So far, QHT functions assume that the passed qht has previously been
initialized--otherwise they segfault.
This patch makes an exception for qht_statistics_init, with the goal
of simplifying calling code. For instance, qht_statistics_init is
called from the 'info jit' dump, and given that under KVM the TB qht
is never initialized, we get a segfault. Thus, instead of complicating
the 'info jit' code with additional checks, let's allow passing an
uninitialized qht to qht_statistics_init.
While at it, add a test for this to test-qht.
Before the patch (for $ qemu -enable-kvm [...]):
(qemu) info jit
[...]
direct jump count 0 (0%) (2 jumps=0 0%)
Program received signal SIGSEGV, Segmentation fault.
After the patch:
(qemu) info jit
[...]
direct jump count 0 (0%) (2 jumps=0 0%)
TB hash buckets 0/0 (-nan% head buckets used)
TB hash occupancy nan% avg chain occ. Histogram: (null)
TB hash avg chain nan buckets. Histogram: (null)
[...]
Reported by: Changlong Xie <xiecl.f...@cn.fujitsu.com>
Signed-off-by: Emilio G. Cota <c...@braap.org>
---
tests/test-qht.c | 4 ++++
util/qht.c | 7 ++++++-
2 files changed, 10 insertions(+), 1 deletion(-)
diff --git a/tests/test-qht.c b/tests/test-qht.c
index c8eb930..e2f9e14 100644
--- a/tests/test-qht.c
+++ b/tests/test-qht.c
@@ -96,8 +96,12 @@ static void iter_check(unsigned int count)
static void qht_do_test(unsigned int mode, size_t init_entries)
{
+ /* under KVM we might fetch stats from an uninitialized qht */
+ check_n(0);
+
qht_init(&ht, 0, mode);
+ check_n(0);
insert(0, N);
check(0, N, true);
check_n(N);
diff --git a/util/qht.c b/util/qht.c
index 6f74909..0cb95e2 100644
--- a/util/qht.c
+++ b/util/qht.c
@@ -783,11 +783,16 @@ void qht_statistics_init(struct qht *ht, struct qht_stats
*stats)
map = atomic_rcu_read(&ht->map);
- stats->head_buckets = map->n_buckets;
stats->used_head_buckets = 0;
stats->entries = 0;
qdist_init(&stats->chain);
qdist_init(&stats->occupancy);
+ /* bail out if the qht has not yet been initialized */
+ if (unlikely(map == NULL)) {
+ stats->head_buckets = 0;
+ return;
+ }
+ stats->head_buckets = map->n_buckets;
for (i = 0; i < map->n_buckets; i++) {
struct qht_bucket *head = &map->buckets[i];
--
1.9.1
