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https://issues.apache.org/jira/browse/HDFS-10182?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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zhouyingchao updated HDFS-10182:
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Description:
In DFSInputStream::hedgedFetchBlockByteRange, during the first attempt, the
passed-in buf from the caller is passed to another thread to fill. If the
first attempt is timed out, the second attempt would be issued with another
ByteBuffer. Now suppose the second attempt wins and the first attempt is
blocked somewhere in the IO path. The second attempt's result would be copied
to the buf provided by the caller and then caller would think the pread is all
set. Later the caller might use the buf to do something else (for e.g. read
another chunk of data), however, the first attempt in earlier
hedgedFetchBlockByteRange might get some data and fill into the buf ...
If this happens, the caller's buf would then be corrupted.
To fix the issue, we should allocate a temp buf for the first attempt too.
was:
In DFSInputStream::hedgedFetchBlockByteRange, the passed-in buf from the caller
is passed to another thread to fill in the first attempt. If the first attempt
is timed out, the second attempt would be issued with another ByteBuffer. Now
suppose the second attempt wins and the first attempt is blocked somewhere in
the IO path. The second attempt's result would be copied to the buf provided by
the caller and then caller would think the pread is all set. Later the caller
might use the buf to do something else (for e.g. read another chunk of data),
however, the first attempt in earlier hedgedFetchBlockByteRange might get some
data and fill into the buf ...
If this happens, the caller's buf would then be corrupted.
To fix the issue, we should allocate a temp buf for the first attempt too.
> Hedged read might overwrite user's buf
> --------------------------------------
>
> Key: HDFS-10182
> URL: https://issues.apache.org/jira/browse/HDFS-10182
> Project: Hadoop HDFS
> Issue Type: Bug
> Reporter: zhouyingchao
> Assignee: zhouyingchao
> Attachments: HDFS-10182-001.patch
>
>
> In DFSInputStream::hedgedFetchBlockByteRange, during the first attempt, the
> passed-in buf from the caller is passed to another thread to fill. If the
> first attempt is timed out, the second attempt would be issued with another
> ByteBuffer. Now suppose the second attempt wins and the first attempt is
> blocked somewhere in the IO path. The second attempt's result would be copied
> to the buf provided by the caller and then caller would think the pread is
> all set. Later the caller might use the buf to do something else (for e.g.
> read another chunk of data), however, the first attempt in earlier
> hedgedFetchBlockByteRange might get some data and fill into the buf ...
> If this happens, the caller's buf would then be corrupted.
> To fix the issue, we should allocate a temp buf for the first attempt too.
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