path: root/include/linux
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authorSteven Rostedt (VMware) <rostedt@goodmis.org>2018-07-09 17:48:54 -0400
committerTejun Heo <tj@kernel.org>2018-07-11 10:48:47 -0700
commite4f8d81c738db6d3ffdabfb8329aa2feaa310699 (patch)
tree97153959e7c625bc49850709149a1faa5146a70e /include/linux
parentMerge tag 'mips_fixes_4.18_3' of git://git.kernel.org/pub/scm/linux/kernel/git/mips/linux (diff)
cgroup/tracing: Move taking of spin lock out of trace event handlers
It is unwise to take spin locks from the handlers of trace events. Mainly, because they can introduce lockups, because it introduces locks in places that are normally not tested. Worse yet, because trace events are tucked away in the include/trace/events/ directory, locks that are taken there are forgotten about. As a general rule, I tell people never to take any locks in a trace event handler. Several cgroup trace event handlers call cgroup_path() which eventually takes the kernfs_rename_lock spinlock. This injects the spinlock in the code without people realizing it. It also can cause issues for the PREEMPT_RT patch, as the spinlock becomes a mutex, and the trace event handlers are called with preemption disabled. By moving the calculation of the cgroup_path() out of the trace event handlers and into a macro (surrounded by a trace_cgroup_##type##_enabled()), then we could place the cgroup_path into a string, and pass that to the trace event. Not only does this remove the taking of the spinlock out of the trace event handler, but it also means that the cgroup_path() only needs to be called once (it is currently called twice, once to get the length to reserver the buffer for, and once again to get the path itself. Now it only needs to be done once. Reported-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de> Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org> Signed-off-by: Tejun Heo <tj@kernel.org>
Diffstat (limited to 'include/linux')
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