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qht: do not segfault when gathering stats from an uninitialized qht

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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 the "TB hash buckets", "TB hash occupancy"
and "TB hash avg chain" lines are omitted.
(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.fnst@cn.fujitsu.com>
Signed-off-by: Emilio G. Cota <cota@braap.org>
Message-Id: <1469205390-14369-1-git-send-email-cota@braap.org>
[Extract printing statistics to an entirely separate function. - Paolo]
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
This commit is contained in:
Emilio G. Cota 2016-07-22 12:36:30 -04:00 • committed by Paolo Bonzini
parent 767db021bc
commit 7266ae91a1
3 changed files with 49 additions and 32 deletions
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7
util/qht.c
View file

@ -789,11 +789,16 @@ 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];