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mm/slub: fix memory leak in free_to_pcs_bulk()

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The commit 989b09b739 ("slab: skip percpu sheaves for remote object
freeing") introduced the remote_objects array in free_to_pcs_bulk() to
skip sheaves when objects from a remote node are freed.

However, the array is flushed only when:
  1) the array becomes full (++remote_nr >= PCS_BATCH_MAX), or
  2) slab_free_hook() returns false and size becomes zero.

When neither of the conditions is met, objects in the array are leaked.
This resulted in a memory leak [1], where 82 GiB of memory was allocated
for the maple_node cache.

Flush the array after successfully freeing objects to sheaves
in the do_free: path.

In the meantime, move the snippet if (!size) goto flush_remote; outside
the while loop for readability. Let's say all objects in the array are
from a remote node: then we acquire s->cpu_sheaves->lock and try to free
an object even when size is zero. This doesn't appear to be harmful,
but isn't really readable.

Reported-by: Tytus Rogalewski <admin@simplepod.ai>
Closes: https://bugzilla.kernel.org/show_bug.cgi?id=220765 [1]
Closes: https://lore.kernel.org/linux-mm/20251107094809.12e9d705b7bf4815783eb184@linux-foundation.org
Closes: https://lore.kernel.org/all/aRGDTwbt2EIz2CYn@hyeyoo
Fixes: 989b09b739 ("slab: skip percpu sheaves for remote object freeing")
Signed-off-by: Harry Yoo <harry.yoo@oracle.com>
Link: https://patch.msgid.link/20251111125331.12246-1-harry.yoo@oracle.com
Acked-by: Liam R. Howlett <Liam.Howlett@oracle.com>
Tested-by: Darrick J. Wong <djwong@kernel.org>
Tested-by: Tytus Rogalewski <admin@simplepod.ai>
Signed-off-by: Vlastimil Babka <vbabka@suse.cz>
This commit is contained in:
Harry Yoo
2025-11-11 21:53:31 +09:00
committed by Vlastimil Babka
parent c379b745e1
commit cbcff934fa
1 changed files with 6 additions and 2 deletions
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8
mm/slub.c
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@@ -6332,8 +6332,6 @@ next_remote_batch:
if (unlikely(!slab_free_hook(s, p[i], init, false))) {
p[i] = p[--size];
if (!size)
goto flush_remote;
continue;
}
@@ -6348,6 +6346,9 @@ next_remote_batch:
i++;
}
if (!size)
goto flush_remote;
next_batch:
if (!local_trylock(&s->cpu_sheaves->lock))
goto fallback;
@@ -6402,6 +6403,9 @@ do_free:
goto next_batch;
}
if (remote_nr)
goto flush_remote;
return;
no_empty: