tracing: Fixes for 6.16
Subsystems (3)
Steven Rostedt
maintainercover tracing: Fixes for 6.16
[ Resending as my scripts messed up the first patch email addresses
and the sending crashed ]
tracing fixes:
- Fix regression of waiting a long time on updating trace event filters
When the faultable trace points were added, it needed task trace RCU synchronization. This was added to the tracepoint_synchronize_unregister() function. The filter logic always called this function whenever it updated the trace event filters before freeing the old filters. This increased the time of "trace-cmd record" from taking 13 seconds to running over 2 minutes to complete.
Move the freeing of the filters to call_rcu*() logic, which brings the time back down to 13 seconds.
- Fix ring_buffer_subbuf_order_set() error path lock protection
The error path of the ring_buffer_subbuf_order_set() released the mutex too early and allowed subsequent accesses to setting the subbuffer size to corrupt the data and cause a bug.
By moving the mutex locking to the end of the error path, it prevents the reentrant access to the critical data and also allows the function to convert the taking of the mutex over to the guard() logic.
- Remove unused power management clock events
The clock events were added in 2010 for power management. In 2011 arm used them. In 2013 the code they were used in was removed. These events have been wasting memory since then.
git://git.kernel.org/pub/scm/linux/kernel/git/trace/linux-trace.git
trace/fixes
Head SHA1: 28e6aecb1a79e178d870aee0b71f97cca669fd9b
Dmitry Antipov (1):
ring-buffer: Fix buffer locking in ring_buffer_subbuf_order_set()
Steven Rostedt (2):
tracing: Fix regression of filter waiting a long time on RCU synchronization
tracing: PM: Remove unused clock events
----
include/trace/events/power.h | 47 ----------- kernel/trace/ring_buffer.c | 4 +- kernel/trace/trace_events_filter.c | 164 ++++++++++++++++++++++++++++--------- 3 files changed, 128 insertions(+), 87 deletions(-)
Steven Rostedt
maintainerPATCH 1/3 tracing: Fix regression of filter waiting a long time on RCU synchronization
From: Steven Rostedt <[email protected]>
When faultable trace events were added, a trace event may no longer use normal RCU to synchronize but instead used synchronize_rcu_tasks_trace(). This synchronization takes a much longer time to synchronize.
The filter logic would free the filters by calling tracepoint_synchronize_unregister() after it unhooked the filter strings and before freeing them. With this function now calling synchronize_rcu_tasks_trace() this increased the time to free a filter tremendously. On a PREEMPT_RT system, it was even more noticeable.
# time trace-cmd record -p function sleep 1 [..] real 2m29.052s user 0m0.244s sys 0m20.136s
As trace-cmd would clear out all the filters before recording, it could take up to 2 minutes to do a recording of "sleep 1".
To find out where the issues was:
~# trace-cmd sqlhist -e -n sched_stack select start.prev_state as state, end.next_comm as comm, TIMESTAMP_DELTA_USECS as delta, start.STACKTRACE as stack from sched_switch as start join sched_switch as end on start.prev_pid = end.next_pid
Which will produce the following commands (and -e will also execute them):
echo 's:sched_stack s64 state; char comm[16]; u64 delta; unsigned long stack[];' >> /sys/kernel/tracing/dynamic_events
echo 'hist:keys=prev_pid:__arg_18057_2=prev_state,__arg_18057_4=common_timestamp.usecs,__arg_18057_7=common_stacktrace' >> /sys/kernel/tracing/events/sched/sched_switch/trigger
echo 'hist:keys=next_pid:__state_18057_1=$__arg_18057_2,__comm_18057_3=next_comm,__delta_18057_5=common_timestamp.usecs-$__arg_18057_4,__stack_18057_6=$__arg_18057_7:onmatch(sched.sched_switch).trace(sched_stack,$__state_18057_1,$__comm_18057_3,$__delta_18057_5,$__stack_18057_6)' >> /sys/kernel/tracing/events/sched/sched_switch/trigger
The above creates a synthetic event that creates a stack trace when a task schedules out and records it with the time it scheduled back in. Basically the time a task is off the CPU. It also records the state of the task when it left the CPU (running, blocked, sleeping, etc). It also saves the comm of the task as "comm" (needed for the next command).
~# echo 'hist:keys=state,stack.stacktrace:vals=delta:sort=state,delta if comm == "trace-cmd" && state & 3' > /sys/kernel/tracing/events/synthetic/sched_stack/trigger
The above creates a histogram with buckets per state, per stack, and the value of the total time it was off the CPU for that stack trace. It filters on tasks with "comm == trace-cmd" and only the sleeping and blocked states (1 - sleeping, 2 - blocked).
~# trace-cmd record -p function sleep 1
~# cat /sys/kernel/tracing/events/synthetic/sched_stack/hist | tail -18
{ state: 2, stack.stacktrace __schedule+0x1545/0x3700
schedule+0xe2/0x390
schedule_timeout+0x175/0x200
wait_for_completion_state+0x294/0x440
__wait_rcu_gp+0x247/0x4f0
synchronize_rcu_tasks_generic+0x151/0x230
apply_subsystem_event_filter+0xa2b/0x1300
subsystem_filter_write+0x67/0xc0
vfs_write+0x1e2/0xeb0
ksys_write+0xff/0x1d0
do_syscall_64+0x7b/0x420
entry_SYSCALL_64_after_hwframe+0x76/0x7e} hitcount: 237 delta: 99756288 <<--------------- Delta is 99 seconds!
Totals:
Hits: 525
Entries: 21
Dropped: 0This shows that this particular trace waited for 99 seconds on synchronize_rcu_tasks() in apply_subsystem_event_filter().
In fact, there's a lot of places in the filter code that spends a lot of time waiting for synchronize_rcu_tasks_trace() in order to free the filters.
Add helper functions that will use call_rcu*() variants to asynchronously free the filters. This brings the timings back to normal:
# time trace-cmd record -p function sleep 1 [..] real 0m14.681s user 0m0.335s sys 0m28.616s
And the histogram also shows this:
~# cat /sys/kernel/tracing/events/synthetic/sched_stack/hist | tail -21
{ state: 2, stack.stacktrace __schedule+0x1545/0x3700
schedule+0xe2/0x390
schedule_timeout+0x175/0x200
wait_for_completion_state+0x294/0x440
__wait_rcu_gp+0x247/0x4f0
synchronize_rcu_normal+0x3db/0x5c0
tracing_reset_online_cpus+0x8f/0x1e0
tracing_open+0x335/0x440
do_dentry_open+0x4c6/0x17a0
vfs_open+0x82/0x360
path_openat+0x1a36/0x2990
do_filp_open+0x1c5/0x420
do_sys_openat2+0xed/0x180
__x64_sys_openat+0x108/0x1d0
do_syscall_64+0x7b/0x420} hitcount: 2 delta: 77044
Totals:
Hits: 55
Entries: 28
Dropped: 0Where the total waiting time of synchronize_rcu_tasks_trace() is 77 milliseconds.
--- kernel/trace/trace_events_filter.c | 164 ++++++++++++++++++++++------- 1 file changed, 127 insertions(+), 37 deletions(-)
kernel/trace/trace_events_filter.c +127 -37
@@ -1335,6 +1335,74 @@ static void filter_free_subsystem_preds(struct trace_subsystem_dir *dir, } } +struct filter_list { +struct list_head list; +struct event_filter *filter; +}; + +struct filter_head { +struct list_head list; +struct rcu_head rcu; +}; + + +static void free_filter_list (struct rcu_head *rhp) +{ + 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) { +__free_filter (filter_item->filter); +list_del (&filter_item->list); +kfree (filter_item); + } +kfree (filter_list); +} + +static void free_filter_list_tasks (struct rcu_head *rhp) +{ +call_rcu (rhp, free_filter_list); +} + +/* +* The tracepoint_synchronize_unregister() is a double rcu call. +* It calls synchronize_rcu_tasks_trace() followed by synchronize_rcu(). +* Instead of waiting for it, simply call these via the call_rcu*() +* variants. +*/ +static void delay_free_filter (struct filter_head *head) +{ +call_rcu_tasks_trace (&head->rcu, free_filter_list_tasks); +} + +static void try_delay_free_filter (struct event_filter *filter) +{ +struct filter_head *head; +struct filter_list *item; + + head =kmalloc (sizeof (*head),GFP_KERNEL ); +if (!head) + goto free_now; + +INIT_LIST_HEAD (&head->list); + + item =kmalloc (sizeof (*item),GFP_KERNEL ); +if (!item) { +kfree (head); + goto free_now; + } + + item->filter = filter; +list_add_tail (&item->list, &head->list); +delay_free_filter (head); +return ; + + free_now: +/* Make sure the filter is not being used */ +tracepoint_synchronize_unregister (); +__free_filter (filter); +} +static inline void __free_subsystem_filter (struct trace_event_file *file) {__free_filter (file->filter);
@@ -1342,15 +1410,53 @@ static inline void __free_subsystem_filter(struct trace_event_file *file) }static void filter_free_subsystem_filters (struct trace_subsystem_dir *dir, -struct trace_array *tr) +struct trace_array *tr, +struct event_filter *filter) {struct trace_event_file *file; +struct filter_head *head; +struct filter_list *item; + + head =kmalloc (sizeof (*head),GFP_KERNEL ); +if (!head) + goto free_now; + +INIT_LIST_HEAD (&head->list); + + item =kmalloc (sizeof (*item),GFP_KERNEL ); +if (!item) { +kfree (head); + goto free_now; + } + + item->filter = filter; +list_add_tail (&item->list, &head->list);list_for_each_entry (file, &tr->events, list) {if (file->system != dir)continue ; -__free_subsystem_filter (file); + item =kmalloc (sizeof (*item),GFP_KERNEL ); +if (!item) + goto free_now; + item->filter = file->filter; +list_add_tail (&item->list, &head->list); + file->filter =NULL ; + } + +delay_free_filter (head); +return ; + free_now: +tracepoint_synchronize_unregister (); + +if (head) +free_filter_list (&head->rcu); + +list_for_each_entry (file, &tr->events, list) { +if (file->system != dir || !file->filter) +continue ; +__free_filter (file->filter); } +__free_filter (filter); }int filter_assign_type (const char *type)
@@ -2131,11 +2237,6 @@ static inline void event_clear_filter(struct trace_event_file *file)RCU_INIT_POINTER (file->filter,NULL ); } -struct filter_list { -struct list_head list; -struct event_filter *filter; -}; - static int process_system_preds(struct trace_subsystem_dir *dir, struct trace_array *tr, struct filter_parse_error *pe,
@@ -2144,11 +2245,16 @@ static int process_system_preds(struct trace_subsystem_dir *dir,struct trace_event_file *file;struct filter_list *filter_item;struct event_filter *filter =NULL ; -struct filter_list *tmp; -LIST_HEAD (filter_list); +struct filter_head *filter_list;bool fail = true;int err; + filter_list =kmalloc (sizeof (*filter_list),GFP_KERNEL ); +if (!filter_list) +return -ENOMEM ; + +INIT_LIST_HEAD (&filter_list->list); +list_for_each_entry (file, &tr->events, list) {if (file->system != dir)
@@ -2175,7 +2281,7 @@ static int process_system_preds(struct trace_subsystem_dir *dir,if (!filter_item) goto fail_mem; -list_add_tail (&filter_item->list, &filter_list); +list_add_tail (&filter_item->list, &filter_list->list);/* * Regardless of if this returned an error, we still * replace the filter for the call.
@@ -2195,31 +2301,22 @@ static int process_system_preds(struct trace_subsystem_dir *dir,* Do a synchronize_rcu() and to ensure all calls are * done with them before we free them. */ -tracepoint_synchronize_unregister (); -list_for_each_entry_safe (filter_item, tmp, &filter_list, list) { -__free_filter (filter_item->filter); -list_del (&filter_item->list); -kfree (filter_item); - } +delay_free_filter (filter_list);return 0 ; fail:/* No call succeeded */ -list_for_each_entry_safe (filter_item, tmp, &filter_list, list) { -list_del (&filter_item->list); -kfree (filter_item); - } +free_filter_list (&filter_list->rcu);parse_error (pe,FILT_ERR_BAD_SUBSYS_FILTER ,0 );return -EINVAL ; fail_mem:__free_filter (filter); +/* If any call succeeded, we still need to sync */ if (!fail) -tracepoint_synchronize_unregister (); -list_for_each_entry_safe (filter_item, tmp, &filter_list, list) { -__free_filter (filter_item->filter); -list_del (&filter_item->list); -kfree (filter_item); - } +delay_free_filter (filter_list); +else +free_filter_list (&filter_list->rcu); +return -ENOMEM ; }
@@ -2361,9 +2458,7 @@ int apply_event_filter(struct trace_event_file *file, char *filter_string)event_clear_filter (file); -/* Make sure the filter is not being used */ -tracepoint_synchronize_unregister (); -__free_filter (filter); +try_delay_free_filter (filter);return 0 ; }
@@ -2387,11 +2482,8 @@ int apply_event_filter(struct trace_event_file *file, char *filter_string)event_set_filter (file, filter); -if (tmp) { -/* Make sure the call is done with the filter */ -tracepoint_synchronize_unregister (); -__free_filter (tmp); - } +if (tmp) +try_delay_free_filter (tmp); }return err;
@@ -2417,9 +2509,7 @@ int apply_subsystem_event_filter(struct trace_subsystem_dir *dir, filter = system->filter; system->filter =NULL ;/* Ensure all filters are no longer used */ -tracepoint_synchronize_unregister (); -filter_free_subsystem_filters (dir, tr); -__free_filter (filter); +filter_free_subsystem_filters (dir, tr, filter);return 0 ; }
Signature · 1 line
2.47.2
Steven Rostedt
maintainerPATCH 2/3 ring-buffer: Fix buffer locking in ring_buffer_subbuf_order_set()
In reply to Steven RostedtFrom: Dmitry Antipov <[email protected]>
Enlarge the critical section in ring_buffer_subbuf_order_set() to ensure that error handling takes place with per-buffer mutex held, thus preventing list corruption and other concurrency-related issues.
--- kernel/trace/ring_buffer.c | 4 +--- 1 file changed, 1 insertion(+), 3 deletions(-)
kernel/trace/ring_buffer.c +1 -3
@@ -6795,7 +6795,7 @@ int ring_buffer_subbuf_order_set(struct trace_buffer *buffer, int order) old_size = buffer->subbuf_size;/* prevent another thread from changing buffer sizes */ -mutex_lock (&buffer->mutex); +guard (mutex)(&buffer->mutex);atomic_inc (&buffer->record_disabled);/* Make sure all commits have finished */
@@ -6900,7 +6900,6 @@ int ring_buffer_subbuf_order_set(struct trace_buffer *buffer, int order) }atomic_dec (&buffer->record_disabled); -mutex_unlock (&buffer->mutex);return 0 ;
@@ -6909,7 +6908,6 @@ int ring_buffer_subbuf_order_set(struct trace_buffer *buffer, int order) buffer->subbuf_size = old_size;atomic_dec (&buffer->record_disabled); -mutex_unlock (&buffer->mutex);for_each_buffer_cpu (buffer, cpu) { cpu_buffer = buffer->buffers[cpu];
Signature · 1 line
2.47.2
Steven Rostedt
maintainerPATCH 3/3 tracing: PM: Remove unused clock events
In reply to Steven RostedtFrom: Steven Rostedt <[email protected]>
The events clock_enable, clock_disable, and clock_set_rate were added back in 2010. In 2011 they were used by the arm architecture but removed in 2013. These events add around 7K of memory which was wasted for the last 12 years.
Remove them.
--- include/trace/events/power.h | 47 ------------------------------------ 1 file changed, 47 deletions(-)
include/trace/events/power.h +0 -47
@@ -337,53 +337,6 @@ DEFINE_EVENT(wakeup_source, wakeup_source_deactivate,TP_ARGS (name, state) ); -/* -* The clock events are used for clock enable/disable and for -* clock rate change -*/ -DECLARE_EVENT_CLASS (clock, - - TP_PROTO(const char *name, unsigned int state, unsigned int cpu_id), - -TP_ARGS (name, state, cpu_id), - -TP_STRUCT__entry ( - __string( name, name ) - __field( u64, state ) -__field ( u64, cpu_id ) - ), - -TP_fast_assign ( - __assign_str(name); - __entry->state = state; - __entry->cpu_id = cpu_id; - ), - -TP_printk ("%s state=%lu cpu_id=%lu" ,__get_str (name), - (unsigned long )__entry->state, (unsigned long )__entry->cpu_id) -); - -DEFINE_EVENT (clock, clock_enable, - - TP_PROTO(const char *name, unsigned int state, unsigned int cpu_id), - -TP_ARGS (name, state, cpu_id) -); - -DEFINE_EVENT (clock, clock_disable, - - TP_PROTO(const char *name, unsigned int state, unsigned int cpu_id), - -TP_ARGS (name, state, cpu_id) -); - -DEFINE_EVENT (clock, clock_set_rate, - - TP_PROTO(const char *name, unsigned int state, unsigned int cpu_id), - -TP_ARGS (name, state, cpu_id) -); -/* * The power domain events are used for power domains transitions */
Signature · 1 line
2.47.2