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由 Steven Rostedt 提交于
There's a race condition between the setting of a new tracer and the update of the max trace buffers (the swap). When a new tracer is added, it sets current_trace to nop_trace before disabling the old tracer. At this moment, if the old tracer uses update_max_tr(), the update may trigger the warning against !current_trace->use_max-tr, as nop_trace doesn't have that set. As update_max_tr() requires that interrupts be disabled, we can add a check to see if current_trace == nop_trace and bail if it does. Then when disabling the current_trace, set it to nop_trace and run synchronize_sched(). This will make sure all calls to update_max_tr() have completed (it was called with interrupts disabled). As a clean up, this commit also removes shrinking and recreating the max_tr buffer if the old and new tracers both have use_max_tr set. The old way use to always shrink the buffer, and then expand it for the next tracer. This is a waste of time. Signed-off-by: NSteven Rostedt <rostedt@goodmis.org>
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