* David Goulet ([email protected]) wrote:
> Temporary fix the bug #7 issue for the 2.0 stable release. Refer to
> bugs.lttng.org for more information on the issues.
>
> The real stable fix is planned for 2.1+ stable release.
>
> Signed-off-by: David Goulet <[email protected]>
> ---
> src/bin/lttng-sessiond/ust-app.c | 36 +++++++++++++++++++++++++++++++++++-
> src/common/hashtable/hashtable.c | 2 --
> src/common/hashtable/hashtable.h | 2 ++
> 3 files changed, 37 insertions(+), 3 deletions(-)
>
> diff --git a/src/bin/lttng-sessiond/ust-app.c
> b/src/bin/lttng-sessiond/ust-app.c
> index 2b66b92..e82d38a 100644
> --- a/src/bin/lttng-sessiond/ust-app.c
> +++ b/src/bin/lttng-sessiond/ust-app.c
> @@ -29,6 +29,9 @@
>
> #include <common/common.h>
>
> +/* For add_unique_ust_app quick fix function for 2.0 stable release */
> +#include <common/hashtable/hashtable.h>
> +
> #include "ust-app.h"
> #include "ust-consumer.h"
> #include "ust-ctl.h"
> @@ -1257,6 +1260,31 @@ error:
> }
>
> /*
> + * TEMP function call to add uniquely a registered apps to a hash table.
> + *
> + * If a duplicate node is found when adding apps, we delete the old one and
> + * close the socket file descriptor as well. Must be inside a read side lock.
> + *
> + * Please refer to BUG #7 on bugs.lttng.org to understand the purpose and
> + * lifespan of this function.
> + */
> +static void add_unique_ust_app(struct lttng_ht *ht,
> + struct lttng_ht_node_ulong *node)
> +{
> + struct cds_lfht_node *node_ptr;
> + struct lttng_ht_node_ulong *old_node;
> +
> + node_ptr = cds_lfht_add_unique(ht->ht,
> + ht->hash_fct((void *) node->key, HASH_SEED),
> ht->match_fct,
> + (void *) node->key, &node->node);
> + if (node_ptr != &node->node) {
> + /* Double registration with same PID */
> + old_node = caa_container_of(node_ptr, struct
> lttng_ht_node_ulong, node);
> + call_rcu(&old_node->head, delete_ust_app_rcu);
ust_app_unregister():
/* Get the node reference for a call_rcu */
lttng_ht_lookup(ust_app_ht, (void *)((unsigned long) lta->key.pid),
&iter);
node = lttng_ht_iter_get_node_ulong(&iter);
if (node == NULL) {
ERR("Unable to find app sock %d by pid %d", sock, lta->key.pid);
goto error;
}
Should be allowed to not find the per pid entry without printing an
error. This will happen on the socket fd close that will follow this
removal.
> + }
Missing: lttng_ht_del() call before the call_rcu for delete_ust_app_rcu.
Missing: retry loop! After we cleared room for the new node we want to
add, we need to retry the add_unique.
Thanks,
Mathieu
> +}
> +
> +/*
> * Using pid and uid (of the app), allocate a new ust_app struct and
> * add it to the global traceable app list.
> *
> @@ -1307,7 +1335,13 @@ int ust_app_register(struct ust_register_msg *msg, int
> sock)
>
> rcu_read_lock();
> lttng_ht_add_unique_ulong(ust_app_sock_key_map, <a->key.node);
> - lttng_ht_add_unique_ulong(ust_app_ht, <a->node);
> + /*
> + * Changed for now. Refer to BUG #7 called "Double PID registering and
> + * unregistering race"
> + *
> + * lttng_ht_add_unique_ulong(ust_app_ht, <a->node);
> + */
> + add_unique_ust_app(ust_app_ht, <a->node);
> rcu_read_unlock();
>
> DBG("App registered with pid:%d ppid:%d uid:%d gid:%d sock:%d name:%s"
> diff --git a/src/common/hashtable/hashtable.c
> b/src/common/hashtable/hashtable.c
> index 2080107..83d4dfd 100644
> --- a/src/common/hashtable/hashtable.c
> +++ b/src/common/hashtable/hashtable.c
> @@ -27,8 +27,6 @@
> #include "hashtable.h"
> #include "utils.h"
>
> -#define HASH_SEED 0x42UL /* The answer to life */
> -
> static unsigned long min_hash_alloc_size = 1;
> static unsigned long max_hash_buckets_size = (1UL << 20);
>
> diff --git a/src/common/hashtable/hashtable.h
> b/src/common/hashtable/hashtable.h
> index 1c2889d..0f0339c 100644
> --- a/src/common/hashtable/hashtable.h
> +++ b/src/common/hashtable/hashtable.h
> @@ -23,6 +23,8 @@
> #include "rculfhash.h"
> #include "rculfhash-internal.h"
>
> +#define HASH_SEED 0x42UL /* The answer to life */
> +
> typedef unsigned long (*hash_fct)(void *_key, unsigned long seed);
> typedef cds_lfht_match_fct hash_match_fct;
>
> --
> 1.7.9
>
--
Mathieu Desnoyers
Operating System Efficiency R&D Consultant
EfficiOS Inc.
http://www.efficios.com
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