* [for-next][PATCH 1/5] ftrace: Protect ftrace_graph_hash with ftrace_sync [not found] <20200205222110.912457436@goodmis.org> @ 2020-02-05 22:21 ` Steven Rostedt 2020-02-05 22:28 ` Paul E. McKenney 0 siblings, 1 reply; 2+ messages in thread From: Steven Rostedt @ 2020-02-05 22:21 UTC (permalink / raw) To: linux-kernel Cc: Ingo Molnar, Andrew Morton, stable, Paul E. McKenney, Joel Fernandes (Google) From: "Steven Rostedt (VMware)" <rostedt@goodmis.org> 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" <paulmck@kernel.org> Reviewed-by: Joel Fernandes (Google) <joel@joelfernandes.org> Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org> --- 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 481ede3eac13..3f7ee102868a 100644 --- a/kernel/trace/ftrace.c +++ b/kernel/trace/ftrace.c @@ -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); } diff --git a/kernel/trace/trace.h b/kernel/trace/trace.h index 8c52f5de9384..3c75d29bd861 100644 --- a/kernel/trace/trace.h +++ b/kernel/trace/trace.h @@ -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()); -- 2.24.1 ^ permalink raw reply related [flat|nested] 2+ messages in thread
* Re: [for-next][PATCH 1/5] ftrace: Protect ftrace_graph_hash with ftrace_sync 2020-02-05 22:21 ` [for-next][PATCH 1/5] ftrace: Protect ftrace_graph_hash with ftrace_sync Steven Rostedt @ 2020-02-05 22:28 ` Paul E. McKenney 0 siblings, 0 replies; 2+ messages in thread From: Paul E. McKenney @ 2020-02-05 22:28 UTC (permalink / raw) To: Steven Rostedt Cc: linux-kernel, Ingo Molnar, Andrew Morton, stable, Joel Fernandes (Google) On Wed, Feb 05, 2020 at 05:21:11PM -0500, Steven Rostedt wrote: > From: "Steven Rostedt (VMware)" <rostedt@goodmis.org> > > 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" <paulmck@kernel.org> > Reviewed-by: Joel Fernandes (Google) <joel@joelfernandes.org> > Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org> Nice! If there is much more call for this, perhaps I should take a hint from the ftrace_sync() comment and add synchronize_rcu_rude(). ;-) Reviewed-by: "Paul E. McKenney" <paulmck@kernel.org> > --- > 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 481ede3eac13..3f7ee102868a 100644 > --- a/kernel/trace/ftrace.c > +++ b/kernel/trace/ftrace.c > @@ -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); > } > diff --git a/kernel/trace/trace.h b/kernel/trace/trace.h > index 8c52f5de9384..3c75d29bd861 100644 > --- a/kernel/trace/trace.h > +++ b/kernel/trace/trace.h > @@ -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()); > -- > 2.24.1 > > ^ permalink raw reply [flat|nested] 2+ messages in thread
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2020-02-05 22:21 ` [for-next][PATCH 1/5] ftrace: Protect ftrace_graph_hash with ftrace_sync Steven Rostedt
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