d58f4e9b7b
Since Go1.8, different types of GC mark workers were annotated and the annotation strings were recorded during StartTrace. This change fixes two issues around the use of traceString from StartTrace here. 1) "failed to parse trace: no consistent ordering of events possible" This issue is a result of a missing 'batch' event entry. For efficient tracing, tracer maintains system allocated buffers and once a buffer is full, it is Flushed out for writing. Moreover, tracing assumes all the records in the same buffer (batch) are already ordered and implements more optimization in encoding and defers the completing order reconstruction till the trace parsing time. Thus, when a Flush happens and a new buffer is used, the new buffer should contain an event to indicate the start of a new batch. Before this CL, the batch entry was written only by traceEvent only when the buffer position is 0 and wasn't written when flush occurs during traceString. This CL fixes it by moving the batch entry write to the traceFlush. 2) crash during tracing due to invalid memory access, or during parsing due to duplicate string entries This issue is a result of memory allocation during traceString calls. Execution tracer traces some memory allocation activities. Before this CL, traceString took the buffer address (*traceBuf) and mutated the buffer. If memory tracing occurs in the meantime from the same P, the allocation tracing (traceEvent) will take the same buffer address through the pointer to the buffer address (**traceBuf), and mutate the buffer. As a result, one of the followings can happen: - the allocation record is overwritten by the following trace string record (data loss) - if buffer flush occurs during the allocation tracing, traceString will attempt to write the string record to the old buffer and eventually causes invalid memory access crash. - or flush on the same buffer can occur twice (once from the memory allocation, and once from the string record write), and in this case the trace can contain the same data twice and the parse will complain about duplicate string record entries. This CL fixes the second issue by making the traceString take **traceBuf (*traceBufPtr). Change-Id: I24f629758625b38e1916fbfc7d7be6ea210586af Reviewed-on: https://go-review.googlesource.com/50873 Run-TryBot: Austin Clements <austin@google.com> Run-TryBot: Hyang-Ah Hana Kim <hyangah@gmail.com> TryBot-Result: Gobot Gobot <gobot@golang.org> Reviewed-by: Austin Clements <austin@google.com> |
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