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authorFrederic Weisbecker <fweisbec@gmail.com>2010-02-02 23:34:40 +0100
committerFrederic Weisbecker <fweisbec@gmail.com>2010-03-10 14:26:07 +0100
commitdb2c4c7791cd04512093d05afc693c3511a65fd7 (patch)
tree11ad51f5ec2010e32edde2dea5696f90822435f4
parent65f2ed2b2fa6034ef9890b60c8fd39fbe76b9d37 (diff)
lockdep: Move lock events under lockdep recursion protection
There are rcu locked read side areas in the path where we submit a trace event. And these rcu_read_(un)lock() trigger lock events, which create recursive events. One pair in do_perf_sw_event: __lock_acquire | |--96.11%-- lock_acquire | | | |--27.21%-- do_perf_sw_event | | perf_tp_event | | | | | |--49.62%-- ftrace_profile_lock_release | | | lock_release | | | | | | | |--33.85%-- _raw_spin_unlock Another pair in perf_output_begin/end: __lock_acquire |--23.40%-- perf_output_begin | | __perf_event_overflow | | perf_swevent_overflow | | perf_swevent_add | | perf_swevent_ctx_event | | do_perf_sw_event | | perf_tp_event | | | | | |--55.37%-- ftrace_profile_lock_acquire | | | lock_acquire | | | | | | | |--37.31%-- _raw_spin_lock The problem is not that much the trace recursion itself, as we have a recursion protection already (though it's always wasteful to recurse). But the trace events are outside the lockdep recursion protection, then each lockdep event triggers a lock trace, which will trigger two other lockdep events. Here the recursive lock trace event won't be taken because of the trace recursion, so the recursion stops there but lockdep will still analyse these new events: To sum up, for each lockdep events we have: lock_*() | trace lock_acquire | ----- rcu_read_lock() | | | lock_acquire() | | | trace_lock_acquire() (stopped) | | | lockdep analyze | ----- rcu_read_unlock() | lock_release | trace_lock_release() (stopped) | lockdep analyze And you can repeat the above two times as we have two rcu read side sections when we submit an event. This is fixed in this patch by moving the lock trace event under the lockdep recursion protection. Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Arnaldo Carvalho de Melo <acme@redhat.com> Cc: Steven Rostedt <rostedt@goodmis.org> Cc: Paul Mackerras <paulus@samba.org> Cc: Hitoshi Mitake <mitake@dcl.info.waseda.ac.jp> Cc: Li Zefan <lizf@cn.fujitsu.com> Cc: Lai Jiangshan <laijs@cn.fujitsu.com> Cc: Masami Hiramatsu <mhiramat@redhat.com> Cc: Jens Axboe <jens.axboe@oracle.com>
-rw-r--r--kernel/lockdep.c9
1 files changed, 3 insertions, 6 deletions
diff --git a/kernel/lockdep.c b/kernel/lockdep.c
index 0c30d0455de..65b5f5b7c29 100644
--- a/kernel/lockdep.c
+++ b/kernel/lockdep.c
@@ -3211,8 +3211,6 @@ void lock_acquire(struct lockdep_map *lock, unsigned int subclass,
{
unsigned long flags;
- trace_lock_acquire(lock, subclass, trylock, read, check, nest_lock, ip);
-
if (unlikely(current->lockdep_recursion))
return;
@@ -3220,6 +3218,7 @@ void lock_acquire(struct lockdep_map *lock, unsigned int subclass,
check_flags(flags);
current->lockdep_recursion = 1;
+ trace_lock_acquire(lock, subclass, trylock, read, check, nest_lock, ip);
__lock_acquire(lock, subclass, trylock, read, check,
irqs_disabled_flags(flags), nest_lock, ip, 0);
current->lockdep_recursion = 0;
@@ -3232,14 +3231,13 @@ void lock_release(struct lockdep_map *lock, int nested,
{
unsigned long flags;
- trace_lock_release(lock, nested, ip);
-
if (unlikely(current->lockdep_recursion))
return;
raw_local_irq_save(flags);
check_flags(flags);
current->lockdep_recursion = 1;
+ trace_lock_release(lock, nested, ip);
__lock_release(lock, nested, ip);
current->lockdep_recursion = 0;
raw_local_irq_restore(flags);
@@ -3413,8 +3411,6 @@ void lock_contended(struct lockdep_map *lock, unsigned long ip)
{
unsigned long flags;
- trace_lock_contended(lock, ip);
-
if (unlikely(!lock_stat))
return;
@@ -3424,6 +3420,7 @@ void lock_contended(struct lockdep_map *lock, unsigned long ip)
raw_local_irq_save(flags);
check_flags(flags);
current->lockdep_recursion = 1;
+ trace_lock_contended(lock, ip);
__lock_contended(lock, ip);
current->lockdep_recursion = 0;
raw_local_irq_restore(flags);