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SubjectRe: [PATCH RFC 06/10] perf tools: lock to protect comm_str rb tree
Em Thu, Sep 07, 2017 at 10:55:50AM -0700, kan.liang@intel.com escreveu:
> From: Kan Liang <kan.liang@intel.com>
>
> Add comm_str_lock to protect comm_str rb tree.
>
> Signed-off-by: Kan Liang <kan.liang@intel.com>
> ---
> tools/perf/util/comm.c | 18 ++++++++++++++----
> 1 file changed, 14 insertions(+), 4 deletions(-)
>
> diff --git a/tools/perf/util/comm.c b/tools/perf/util/comm.c
> index 7bc981b..1bdfef1 100644
> --- a/tools/perf/util/comm.c
> +++ b/tools/perf/util/comm.c
> @@ -5,6 +5,7 @@
> #include <stdio.h>
> #include <string.h>
> #include <linux/refcount.h>
> +#include <pthread.h>
>
> struct comm_str {
> char *str;
> @@ -14,6 +15,7 @@ struct comm_str {
>
> /* Should perhaps be moved to struct machine */
> static struct rb_root comm_str_root;
> +static pthread_mutex_t comm_str_lock = PTHREAD_MUTEX_INITIALIZER;
>
> static struct comm_str *comm_str__get(struct comm_str *cs)
> {
> @@ -24,11 +26,13 @@ static struct comm_str *comm_str__get(struct comm_str *cs)
>
> static void comm_str__put(struct comm_str *cs)
> {
> + pthread_mutex_lock(&comm_str_lock);
> if (cs && refcount_dec_and_test(&cs->refcnt)) {
> rb_erase(&cs->rb_node, &comm_str_root);
> zfree(&cs->str);
> free(cs);
> }
> + pthread_mutex_unlock(&comm_str_lock);
> }

The above should use a smaller locked section, i.e.:

static void comm_str__put(struct comm_str *cs)
{
if (cs && refcount_dec_and_test(&cs->refcnt)) {
+ pthread_mutex_lock(&comm_str_lock);
rb_erase(&cs->rb_node, &comm_str_root);
+ pthread_mutex_unlock(&comm_str_lock);
zfree(&cs->str);
free(cs);
}
}

> static struct comm_str *comm_str__alloc(const char *str)
> @@ -52,18 +56,22 @@ static struct comm_str *comm_str__alloc(const char *str)
>
> static struct comm_str *comm_str__findnew(const char *str, struct rb_root *root)

The usual way is to just rename the above to __comm_str__findnew(),
leaving it unlocked, and then add a locked wrapper:

static struct comm_str *comm_str__findnew(const char *str, struct rb_root *root)
{
struct comm_str *cs;
pthread_mutex_lock(&comm_str_lock);
cs = __comm_str__findnew(str, root);
pthread_mutex_unlock(&comm_str_lock);
return cs;
}

> {
> - struct rb_node **p = &root->rb_node;
> struct rb_node *parent = NULL;
> struct comm_str *iter, *new;
> + struct rb_node **p;
> int cmp;
>
> + pthread_mutex_lock(&comm_str_lock);
> + p = &root->rb_node;
> while (*p != NULL) {
> parent = *p;
> iter = rb_entry(parent, struct comm_str, rb_node);
>
> cmp = strcmp(str, iter->str);
> - if (!cmp)
> - return comm_str__get(iter);
> + if (!cmp) {
> + new = comm_str__get(iter);
> + goto unlock;
> + }
>
> if (cmp < 0)
> p = &(*p)->rb_left;
> @@ -73,11 +81,13 @@ static struct comm_str *comm_str__findnew(const char *str, struct rb_root *root)
>
> new = comm_str__alloc(str);
> if (!new)
> - return NULL;
> + goto unlock;
>
> rb_link_node(&new->rb_node, parent, p);
> rb_insert_color(&new->rb_node, root);
>
> +unlock:
> + pthread_mutex_unlock(&comm_str_lock);
> return new;
> }
>
> --
> 2.5.5

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