path: root/init
diff options
authorSteven Rostedt (VMware) <rostedt@goodmis.org>2021-01-29 10:13:53 -0500
committerSteven Rostedt (VMware) <rostedt@goodmis.org>2021-01-29 15:07:32 -0500
commit7e0a9220467dbcfdc5bc62825724f3e52e50ab31 (patch)
treeff6cfcbcbbad6709d663355fbed19ab4a2269d02 /init
parent6ee1d745b7c9fd573fba142a2efdad76a9f1cb04 (diff)
fgraph: Initialize tracing_graph_pause at task creation
On some archs, the idle task can call into cpu_suspend(). The cpu_suspend() will disable or pause function graph tracing, as there's some paths in bringing down the CPU that can have issues with its return address being modified. The task_struct structure has a "tracing_graph_pause" atomic counter, that when set to something other than zero, the function graph tracer will not modify the return address. The problem is that the tracing_graph_pause counter is initialized when the function graph tracer is enabled. This can corrupt the counter for the idle task if it is suspended in these architectures. CPU 1 CPU 2 ----- ----- do_idle() cpu_suspend() pause_graph_tracing() task_struct->tracing_graph_pause++ (0 -> 1) start_graph_tracing() for_each_online_cpu(cpu) { ftrace_graph_init_idle_task(cpu) task-struct->tracing_graph_pause = 0 (1 -> 0) unpause_graph_tracing() task_struct->tracing_graph_pause-- (0 -> -1) The above should have gone from 1 to zero, and enabled function graph tracing again. But instead, it is set to -1, which keeps it disabled. There's no reason that the field tracing_graph_pause on the task_struct can not be initialized at boot up. Cc: stable@vger.kernel.org Fixes: 380c4b1411ccd ("tracing/function-graph-tracer: append the tracing_graph_flag") Bugzilla: https://bugzilla.kernel.org/show_bug.cgi?id=211339 Reported-by: pierre.gondois@arm.com Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
Diffstat (limited to 'init')
1 files changed, 2 insertions, 1 deletions
diff --git a/init/init_task.c b/init/init_task.c
index 8a992d73e6fb..3711cdaafed2 100644
--- a/init/init_task.c
+++ b/init/init_task.c
@@ -198,7 +198,8 @@ struct task_struct init_task
.lockdep_recursion = 0,
- .ret_stack = NULL,
+ .ret_stack = NULL,
+ .tracing_graph_pause = ATOMIC_INIT(0),
.trace_recursion = 0,

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