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Unknown reader errors should close reader/tailer to avoid mtail looping on broken fds. #993

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Unknown reader errors should close reader/tailer to avoid mtail looping on broken fds. #993

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14 changes: 13 additions & 1 deletion internal/tailer/logstream/filestream.go
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Original file line number Diff line number Diff line change
Expand Up @@ -124,8 +124,20 @@ func (fs *fileStream) stream(ctx context.Context, wg *sync.WaitGroup, waker wake
}
// Close this stream.
return
} else {
glog.Infof("stream(%s): read error: %v", fs.sourcename, err)
// We got unknown stream read error != syscall.ESTALE which currently we don't know how to handle.
// Those might be read error: (is a directory|bad file descriptor|...) etc.
// Without this patch mtail istarting to loop on broken fds that are gone/incorrect,
// start consuming a lot of CPU cycles, and can't handle signals besides SIGKILL.
// If we end up in such unrecovarable/unhandled (for now) situation, it is better to use fail fast approach.
// We close the reader and the tailer for this source and let the tailer pick-up the new file(s) if any on its own later.
// Those read error: (is directory|bad file descriptor) can happen if we mtail files under mounts, and mounts are gone.
// Those might be docker/container/etc. setups where mtail is running on host.
lr.Finish(ctx)
close(fs.lines)
return
}
glog.Infof("stream(%s): read error: %v", fs.sourcename, err)
}

// If we have read no bytes and are at EOF, check for truncation and rotation.
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