Commit 7266ae91 authored by Emilio G. Cota's avatar Emilio G. Cota Committed by Paolo Bonzini
Browse files

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



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: default avatarEmilio 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: default avatarPaolo Bonzini <pbonzini@redhat.com>
parent 767db021

tests/test-qht.c

+4 −0
Original line number Diff line number Diff line
@@ -95,8 +95,12 @@ 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);

translate-all.c

+39 −31
Original line number Diff line number Diff line
@@ -1663,15 +1663,50 @@ void tb_flush_jmp_cache(CPUState *cpu, target_ulong addr) 
           TB_JMP_PAGE_SIZE * sizeof(TranslationBlock *));

}



static void print_qht_statistics(FILE *f, fprintf_function cpu_fprintf,

                                 struct qht_stats hst)

{

    uint32_t hgram_opts;

    size_t hgram_bins;

    char *hgram;



    if (!hst.head_buckets) {

        return;

    }

    cpu_fprintf(f, "TB hash buckets     %zu/%zu (%0.2f%% head buckets used)\n",

                hst.used_head_buckets, hst.head_buckets,

                (double)hst.used_head_buckets / hst.head_buckets * 100);



    hgram_opts =  QDIST_PR_BORDER | QDIST_PR_LABELS;

    hgram_opts |= QDIST_PR_100X   | QDIST_PR_PERCENT;

    if (qdist_xmax(&hst.occupancy) - qdist_xmin(&hst.occupancy) == 1) {

        hgram_opts |= QDIST_PR_NODECIMAL;

    }

    hgram = qdist_pr(&hst.occupancy, 10, hgram_opts);

    cpu_fprintf(f, "TB hash occupancy   %0.2f%% avg chain occ. Histogram: %s\n",

                qdist_avg(&hst.occupancy) * 100, hgram);

    g_free(hgram);



    hgram_opts = QDIST_PR_BORDER | QDIST_PR_LABELS;

    hgram_bins = qdist_xmax(&hst.chain) - qdist_xmin(&hst.chain);

    if (hgram_bins > 10) {

        hgram_bins = 10;

    } else {

        hgram_bins = 0;

        hgram_opts |= QDIST_PR_NODECIMAL | QDIST_PR_NOBINRANGE;

    }

    hgram = qdist_pr(&hst.chain, hgram_bins, hgram_opts);

    cpu_fprintf(f, "TB hash avg chain   %0.3f buckets. Histogram: %s\n",

                qdist_avg(&hst.chain), hgram);

    g_free(hgram);

}



void dump_exec_info(FILE *f, fprintf_function cpu_fprintf)

{

    int i, target_code_size, max_target_code_size;

    int direct_jmp_count, direct_jmp2_count, cross_page;

    TranslationBlock *tb;

    struct qht_stats hst;

    uint32_t hgram_opts;

    size_t hgram_bins;

    char *hgram;



    target_code_size = 0;

    max_target_code_size = 0;
@@ -1724,34 +1759,7 @@ void dump_exec_info(FILE *f, fprintf_function cpu_fprintf) 
                        tcg_ctx.tb_ctx.nb_tbs : 0);



    qht_statistics_init(&tcg_ctx.tb_ctx.htable, &hst);



    cpu_fprintf(f, "TB hash buckets     %zu/%zu (%0.2f%% head buckets used)\n",

                hst.used_head_buckets, hst.head_buckets,

                (double)hst.used_head_buckets / hst.head_buckets * 100);



    hgram_opts =  QDIST_PR_BORDER | QDIST_PR_LABELS;

    hgram_opts |= QDIST_PR_100X   | QDIST_PR_PERCENT;

    if (qdist_xmax(&hst.occupancy) - qdist_xmin(&hst.occupancy) == 1) {

        hgram_opts |= QDIST_PR_NODECIMAL;

    }

    hgram = qdist_pr(&hst.occupancy, 10, hgram_opts);

    cpu_fprintf(f, "TB hash occupancy   %0.2f%% avg chain occ. Histogram: %s\n",

                qdist_avg(&hst.occupancy) * 100, hgram);

    g_free(hgram);



    hgram_opts = QDIST_PR_BORDER | QDIST_PR_LABELS;

    hgram_bins = qdist_xmax(&hst.chain) - qdist_xmin(&hst.chain);

    if (hgram_bins > 10) {

        hgram_bins = 10;

    } else {

        hgram_bins = 0;

        hgram_opts |= QDIST_PR_NODECIMAL | QDIST_PR_NOBINRANGE;

    }

    hgram = qdist_pr(&hst.chain, hgram_bins, hgram_opts);

    cpu_fprintf(f, "TB hash avg chain   %0.3f buckets. Histogram: %s\n",

                qdist_avg(&hst.chain), hgram);

    g_free(hgram);



    print_qht_statistics(f, cpu_fprintf, hst);

    qht_statistics_destroy(&hst);



    cpu_fprintf(f, "\nStatistics:\n");

util/qht.c

+6 −1
Original line number Diff line number Diff line
@@ -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];