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Sun, 22 Dec 2024 02:24:50 -0500 (EST) Received: by vm-mail (OpenSMTPD) with ESMTPSA id e2225c99 (TLSv1.3:TLS_AES_256_GCM_SHA384:256:NO); Sun, 22 Dec 2024 07:22:51 +0000 (UTC) From: Patrick Steinhardt Date: Sun, 22 Dec 2024 08:24:28 +0100 Subject: [PATCH v2 1/4] reftable/stack: don't perform auto-compaction with less than two tables Precedence: bulk X-Mailing-List: git@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Message-Id: <20241222-b4-pks-reftable-oom-fix-without-readers-v2-1-19550090d15a@pks.im> References: <20241222-b4-pks-reftable-oom-fix-without-readers-v2-0-19550090d15a@pks.im> In-Reply-To: <20241222-b4-pks-reftable-oom-fix-without-readers-v2-0-19550090d15a@pks.im> To: git@vger.kernel.org Cc: Junio C Hamano , Kristoffer Haugsbakk , "Randall S. Becker" X-Mailer: b4 0.14.2 In order to compact tables we need at least two tables. Bail out early from `reftable_stack_auto_compact()` in case we have less than two tables. In the original, `stack_table_sizes_for_compaction()` yields an array that has the same length as the number of tables. This array is then passed on to `suggest_compaction_segment()`, which returns an empty segment in case we have less than two tables. The segment is then passed to `segment_size()`, which will return `0` because both start and end of the segment are `0`. And because we only call `stack_compact_range()` in case we have a positive segment size we don't perform auto-compaction at all. Consequently, this change does not result in a user-visible change in behaviour when called with a single table. But when called with no tables this protects us against a potential out-of-memory error: `stack_table_sizes_for_compaction()` would try to allocate a zero-byte object when there aren't any tables, and that may lead to a `NULL` pointer on some platforms like NonStop which causes us to bail out with an out-of-memory error. Signed-off-by: Patrick Steinhardt --- reftable/stack.c | 3 +++ 1 file changed, 3 insertions(+) diff --git a/reftable/stack.c b/reftable/stack.c index 59fd695a12c2033ed589a21ef1c9155eeecc4641..6ca21965d8e1135d986043113d465abd14cd532c 100644 --- a/reftable/stack.c +++ b/reftable/stack.c @@ -1627,6 +1627,9 @@ int reftable_stack_auto_compact(struct reftable_stack *st) struct segment seg; uint64_t *sizes; + if (st->merged->readers_len < 2) + return 0; + sizes = stack_table_sizes_for_compaction(st); if (!sizes) return REFTABLE_OUT_OF_MEMORY_ERROR;