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From "zhouyingchao (JIRA)" <j...@apache.org>
Subject [jira] [Updated] (HDFS-10182) Hedged read might overwrite user's buf
Date Fri, 18 Mar 2016 09:17:33 GMT

     [ https://issues.apache.org/jira/browse/HDFS-10182?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
]

zhouyingchao updated HDFS-10182:
--------------------------------
    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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