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Bug #861

UST subbuffers silently dropped on moderate trace traffic

Added by Mathieu Desnoyers almost 6 years ago. Updated almost 6 years ago.

Status:
Resolved
Priority:
Critical
Target version:
Start date:
11/18/2014
Due date:
% Done:

100%

Estimated time:

Description

lttng-tools commit 02b3d1769d5f8a33e4109b1e681141c9295dfda6 introduced an important regression for lttng-ust tracing in the consumer daemon: after reading a sub-buffer, a check has been added to see whether there are more sub-buffers available to read, and if it is the case, it ensures the wakeup pipe will be awakened again.

The issue lies in the use of ustctl_put_next_subbuf() in this check. This acts as if the sub-buffer has been read, when in reality it has not been read. It therefore trashes the data contained by this sub-buffer.

This check should use ustctl_put_subbuf(), which does not move the consumer position.

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