diff options
| author | Davidlohr Bueso <dave@stgolabs.net> | 2020-09-06 18:33:26 -0700 |
|---|---|---|
| committer | Steven Rostedt (VMware) <rostedt@goodmis.org> | 2020-09-21 21:06:02 -0400 |
| commit | 40d14da383670db21a09e63d52db8dee9b77741e (patch) | |
| tree | 4913385409f94966a7932c13a3c09f21c0109f2d /kernel/trace/fgraph.c | |
| parent | eb8d8b4c9848b200586aa98e105b39f159656ba6 (diff) | |
fgraph: Convert ret_stack tasklist scanning to rcu
It seems that alloc_retstack_tasklist() can also take a lockless
approach for scanning the tasklist, instead of using the big global
tasklist_lock. For this we also kill another deprecated and rcu-unsafe
tsk->thread_group user replacing it with for_each_process_thread(),
maintaining semantics.
Here tasklist_lock does not protect anything other than the list
against concurrent fork/exit. And considering that the whole thing
is capped by FTRACE_RETSTACK_ALLOC_SIZE (32), it should not be a
problem to have a pontentially stale, yet stable, list. The task cannot
go away either, so we don't risk racing with ftrace_graph_exit_task()
which clears the retstack.
The tsk->ret_stack management is not protected by tasklist_lock, being
serialized with the corresponding publish/subscribe barriers against
concurrent ftrace_push_return_trace(). In addition this plays nicer
with cachelines by avoiding two atomic ops in the uncontended case.
Link: https://lkml.kernel.org/r/20200907013326.9870-1-dave@stgolabs.net
Acked-by: Oleg Nesterov <oleg@redhat.com>
Signed-off-by: Davidlohr Bueso <dbueso@suse.de>
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
Diffstat (limited to 'kernel/trace/fgraph.c')
| -rw-r--r-- | kernel/trace/fgraph.c | 8 |
1 files changed, 4 insertions, 4 deletions
diff --git a/kernel/trace/fgraph.c b/kernel/trace/fgraph.c index 1af321dec0f1..5658f13037b3 100644 --- a/kernel/trace/fgraph.c +++ b/kernel/trace/fgraph.c @@ -387,8 +387,8 @@ static int alloc_retstack_tasklist(struct ftrace_ret_stack **ret_stack_list) } } - read_lock(&tasklist_lock); - do_each_thread(g, t) { + rcu_read_lock(); + for_each_process_thread(g, t) { if (start == end) { ret = -EAGAIN; goto unlock; @@ -403,10 +403,10 @@ static int alloc_retstack_tasklist(struct ftrace_ret_stack **ret_stack_list) smp_wmb(); t->ret_stack = ret_stack_list[start++]; } - } while_each_thread(g, t); + } unlock: - read_unlock(&tasklist_lock); + rcu_read_unlock(); free: for (i = start; i < end; i++) kfree(ret_stack_list[i]); |