6.15-stable review patch. If anyone has any objections, please let me know.
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From: Steven Rostedt rostedt@goodmis.org
[ Upstream commit 3aceaa539cfe3a2e62bd92e6697d9fae1c20c0be ]
Freeing of filters requires to wait for both an RCU grace period as well as a RCU task trace wait period after they have been detached from their lists. The trace task period can be quite large so the freeing of the filters was moved to use the call_rcu*() routines. The problem with that is that the callback functions of call_rcu*() is done from a soft irq and can cause latencies if the callback takes a bit of time.
The filters are freed per event in a system and the syscalls system contains an event per system call, which can be over 700 events. Freeing 700 filters in a bottom half is undesirable.
Instead, move the freeing to use queue_rcu_work() which is done in task context.
Link: https://lore.kernel.org/all/9a2f0cd0-1561-4206-8966-f93ccd25927f@paulmck-lap...
Cc: Masami Hiramatsu mhiramat@kernel.org Cc: Mathieu Desnoyers mathieu.desnoyers@efficios.com Link: https://lore.kernel.org/20250609131732.04fd303b@gandalf.local.home Fixes: a9d0aab5eb33 ("tracing: Fix regression of filter waiting a long time on RCU synchronization") Suggested-by: "Paul E. McKenney" paulmck@kernel.org Reviewed-by: Paul E. McKenney paulmck@kernel.org Signed-off-by: Steven Rostedt (Google) rostedt@goodmis.org Signed-off-by: Sasha Levin sashal@kernel.org --- kernel/trace/trace_events_filter.c | 28 ++++++++++++++++++++-------- 1 file changed, 20 insertions(+), 8 deletions(-)
diff --git a/kernel/trace/trace_events_filter.c b/kernel/trace/trace_events_filter.c index cca676f651b1..8fc5323a2ed3 100644 --- a/kernel/trace/trace_events_filter.c +++ b/kernel/trace/trace_events_filter.c @@ -1342,13 +1342,14 @@ struct filter_list {
struct filter_head { struct list_head list; - struct rcu_head rcu; + union { + struct rcu_head rcu; + struct rcu_work rwork; + }; };
- -static void free_filter_list(struct rcu_head *rhp) +static void free_filter_list(struct filter_head *filter_list) { - struct filter_head *filter_list = container_of(rhp, struct filter_head, rcu); struct filter_list *filter_item, *tmp;
list_for_each_entry_safe(filter_item, tmp, &filter_list->list, list) { @@ -1359,9 +1360,20 @@ static void free_filter_list(struct rcu_head *rhp) kfree(filter_list); }
+static void free_filter_list_work(struct work_struct *work) +{ + struct filter_head *filter_list; + + filter_list = container_of(to_rcu_work(work), struct filter_head, rwork); + free_filter_list(filter_list); +} + static void free_filter_list_tasks(struct rcu_head *rhp) { - call_rcu(rhp, free_filter_list); + struct filter_head *filter_list = container_of(rhp, struct filter_head, rcu); + + INIT_RCU_WORK(&filter_list->rwork, free_filter_list_work); + queue_rcu_work(system_wq, &filter_list->rwork); }
/* @@ -1458,7 +1470,7 @@ static void filter_free_subsystem_filters(struct trace_subsystem_dir *dir, tracepoint_synchronize_unregister();
if (head) - free_filter_list(&head->rcu); + free_filter_list(head);
list_for_each_entry(file, &tr->events, list) { if (file->system != dir || !file->filter) @@ -2303,7 +2315,7 @@ static int process_system_preds(struct trace_subsystem_dir *dir, return 0; fail: /* No call succeeded */ - free_filter_list(&filter_list->rcu); + free_filter_list(filter_list); parse_error(pe, FILT_ERR_BAD_SUBSYS_FILTER, 0); return -EINVAL; fail_mem: @@ -2313,7 +2325,7 @@ static int process_system_preds(struct trace_subsystem_dir *dir, if (!fail) delay_free_filter(filter_list); else - free_filter_list(&filter_list->rcu); + free_filter_list(filter_list);
return -ENOMEM; }