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SubjectRe: [PATCH] uprobes: Use synchronize_rcu() not synchronize_sched()
On 08/09, Steven Rostedt wrote:
>
> --- a/kernel/trace/trace_uprobe.c
> +++ b/kernel/trace/trace_uprobe.c
> @@ -952,7 +952,7 @@ probe_event_disable(struct trace_uprobe *tu, struct trace_event_file *file)
>
> list_del_rcu(&link->list);
> /* synchronize with u{,ret}probe_trace_func */
> - synchronize_sched();
> + synchronize_rcu();

Can't we change uprobe_trace_func() and uretprobe_trace_func() to use
rcu_read_lock_sched() instead? It is more cheap.


Hmm. probe_event_enable() does list_del + kfree on failure, this doesn't
look right... Not only because kfree() can race with list_for_each_entry_rcu(),
we should not put the 1st link on list until uprobe_buffer_enable().

Does the patch below make sense or I am confused?

Oleg.


--- x/kernel/trace/trace_uprobe.c
+++ x/kernel/trace/trace_uprobe.c
@@ -896,8 +896,6 @@ probe_event_enable(struct trace_uprobe *
return -ENOMEM;

link->file = file;
- list_add_tail_rcu(&link->list, &tu->tp.files);
-
tu->tp.flags |= TP_FLAG_TRACE;
} else {
if (tu->tp.flags & TP_FLAG_TRACE)
@@ -909,7 +907,7 @@ probe_event_enable(struct trace_uprobe *
WARN_ON(!uprobe_filter_is_empty(&tu->filter));

if (enabled)
- return 0;
+ goto add;

ret = uprobe_buffer_enable();
if (ret)
@@ -920,7 +918,8 @@ probe_event_enable(struct trace_uprobe *
ret = uprobe_register(tu->inode, tu->offset, &tu->consumer);
if (ret)
goto err_buffer;
-
+ add:
+ list_add_tail_rcu(&link->list, &tu->tp.files);
return 0;

err_buffer:
@@ -928,7 +927,6 @@ probe_event_enable(struct trace_uprobe *

err_flags:
if (file) {
- list_del(&link->list);
kfree(link);
tu->tp.flags &= ~TP_FLAG_TRACE;
} else {
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