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ftrace: Protect ftrace_graph_hash with ftrace_sync

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As function_graph tracer can run when RCU is not "watching", it can not be
protected by synchronize_rcu() it requires running a task on each CPU before
it can be freed. Calling schedule_on_each_cpu(ftrace_sync) needs to be used.

Link: https://lore.kernel.org/r/20200205131110.GT2935@paulmck-ThinkPad-P72

Cc: stable@vger.kernel.org
Fixes: b9b0c831be ("ftrace: Convert graph filter to use hash tables")
Reported-by: "Paul E. McKenney" <paulmck@kernel.org>
Reviewed-by: Joel Fernandes (Google) <joel@joelfernandes.org>
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
This commit is contained in:
Steven Rostedt (VMware) 2020-02-05 09:20:32 -05:00
parent 16052dd5bd
commit 54a16ff6f2
2 changed files with 11 additions and 2 deletions
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11
kernel/trace/ftrace.c
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@ -5867,8 +5867,15 @@ ftrace_graph_release(struct inode *inode, struct file *file)
mutex_unlock(&graph_lock);
/* Wait till all users are no longer using the old hash */
synchronize_rcu();
/*
* We need to do a hard force of sched synchronization.
* This is because we use preempt_disable() to do RCU, but
* the function tracers can be called where RCU is not watching
* (like before user_exit()). We can not rely on the RCU
* infrastructure to do the synchronization, thus we must do it
* ourselves.
*/
schedule_on_each_cpu(ftrace_sync);
free_ftrace_hash(old_hash);
}

2
kernel/trace/trace.h
View File

@ -979,6 +979,7 @@ static inline int ftrace_graph_addr(struct ftrace_graph_ent *trace)
* Have to open code "rcu_dereference_sched()" because the
* function graph tracer can be called when RCU is not
* "watching".
* Protected with schedule_on_each_cpu(ftrace_sync)
*/
hash = rcu_dereference_protected(ftrace_graph_hash, !preemptible());
@ -1031,6 +1032,7 @@ static inline int ftrace_graph_notrace_addr(unsigned long addr)
* Have to open code "rcu_dereference_sched()" because the
* function graph tracer can be called when RCU is not
* "watching".
* Protected with schedule_on_each_cpu(ftrace_sync)
*/
notrace_hash = rcu_dereference_protected(ftrace_graph_notrace_hash,
!preemptible());