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McKenney" , "Joel Fernandes (Google)" , "Steven Rostedt (VMware)" , Sasha Levin Subject: [PATCH 5.4 140/309] ftrace: Protect ftrace_graph_hash with ftrace_sync Date: Mon, 10 Feb 2020 04:31:36 -0800 Message-Id: <20200210122419.796009961@linuxfoundation.org> X-Mailer: git-send-email 2.25.0 In-Reply-To: <20200210122406.106356946@linuxfoundation.org> References: <20200210122406.106356946@linuxfoundation.org> User-Agent: quilt/0.66 MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Sender: stable-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: stable@vger.kernel.org From: Steven Rostedt (VMware) [ Upstream commit 54a16ff6f2e50775145b210bcd94d62c3c2af117 ] 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: b9b0c831bed26 ("ftrace: Convert graph filter to use hash tables") Reported-by: "Paul E. McKenney" Reviewed-by: Joel Fernandes (Google) Signed-off-by: Steven Rostedt (VMware) Signed-off-by: Sasha Levin --- kernel/trace/ftrace.c | 11 +++++++++-- kernel/trace/trace.h | 2 ++ 2 files changed, 11 insertions(+), 2 deletions(-) diff --git a/kernel/trace/ftrace.c b/kernel/trace/ftrace.c index d297a8bdc681a..407d8bf4ed93e 100644 --- a/kernel/trace/ftrace.c +++ b/kernel/trace/ftrace.c @@ -5378,8 +5378,15 @@ 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); } diff --git a/kernel/trace/trace.h b/kernel/trace/trace.h index 08647723cfab9..a3c29d5fcc616 100644 --- a/kernel/trace/trace.h +++ b/kernel/trace/trace.h @@ -947,6 +947,7 @@ 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()); @@ -999,6 +1000,7 @@ 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()); -- 2.20.1