From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:55577) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1bQdRR-000545-5m for qemu-devel@nongnu.org; Fri, 22 Jul 2016 12:36:50 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1bQdRM-0002Yx-Ic for qemu-devel@nongnu.org; Fri, 22 Jul 2016 12:36:48 -0400 Received: from out5-smtp.messagingengine.com ([66.111.4.29]:59156) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1bQdRK-0002Vf-8y for qemu-devel@nongnu.org; Fri, 22 Jul 2016 12:36:44 -0400 From: "Emilio G. Cota" Date: Fri, 22 Jul 2016 12:36:30 -0400 Message-Id: <1469205390-14369-1-git-send-email-cota@braap.org> In-Reply-To: <5791E191.4010404@cn.fujitsu.com> References: <5791E191.4010404@cn.fujitsu.com> Subject: [Qemu-devel] [PATCH] qht: do not segfault when gathering stats from an uninitialized qht List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: QEMU Developers Cc: Changlong Xie , Richard Henderson , Peter Maydell 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 Signed-off-by: Emilio G. Cota --- 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