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HPA: Fix infinite purging loop

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One of the condition to start purging is `hpa_hugify_blocked_by_ndirty`
function call returns true. This can happen in cases where we have no
dirty memory for this shard at all. In this case purging loop will be an
infinite loop.

`hpa_hugify_blocked_by_ndirty` was introduced at 0f6c420, but at that
time purging loop has different form and additional `break` was not
required. Purging loop form was re-written at 6630c5989, but additional
exit condition wasn't added there at the time.

Repo code was shared by Patrik Dokoupil at [1], I stripped it down to
minimum to reproduce issue in jemalloc unit tests.

[1]: https://github.com/jemalloc/jemalloc/pull/2533
This commit is contained in:
Dmitry Ilvokhin 2024-04-04 10:02:08 -07:00 • committed by Qi Wang
parent fa451de17f
commit 47d69b4eab
2 changed files with 57 additions and 4 deletions
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11
src/hpa.c
View file

@ -537,9 +537,16 @@ hpa_shard_maybe_do_deferred_work(tsdn_t *tsdn, hpa_shard_t *shard,
purged = false;
while (hpa_should_purge(tsdn, shard) && nops < max_ops) {
purged = hpa_try_purge(tsdn, shard);
if (purged) {
nops++;
if (!purged) {
/*
* It is fine if we couldn't purge as sometimes
* we try to purge just to unblock
* hugification, but there is maybe no dirty
* pages at all at the moment.
*/
break;
}
nops++;
}
hugified = hpa_try_hugify(tsdn, shard);
if (hugified) {

50
test/unit/hpa.c
View file

@ -24,7 +24,7 @@ struct test_data_s {
static hpa_shard_opts_t test_hpa_shard_opts_default = {
/* slab_max_alloc */
ALLOC_MAX,
/* hugification threshold */
/* hugification_threshold */
HUGEPAGE,
/* dirty_mult */
FXP_INIT_PERCENT(25),
@ -36,6 +36,21 @@ static hpa_shard_opts_t test_hpa_shard_opts_default = {
5 * 1000,
};
static hpa_shard_opts_t test_hpa_shard_opts_purge = {
/* slab_max_alloc */
HUGEPAGE,
/* hugification_threshold */
0.9 * HUGEPAGE,
/* dirty_mult */
FXP_INIT_PERCENT(11),
/* deferral_allowed */
true,
/* hugify_delay_ms */
0,
/* min_purge_interval_ms */
5 * 1000,
};
static hpa_shard_t *
create_test_data(const hpa_hooks_t *hooks, hpa_shard_opts_t *opts) {
bool err;
@ -452,6 +467,36 @@ TEST_BEGIN(test_defer_time) {
}
TEST_END
TEST_BEGIN(test_purge_no_infinite_loop) {
test_skip_if(!hpa_supported());
hpa_shard_t *shard = create_test_data(&hpa_hooks_default,
&test_hpa_shard_opts_purge);
tsdn_t *tsdn = tsd_tsdn(tsd_fetch());
/*
* This is not arbitrary value, it is chosen to met hugification
* criteria for huge page and at the same time do not allow hugify page
* without triggering a purge.
*/
const size_t npages =
test_hpa_shard_opts_purge.hugification_threshold / PAGE + 1;
const size_t size = npages * PAGE;
bool deferred_work_generated = false;
edata_t *edata = pai_alloc(tsdn, &shard->pai, size, PAGE,
/* zero */ false, /* guarded */ false, /* frequent_reuse */ false,
&deferred_work_generated);
expect_ptr_not_null(edata, "Unexpected alloc failure");
hpa_shard_do_deferred_work(tsdn, shard);
/* hpa_shard_do_deferred_work should not stuck in a purging loop */
destroy_test_data(shard);
}
TEST_END
int
main(void) {
/*
@ -470,5 +515,6 @@ main(void) {
test_alloc_max,
test_stress,
test_alloc_dalloc_batch,
test_defer_time);
test_defer_time,
test_purge_no_infinite_loop);
}