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Fix deadlock in galeramon

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The parameter extraction caused a recursive lock of the server
spinlock. To work around this, an unlocked version of server_get_parameter
is needed.

Ideally, a lock-free setup would be used but due to this being a bug fix,
it will have to be done later on.
This commit is contained in:
Markus Mäkelä 2018-05-11 09:00:54 +03:00
parent b776ed7821
commit 97eb7d2f9e
No known key found for this signature in database
GPG Key ID: 72D48FCE664F7B19
3 changed files with 28 additions and 15 deletions
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1
include/maxscale/server.h
View File

@ -358,6 +358,7 @@ extern void server_clear_status_nolock(SERVER *server, uint64_t bit);
extern void server_transfer_status(SERVER *dest_server, const SERVER *source_server);
extern void server_add_mon_user(SERVER *server, const char *user, const char *passwd);
extern size_t server_get_parameter(const SERVER *server, const char *name, char* out, size_t size);
extern size_t server_get_parameter_nolock(const SERVER *server, const char *name, char* out, size_t size);
extern void server_update_credentials(SERVER *server, const char *user, const char *passwd);
extern DCB* server_get_persistent(SERVER *server, const char *user, const char* ip, const char *protocol, int id);
extern void server_update_address(SERVER *server, const char *address);

32
server/core/server.cc
View File

@ -957,20 +957,15 @@ static void server_parameter_free(SERVER_PARAM *tofree)
}
/**
* Retrieve a parameter value from a server
* Same as server_get_parameter but doesn't lock the server
*
* @param server The server we are looking for a parameter of
* @param name The name of the parameter we require
* @param out Buffer where value is stored, use NULL to check if the parameter exists
* @param size Size of @c out, ignored if @c out is NULL
*
* @return Length of the parameter value or 0 if parameter was not found
* @note Should only be called when the server is already locked
*/
size_t server_get_parameter(const SERVER *server, const char *name, char* out, size_t size)
size_t server_get_parameter_nolock(const SERVER *server, const char *name, char* out, size_t size)
{
int len = 0;
ss_dassert(SPINLOCK_IS_LOCKED(server->lock));
size_t len = 0;
SERVER_PARAM *param = server->parameters;
spinlock_acquire(&server->lock);
while (param)
{
@ -982,6 +977,23 @@ size_t server_get_parameter(const SERVER *server, const char *name, char* out, s
param = param->next;
}
return len;
}
/**
* Retrieve a parameter value from a server
*
* @param server The server we are looking for a parameter of
* @param name The name of the parameter we require
* @param out Buffer where value is stored, use NULL to check if the parameter exists
* @param size Size of @c out, ignored if @c out is NULL
*
* @return Length of the parameter value or 0 if parameter was not found
*/
size_t server_get_parameter(const SERVER *server, const char *name, char* out, size_t size)
{
spinlock_acquire(&server->lock);
size_t len = server_get_parameter_nolock(server, name, out, size);
spinlock_release(&server->lock);
return len;
}

10
server/modules/monitor/galeramon/galeramon.c
View File

@ -695,7 +695,7 @@ static MXS_MONITORED_SERVER *get_candidate_master(MXS_MONITOR* mon)
moitor_servers->server->depth = 0;
char buf[50]; // Enough to hold most numbers
if (handle->use_priority && server_get_parameter(moitor_servers->server, "priority", buf, sizeof(buf)))
if (handle->use_priority && server_get_parameter_nolock(moitor_servers->server, "priority", buf, sizeof(buf)))
{
/** The server has a priority */
if ((currval = atoi(buf)) > 0)
@ -712,7 +712,7 @@ static MXS_MONITORED_SERVER *get_candidate_master(MXS_MONITOR* mon)
(!handle->use_priority || /** Server priority disabled*/
candidate_master == NULL || /** No candidate chosen */
/** Candidate has no priority */
!server_get_parameter(moitor_servers->server, "priority", buf, sizeof(buf))))
!server_get_parameter_nolock(moitor_servers->server, "priority", buf, sizeof(buf))))
{
if (min_id < 0 || moitor_servers->server->node_id < min_id)
{
@ -848,7 +848,7 @@ static void update_sst_donor_nodes(MXS_MONITOR *mon, int is_cluster)
*/
if (handle->use_priority &&
server_get_parameter(ptr->server, "priority", NULL, 0))
server_get_parameter_nolock(ptr->server, "priority", NULL, 0))
{
ignore_priority = false;
}
@ -983,8 +983,8 @@ static int compare_node_priority (const void *a, const void *b)
const MXS_MONITORED_SERVER *s_b = *(MXS_MONITORED_SERVER * const *)b;
char pri_a[50];
char pri_b[50];
bool have_a = server_get_parameter(s_a->server, "priority", pri_a, sizeof(pri_a));
bool have_b = server_get_parameter(s_b->server, "priority", pri_b, sizeof(pri_b));
bool have_a = server_get_parameter_nolock(s_a->server, "priority", pri_a, sizeof(pri_a));
bool have_b = server_get_parameter_nolock(s_b->server, "priority", pri_b, sizeof(pri_b));
/**
* Check priority parameter: