diff options
Diffstat (limited to 'src')
| -rw-r--r-- | src/fsm.c | 56 |
1 files changed, 47 insertions, 9 deletions
@@ -102,8 +102,20 @@ static __thread struct { unsigned int depth; /*! Talloc context to collect all deferred deallocations (FSM instances, and talloc objects if any). */ void *collect_ctx; + /*! See osmo_fsm_set_dealloc_ctx() */ + void *fsm_dealloc_ctx; } fsm_term_safely; +/*! Internal call to free an FSM instance, which redirects to the context set by osmo_fsm_set_dealloc_ctx() if any. + */ +static void fsm_free_or_steal(void *talloc_object) +{ + if (fsm_term_safely.fsm_dealloc_ctx) + talloc_steal(fsm_term_safely.fsm_dealloc_ctx, talloc_object); + else + talloc_free(talloc_object); +} + /*! specify if FSM instance addresses should be logged or not * * By default, the FSM name includes the pointer address of the \ref @@ -139,11 +151,9 @@ void osmo_fsm_log_timeouts(bool log_timeouts) /*! Enable safer way to deallocate cascades of terminating FSM instances. * - * For legacy compatibility, this is disabled by default. In newer programs / releases, it is recommended to enable this - * feature during main() startup, since it greatly simplifies deallocating child, parent and other FSM instances without - * running into double-free or use-after-free scenarios. When enabled, this feature changes the order of logging, which - * may break legacy unit test expectations, and changes the order of deallocation to after the parent term event is - * dispatched. + * Note, using osmo_fsm_set_dealloc_ctx() is a more general solution to this same problem. + * Particularly, in a program using osmo_select_main_ctx(), the simplest solution to avoid most use-after-free problems + * from FSM instance deallocation is using osmo_fsm_set_dealloc_ctx(OTC_SELECT). * * When enabled, an FSM instance termination detects whether another FSM instance is already terminating, and instead of * deallocating immediately, collects all terminating FSM instances in a talloc context, to be bulk deallocated once all @@ -155,6 +165,9 @@ void osmo_fsm_log_timeouts(bool log_timeouts) * * For illustration, see fsm_dealloc_test.c. * + * When enabled, this feature changes the order of logging, which may break legacy unit test expectations, and changes + * the order of deallocation to after the parent term event is dispatched. + * * \param[in] term_safely Pass true to switch to safer FSM instance termination behavior. */ void osmo_fsm_term_safely(bool term_safely) @@ -162,6 +175,31 @@ void osmo_fsm_term_safely(bool term_safely) fsm_term_safely_enabled = term_safely; } +/*! Instead of deallocating FSM instances, move them to the given talloc context. + * + * It is the caller's responsibility to clear this context to actually free the memory of terminated FSM instances. + * Make sure to not talloc_free(ctx) itself before setting a different osmo_fsm_set_dealloc_ctx(). To clear a ctx + * without the need to call osmo_fsm_set_dealloc_ctx() again, rather use talloc_free_children(ctx). + * + * For example, to defer deallocation to the next osmo_select_main_ctx() iteration, set this to OTC_SELECT. + * + * Deferring deallocation is the simplest solution to avoid most use-after-free problems from FSM instance deallocation. + * This is a simpler and more general solution than osmo_fsm_term_safely(). + * + * To disable the feature again, pass NULL as ctx. + * + * Both osmo_fsm_term_safely() and osmo_fsm_set_dealloc_ctx() can be enabled at the same time, which will result in + * first collecting deallocated FSM instances in fsm_term_safely.collect_ctx, and finally reparenting that to the ctx + * passed here. However, in practice, it does not really make sense to enable both at the same time. + * + * \param ctx[in] Instead of talloc_free()int, talloc_steal() all future deallocated osmo_fsm_inst instances to this + * ctx. If NULL, go back to talloc_free() as usual. + */ +void osmo_fsm_set_dealloc_ctx(void *ctx) +{ + fsm_term_safely.fsm_dealloc_ctx = ctx; +} + /*! talloc_free() the given object immediately, or once ongoing FSM terminations are done. * * If an FSM deallocation cascade is ongoing, talloc_steal() the given talloc_object into the talloc context that is @@ -185,7 +223,7 @@ void osmo_fsm_term_safely(bool term_safely) static void osmo_fsm_defer_free(void *talloc_object) { if (!fsm_term_safely.depth) { - talloc_free(talloc_object); + fsm_free_or_steal(talloc_object); return; } @@ -412,7 +450,7 @@ struct osmo_fsm_inst *osmo_fsm_inst_alloc(struct osmo_fsm *fsm, void *ctx, void osmo_timer_setup(&fi->timer, fsm_tmr_cb, fi); if (osmo_fsm_inst_update_id(fi, id) < 0) { - talloc_free(fi); + fsm_free_or_steal(fi); return NULL; } @@ -529,11 +567,11 @@ void osmo_fsm_inst_free(struct osmo_fsm_inst *fi) * deallocate separately to avoid use-after-free errors, put it in there and deallocate all at once. */ LOGPFSM(fi, "Deallocated, including all deferred deallocations\n"); osmo_fsm_defer_free(fi); - talloc_free(fsm_term_safely.collect_ctx); + fsm_free_or_steal(fsm_term_safely.collect_ctx); fsm_term_safely.collect_ctx = NULL; } else { LOGPFSM(fi, "Deallocated\n"); - talloc_free(fi); + fsm_free_or_steal(fi); } fsm_term_safely.root_fi = NULL; } |