The deadlock was found using this backtrace
Thread 5:
0 __lll_lock_wait () at ../sysdeps/unix/sysv/linux/x86_64/lowlevellock.S:135
1 0x00007efc6b650023 in __GI___pthread_mutex_lock
(mutex=mutex@entry=0x55fc37128400 <worker_lock>) at
../nptl/pthread_mutex_lock.c:78
2 0x000055fc36efbe05 in run_as_destroy_worker () at runas.c:1233
3 0x000055fc36efc2e7 in run_as_restart_worker (worker=<optimized out>) at
runas.c:998
4 run_as (cmd=cmd@entry=RUN_AS_UNLINK, data=data@entry=0x7efc5b7fa630,
ret_value=ret_value@entry=0x7efc5b7fa510, uid=uid@entry=1000,
gid=gid@entry=1000) at runas.c:1033
5 0x000055fc36efc9ce in run_as_unlink (path=path@entry=0x7efc5b7fb690
"/home/joraj/lttng-traces/auto-20190116-111518/20190116T111729-0500-33/kernel/index/channel0_3.idx",
uid=uid@entry=1000, gid=gid@entry=1000) at runas.c :1120
6 0x000055fc36ef7feb in utils_unlink_stream_file
(path_name=path_name@entry=0x7efc5b7fc7e0
"/home/joraj/lttng-traces/auto-20190116-111518/20190116T111729-0500-33/kernel/index",
file_name=file_name@entry=0x7efc500085d4 "channel0_3", size=size@entry=0,
count=count@entry=0, uid=uid@entry=1000, gid=gid@entry=1000,
suffix=0x55fc36f19b26 ".idx") at utils.c:929
7 0x000055fc36f01d4e in lttng_index_file_create
(path_name=path_name@entry=0x7efc500087a0
"/home/joraj/lttng-traces/auto-20190116-111518/20190116T111729-0500-33/kernel",
stream_name=stream_name@entry=0x7efc500085d4 "channel0_3", uid=1000, gid=1000,
size=0, count=0, major=1, minor=1) at index.c:79
8 0x000055fc36ed9475 in rotate_local_stream (ctx=<optimized out>,
stream=0x7efc50008460) at consumer.c:4105
9 0x000055fc36ed98b5 in lttng_consumer_rotate_stream
(ctx=ctx@entry=0x55fc37428d80, stream=stream@entry=0x7efc50008460,
rotated=rotated@entry=0x7efc5b7fdb27) at consumer.c:4181
10 0x000055fc36ee354e in lttng_kconsumer_read_subbuffer
(stream=stream@entry=0x7efc50008460, ctx=ctx@entry=0x55fc37428d80,
rotated=rotated@entry=0x7efc5b7fdb27) at kernel-consumer.c:1740
11 0x000055fc36ed7a30 in lttng_consumer_read_subbuffer (stream=0x7efc50008460,
ctx=0x55fc37428d80) at consumer.c:3383
12 0x000055fc36ed4b74 in consumer_thread_data_poll (data=0x55fc37428d80) at
consumer.c:2751
13 0x00007efc6b64d6db in start_thread (arg=0x7efc5b7fe700) at
pthread_create.c:463
14 0x00007efc6af6488f in clone () at
../sysdeps/unix/sysv/linux/x86_64/clone.S:95
The owner of the lock is itself:
print worker_lock.__data.__owner
$2 = 25725
thread find 25725
Thread 5 has target id 'Thread 0x7efc5b7fe700 (LWP 25725)'
The worker_lock is first taken in frame #4: run_as runas.c:1033
pthread_mutex_lock(&worker_lock);
if (use_clone()) {
...
/*
* If the worker thread crashed the errno is set to EIO. we log
* the error and start a new worker process.
*/
if (ret == -1 && saved_errno == EIO) {
DBG("Socket closed unexpectedly... "
"Restarting the worker process");
-> ret = run_as_restart_worker(global_worker);
if (ret == -1) {
ERR("Failed to restart worker process.");
goto err;
}
Solution
========
Create run_as_restart_worker_no_lock which does not to take the lock on
execution.
Use run_as_restart_worker_no_lock at the run_as error path call site.
Use run_as_restart_worker_no_lock inside run_as_restart_worker while
holding the worker lock to provide identical behaviour to other call sites.
Signed-off-by: Jonathan Rajotte <jonathan.rajotte-jul...@efficios.com>
---
src/common/runas.c | 89 ++++++++++++++++++++++++----------------------
1 file changed, 47 insertions(+), 42 deletions(-)
diff --git a/src/common/runas.c b/src/common/runas.c
index d727cf417..9e6277078 100644
--- a/src/common/runas.c
+++ b/src/common/runas.c
@@ -986,6 +986,51 @@ error_procname_alloc:
return ret;
}
+static
+void run_as_destroy_worker_no_lock(void)
+{
+ struct run_as_worker *worker = global_worker;
+
+ DBG("Destroying run_as worker");
+ if (!worker) {
+ return;
+ }
+ /* Close unix socket */
+ DBG("Closing run_as worker socket");
+ if (lttcomm_close_unix_sock(worker->sockpair[0])) {
+ PERROR("close");
+ }
+ worker->sockpair[0] = -1;
+ /* Wait for worker. */
+ for (;;) {
+ int status;
+ pid_t wait_ret;
+
+ wait_ret = waitpid(worker->pid, &status, 0);
+ if (wait_ret < 0) {
+ if (errno == EINTR) {
+ continue;
+ }
+ PERROR("waitpid");
+ break;
+ }
+
+ if (WIFEXITED(status)) {
+ LOG(WEXITSTATUS(status) == 0 ? PRINT_DBG : PRINT_ERR,
+ DEFAULT_RUN_AS_WORKER_NAME " terminated
with status code %d",
+ WEXITSTATUS(status));
+ break;
+ } else if (WIFSIGNALED(status)) {
+ ERR(DEFAULT_RUN_AS_WORKER_NAME " was killed by signal
%d",
+ WTERMSIG(status));
+ break;
+ }
+ }
+ free(worker->procname);
+ free(worker);
+ global_worker = NULL;
+}
+
static
int run_as_restart_worker(struct run_as_worker *worker)
{
@@ -995,7 +1040,7 @@ int run_as_restart_worker(struct run_as_worker *worker)
procname = worker->procname;
/* Close socket to run_as worker process and clean up the zombie
process */
- run_as_destroy_worker();
+ run_as_destroy_worker_no_lock();
/* Create a new run_as worker process*/
ret = run_as_create_worker_no_lock(procname);
@@ -1227,47 +1272,7 @@ int run_as_create_worker(const char *procname)
LTTNG_HIDDEN
void run_as_destroy_worker(void)
{
- struct run_as_worker *worker = global_worker;
-
- DBG("Destroying run_as worker");
pthread_mutex_lock(&worker_lock);
- if (!worker) {
- goto end;
- }
- /* Close unix socket */
- DBG("Closing run_as worker socket");
- if (lttcomm_close_unix_sock(worker->sockpair[0])) {
- PERROR("close");
- }
- worker->sockpair[0] = -1;
- /* Wait for worker. */
- for (;;) {
- int status;
- pid_t wait_ret;
-
- wait_ret = waitpid(worker->pid, &status, 0);
- if (wait_ret < 0) {
- if (errno == EINTR) {
- continue;
- }
- PERROR("waitpid");
- break;
- }
-
- if (WIFEXITED(status)) {
- LOG(WEXITSTATUS(status) == 0 ? PRINT_DBG : PRINT_ERR,
- DEFAULT_RUN_AS_WORKER_NAME " terminated
with status code %d",
- WEXITSTATUS(status));
- break;
- } else if (WIFSIGNALED(status)) {
- ERR(DEFAULT_RUN_AS_WORKER_NAME " was killed by signal
%d",
- WTERMSIG(status));
- break;
- }
- }
- free(worker->procname);
- free(worker);
- global_worker = NULL;
-end:
+ run_as_destroy_worker_no_lock();
pthread_mutex_unlock(&worker_lock);
}
--
2.17.1
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