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fix: Make TLS initialization thread-safe and idempotent using pthread_once #11090

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fix: Make TLS initialization thread-safe and idempotent using pthread_once #11090

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6 changes: 5 additions & 1 deletion include/fluent-bit/flb_log.h
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Original file line number Diff line number Diff line change
Expand Up @@ -35,7 +35,11 @@
#include <stdarg.h>

/* FIXME: this extern should be auto-populated from flb_thread_storage.h */
extern FLB_TLS_DEFINE(struct flb_log, flb_log_ctx)
#ifndef FLB_HAVE_C_TLS
FLB_TLS_DECLARE(struct flb_log, flb_log_ctx);
#else
extern FLB_TLS_DEFINE(struct flb_log, flb_log_ctx);
#endif

/* Message types */
#define FLB_LOG_OFF 0
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4 changes: 4 additions & 0 deletions include/fluent-bit/flb_output.h
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Expand Up @@ -592,7 +592,11 @@ struct flb_out_flush_params {
struct flb_coro *coro; /* coroutine context */
};

#ifndef FLB_HAVE_C_TLS
FLB_TLS_DECLARE(struct flb_out_flush_params, out_flush_params);
#else
extern FLB_TLS_DEFINE(struct flb_out_flush_params, out_flush_params);
#endif

#define FLB_OUTPUT_RETURN(x) \
flb_output_return_do(x); \
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4 changes: 4 additions & 0 deletions include/fluent-bit/flb_scheduler.h
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Expand Up @@ -200,7 +200,11 @@ struct flb_sched_timer_coro_cb_params {
struct flb_coro *coro;
};

#ifndef FLB_HAVE_C_TLS
FLB_TLS_DECLARE(struct flb_sched_timer_coro_cb_params, sched_timer_coro_cb_params);
#else
extern FLB_TLS_DEFINE(struct flb_sched_timer_coro_cb_params, sched_timer_coro_cb_params);
#endif


struct flb_timer_cb_coro_params {
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34 changes: 31 additions & 3 deletions include/fluent-bit/flb_thread_storage.h
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Original file line number Diff line number Diff line change
Expand Up @@ -40,13 +40,41 @@
/* Fallback mode using pthread_*() for Thread-Local-Storage usage */
#define FLB_TLS_SET(key, val) pthread_setspecific(key, (void *) val)
#define FLB_TLS_GET(key) pthread_getspecific(key)
#define FLB_TLS_INIT(key) pthread_key_create(&key, NULL)
#define FLB_TLS_DEFINE(type, name) pthread_key_t name;

/*
* Thread-safe idempotent initialization using pthread_once.
* This ensures pthread_key_create is only called once even if FLB_TLS_INIT
* is called from multiple locations (different compilation units, hot reload, etc).
*/
#define FLB_TLS_INIT(key) \
do { \
extern pthread_once_t key##_once; \
void key##_init_func(void); \
pthread_once(&key##_once, key##_init_func); \
} while(0)

/* Define a TLS key with its pthread_once control and init function */
#define FLB_TLS_DEFINE(type, name) \
pthread_key_t name; \
pthread_once_t name##_once = PTHREAD_ONCE_INIT; \
void name##_init_func(void) { \
pthread_key_create(&name, NULL); \
}
Comment on lines +57 to +62
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⚠️ Potential issue | 🟠 Major

Handle pthread_key_create failure to avoid undefined TLS state.

With the new pthread_once wrapper we only invoke pthread_key_create() once. If that call returns an error (e.g. EAGAIN, ENOMEM), the key stays uninitialized but the pthread_once guard prevents any retry, so every later FLB_TLS_SET/GET will operate on an invalid key and the failure is silent. Before this change we at least retried on the next FLB_TLS_INIT, so this is a regression in resiliency. Please capture the return code, surface/log it, and keep the caller from proceeding (e.g. by storing the status in a companion variable that FLB_TLS_INIT checks and aborts or reports). That way we fail fast instead of running with a broken TLS slot.

🤖 Prompt for AI Agents 
In include/fluent-bit/flb_thread_storage.h around lines 57 to 62, the
pthread_key_create() result is ignored so if it fails the pthread_once guard
prevents retries and TLS key remains uninitialized; modify the macro to capture
the return code from pthread_key_create into a companion int status variable
(e.g. name##_init_rc), set it atomically, and have
FLB_TLS_INIT/FLB_TLS_GET/FLB_TLS_SET check that status and abort/log/return an
error when non-zero; also log the errno/rc when pthread_key_create fails to
surface the root cause and avoid proceeding with an invalid key.


/* Declare a TLS key that's defined elsewhere */
#define FLB_TLS_DECLARE(type, name) \
extern pthread_key_t name; \
extern pthread_once_t name##_once; \
void name##_init_func(void);
#endif


/* FIXME: this extern should be auto-populated from flb_thread_storage.h */
extern FLB_TLS_DEFINE(struct flb_worker, flb_worker_ctx)
#ifndef FLB_HAVE_C_TLS
FLB_TLS_DECLARE(struct flb_worker, flb_worker_ctx);
#else
extern FLB_TLS_DEFINE(struct flb_worker, flb_worker_ctx);
#endif


#endif /* !FLB_THREAD_STORAGE_H */
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