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author | Lai Jiangshan <laijs@cn.fujitsu.com> | 2009-05-18 19:35:34 +0800 |
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committer | Frederic Weisbecker <fweisbec@gmail.com> | 2009-05-25 23:53:41 +0200 |
commit | 4f5359685af6de7dca101393dc606620adbe963f (patch) | |
tree | 1f9dc3fb9299008daa6a5fb6f03945008ea4a4f9 /kernel/trace/trace_output.h | |
parent | 5537937696c55530447c20aa27daccb8d0d29b33 (diff) | |
download | kernel_samsung_tuna-4f5359685af6de7dca101393dc606620adbe963f.zip kernel_samsung_tuna-4f5359685af6de7dca101393dc606620adbe963f.tar.gz kernel_samsung_tuna-4f5359685af6de7dca101393dc606620adbe963f.tar.bz2 |
tracing: add trace_event_read_lock()
I found that there is nothing to protect event_hash in
ftrace_find_event(). Rcu protects the event hashlist
but not the event itself while we use it after its extraction
through ftrace_find_event().
This lack of a proper locking in this spot opens a race
window between any event dereferencing and module removal.
Eg:
--Task A--
print_trace_line(trace) {
event = find_ftrace_event(trace)
--Task B--
trace_module_remove_events(mod) {
list_trace_events_module(ev, mod) {
unregister_ftrace_event(ev->event) {
hlist_del(ev->event->node)
list_del(....)
}
}
}
|--> module removed, the event has been dropped
--Task A--
event->print(trace); // Dereferencing freed memory
If the event retrieved belongs to a module and this module
is concurrently removed, we may end up dereferencing a data
from a freed module.
RCU could solve this, but it would add latency to the kernel and
forbid tracers output callbacks to call any sleepable code.
So this fix converts 'trace_event_mutex' to a read/write semaphore,
and adds trace_event_read_lock() to protect ftrace_find_event().
[ Impact: fix possible freed memory dereference in ftrace ]
Signed-off-by: Lai Jiangshan <laijs@cn.fujitsu.com>
Acked-by: Steven Rostedt <rostedt@goodmis.org>
LKML-Reference: <4A114806.7090302@cn.fujitsu.com>
Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com>
Diffstat (limited to 'kernel/trace/trace_output.h')
-rw-r--r-- | kernel/trace/trace_output.h | 2 |
1 files changed, 2 insertions, 0 deletions
diff --git a/kernel/trace/trace_output.h b/kernel/trace/trace_output.h index 6e220a8..ac240e7 100644 --- a/kernel/trace/trace_output.h +++ b/kernel/trace/trace_output.h @@ -20,6 +20,8 @@ extern int seq_print_user_ip(struct trace_seq *s, struct mm_struct *mm, extern int trace_print_context(struct trace_iterator *iter); extern int trace_print_lat_context(struct trace_iterator *iter); +extern void trace_event_read_lock(void); +extern void trace_event_read_unlock(void); extern struct trace_event *ftrace_find_event(int type); extern enum print_line_t trace_nop_print(struct trace_iterator *iter, |