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fix(osdtrace): make the ops map an LRU hash so leaked entries can't stop tracing #192

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fix(osdtrace): make the ops map an LRU hash so leaked entries can't stop tracing #192

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8c208b1
fix(osdtrace): don't leak ops map entries when the subop length read …
ray5273 Sep 13, 2026
6fb8d71
fix(osdtrace): make the ops map an LRU hash so leaks can't stop tracing
ray5273 Sep 13, 2026
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32 changes: 29 additions & 3 deletions src/osdtrace.bpf.c
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Original file line number Diff line number Diff line change
Expand Up @@ -14,8 +14,30 @@

char LICENSE[] SEC("license") = "Dual BSD/GPL";

/* LRU rather than plain HASH on purpose.
*
* An entry is inserted by uprobe_enqueue_op and deleted by a completion
* probe (log_op_stats, log_subop_stats, repop_commit,
* ec_submit_transaction). Ops that finish without reaching any of them
* leave their entry behind: failed reads (log_op_stats is only called for
* result >= 0, so every -ENOENT read leaks), failed writes, the
* reply_op_error paths, dup/resent ops answered from the pg log, and ops
* dropped by can_discard_request. Client tids are monotonic, so the
* orphan handling in uprobe_enqueue_op never sees these keys again.
*
* With a plain HASH the leaked entries eventually fill the map, every later
* bpf_map_update_elem fails with -E2BIG, and osdtrace silently stops
* emitting events until it is restarted.
*
* An LRU hash evicts instead of rejecting. Lookups set the reference bit,
* so ops still moving through the probes are kept over leaked entries that
* are never touched again. An op that sits untouched long enough while the
* map is under pressure (e.g. waiting in the op queue) can still be evicted
* and go missing from the output, and eviction can start before max_entries
* is reached because of the per-CPU free lists.
*/
struct {
__uint(type, BPF_MAP_TYPE_HASH);
__uint(type, BPF_MAP_TYPE_LRU_HASH);
__type(key, struct op_k);
__type(value, struct op_v);
__uint(max_entries, 8192);
Expand Down Expand Up @@ -744,8 +766,10 @@ int uprobe_log_subop_stats(struct pt_regs *ctx)
if (NULL == vp) return 0;

__u64 len = 0;
if (read_hprobe_varfield(ctx, varid++, &len, sizeof(len)) != 0)
if (read_hprobe_varfield(ctx, varid++, &len, sizeof(len)) != 0) {
bpf_map_delete_elem(&ops, &key);
return 0;
}

vp->wb = len;
vp->reply_stamp = bpf_ktime_get_boot_ns();
Expand Down Expand Up @@ -837,8 +861,10 @@ int uprobe_repop_commit(struct pt_regs *ctx)
}

__u64 len = 0;
if (read_hprobe_varfield(ctx, varid++, &len, sizeof(len)) != 0)
if (read_hprobe_varfield(ctx, varid++, &len, sizeof(len)) != 0) {
bpf_map_delete_elem(&ops, &key);
return 0;
}

vp->wb = len;
vp->reply_stamp = bpf_ktime_get_boot_ns();
Expand Down