@ -438,7 +438,8 @@ void Slab::_free(void *addr)
_curr_sb = █
while (_total_avail > 2*_entries_per_block
&& _num_blocks > 1
&& _curr_sb->avail() == _entries_per_block) {
&& _curr_sb->avail() == _entries_per_block
&& _backing_store) {
_free_curr_sb();
}
}