diff options
| -rw-r--r-- | kernel/tracepoint.c | 155 |
1 files changed, 135 insertions, 20 deletions
diff --git a/kernel/tracepoint.c b/kernel/tracepoint.c index fc32821f8240..efd14c79fab4 100644 --- a/kernel/tracepoint.c +++ b/kernel/tracepoint.c @@ -15,12 +15,57 @@ #include <linux/sched/task.h> #include <linux/static_key.h> +enum tp_func_state { + TP_FUNC_0, + TP_FUNC_1, + TP_FUNC_2, + TP_FUNC_N, +}; + extern tracepoint_ptr_t __start___tracepoints_ptrs[]; extern tracepoint_ptr_t __stop___tracepoints_ptrs[]; DEFINE_SRCU(tracepoint_srcu); EXPORT_SYMBOL_GPL(tracepoint_srcu); +enum tp_transition_sync { + TP_TRANSITION_SYNC_1_0_1, + TP_TRANSITION_SYNC_N_2_1, + + _NR_TP_TRANSITION_SYNC, +}; + +struct tp_transition_snapshot { + unsigned long rcu; + unsigned long srcu; + bool ongoing; +}; + +/* Protected by tracepoints_mutex */ +static struct tp_transition_snapshot tp_transition_snapshot[_NR_TP_TRANSITION_SYNC]; + +static void tp_rcu_get_state(enum tp_transition_sync sync) +{ + struct tp_transition_snapshot *snapshot = &tp_transition_snapshot[sync]; + + /* Keep the latest get_state snapshot. */ + snapshot->rcu = get_state_synchronize_rcu(); + snapshot->srcu = start_poll_synchronize_srcu(&tracepoint_srcu); + snapshot->ongoing = true; +} + +static void tp_rcu_cond_sync(enum tp_transition_sync sync) +{ + struct tp_transition_snapshot *snapshot = &tp_transition_snapshot[sync]; + + if (!snapshot->ongoing) + return; + cond_synchronize_rcu(snapshot->rcu); + if (!poll_state_synchronize_srcu(&tracepoint_srcu, snapshot->srcu)) + synchronize_srcu(&tracepoint_srcu); + snapshot->ongoing = false; +} + /* Set to 1 to enable tracepoint debug output */ static const int tracepoint_debug; @@ -246,26 +291,29 @@ static void *func_remove(struct tracepoint_func **funcs, return old; } -static void tracepoint_update_call(struct tracepoint *tp, struct tracepoint_func *tp_funcs, bool sync) +/* + * Count the number of functions (enum tp_func_state) in a tp_funcs array. + */ +static enum tp_func_state nr_func_state(const struct tracepoint_func *tp_funcs) +{ + if (!tp_funcs) + return TP_FUNC_0; + if (!tp_funcs[1].func) + return TP_FUNC_1; + if (!tp_funcs[2].func) + return TP_FUNC_2; + return TP_FUNC_N; /* 3 or more */ +} + +static void tracepoint_update_call(struct tracepoint *tp, struct tracepoint_func *tp_funcs) { void *func = tp->iterator; /* Synthetic events do not have static call sites */ if (!tp->static_call_key) return; - - if (!tp_funcs[1].func) { + if (nr_func_state(tp_funcs) == TP_FUNC_1) func = tp_funcs[0].func; - /* - * If going from the iterator back to a single caller, - * we need to synchronize with __DO_TRACE to make sure - * that the data passed to the callback is the one that - * belongs to that callback. - */ - if (sync) - tracepoint_synchronize_unregister(); - } - __static_call_update(tp->static_call_key, tp->static_call_tramp, func); } @@ -299,9 +347,41 @@ static int tracepoint_add_func(struct tracepoint *tp, * a pointer to it. This array is referenced by __DO_TRACE from * include/linux/tracepoint.h using rcu_dereference_sched(). */ - tracepoint_update_call(tp, tp_funcs, false); - rcu_assign_pointer(tp->funcs, tp_funcs); - static_key_enable(&tp->key); + switch (nr_func_state(tp_funcs)) { + case TP_FUNC_1: /* 0->1 */ + /* + * Make sure new static func never uses old data after a + * 1->0->1 transition sequence. + */ + tp_rcu_cond_sync(TP_TRANSITION_SYNC_1_0_1); + /* Set static call to first function */ + tracepoint_update_call(tp, tp_funcs); + /* Both iterator and static call handle NULL tp->funcs */ + rcu_assign_pointer(tp->funcs, tp_funcs); + static_key_enable(&tp->key); + break; + case TP_FUNC_2: /* 1->2 */ + /* Set iterator static call */ + tracepoint_update_call(tp, tp_funcs); + /* + * Iterator callback installed before updating tp->funcs. + * Requires ordering between RCU assign/dereference and + * static call update/call. + */ + fallthrough; + case TP_FUNC_N: /* N->N+1 (N>1) */ + rcu_assign_pointer(tp->funcs, tp_funcs); + /* + * Make sure static func never uses incorrect data after a + * N->...->2->1 (N>1) transition sequence. + */ + if (tp_funcs[0].data != old[0].data) + tp_rcu_get_state(TP_TRANSITION_SYNC_N_2_1); + break; + default: + WARN_ON_ONCE(1); + break; + } release_probes(old); return 0; @@ -328,17 +408,52 @@ static int tracepoint_remove_func(struct tracepoint *tp, /* Failed allocating new tp_funcs, replaced func with stub */ return 0; - if (!tp_funcs) { + switch (nr_func_state(tp_funcs)) { + case TP_FUNC_0: /* 1->0 */ /* Removed last function */ if (tp->unregfunc && static_key_enabled(&tp->key)) tp->unregfunc(); static_key_disable(&tp->key); + /* Set iterator static call */ + tracepoint_update_call(tp, tp_funcs); + /* Both iterator and static call handle NULL tp->funcs */ + rcu_assign_pointer(tp->funcs, NULL); + /* + * Make sure new static func never uses old data after a + * 1->0->1 transition sequence. + */ + tp_rcu_get_state(TP_TRANSITION_SYNC_1_0_1); + break; + case TP_FUNC_1: /* 2->1 */ rcu_assign_pointer(tp->funcs, tp_funcs); - } else { + /* + * Make sure static func never uses incorrect data after a + * N->...->2->1 (N>2) transition sequence. If the first + * element's data has changed, then force the synchronization + * to prevent current readers that have loaded the old data + * from calling the new function. + */ + if (tp_funcs[0].data != old[0].data) + tp_rcu_get_state(TP_TRANSITION_SYNC_N_2_1); + tp_rcu_cond_sync(TP_TRANSITION_SYNC_N_2_1); + /* Set static call to first function */ + tracepoint_update_call(tp, tp_funcs); + break; + case TP_FUNC_2: /* N->N-1 (N>2) */ + fallthrough; + case TP_FUNC_N: rcu_assign_pointer(tp->funcs, tp_funcs); - tracepoint_update_call(tp, tp_funcs, - tp_funcs[0].func != old[0].func); + /* + * Make sure static func never uses incorrect data after a + * N->...->2->1 (N>2) transition sequence. + */ + if (tp_funcs[0].data != old[0].data) + tp_rcu_get_state(TP_TRANSITION_SYNC_N_2_1); + break; + default: + WARN_ON_ONCE(1); + break; } release_probes(old); return 0; |