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List: linux-aio
Subject: BUG REPORT: aio occasionally returns duplicate completion events in 4.4.0 kernel
From: Geoffrey Blake <Geoffrey.Blake () arm ! com>
Date: 2016-09-08 20:05:41
Message-ID: CBAD7263-5851-4ECB-9EAD-077C76E01300 () arm ! com
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Hi,
I am working on an application that leverages the Linux aio facility and I am \
occasionally seeing duplicate completion events being returned from io_getevents(). \
My application uses the iocb.data field to store a pointer to an object that \
maintains state for a single IO operation, upon the first completion this object is \
valid and is subsequently freed. My application crashes when a duplicate completion \
appears and tries to access the already freed object pointed to by the duplicate \
event.
To help with trying to catch when duplicates appear and work-around the issues I see, \
I have been running a patched kernel that adds an extra user_data field to aio_kiocb, \
and leverages reserved2 in iocb and res2 in io_event to track a sequence number for \
the object I store in iocb to detect a duplicate when the sequence numbers in the \
object do not match the one stored in the iocb. So far this seems to be working, but \
the bug appears sporadically and is hard to reproduce.
Please let me know if there is anything I can do to help track down this bug (debug \
settings to activate), or if you want more information.
Thanks,
Geoffrey Blake
Staff Research Engineer
5707 Southwest Pkwy
Encino Trace
Bld 1 Suite 100, Austin TX 78735
T +(1) 512-329-7263
IMPORTANT NOTICE: The contents of this email and any attachments are confidential and \
may also be privileged. If you are not the intended recipient, please notify the \
sender immediately and do not disclose the contents to any other person, use it for \
any purpose, or store or copy the information in any medium. Thank you.
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<p class="MsoNormal"><span style="font-size:11.0pt">Hi, <o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt">I am working on an application \
that leverages the Linux aio facility and I am occasionally seeing duplicate \
completion events being returned from io_getevents(). My application uses the \
iocb.data field to store a pointer to an object that maintains state for a single IO \
operation, upon the first completion this object is valid and is subsequently \
freed. My application crashes when a duplicate completion appears and tries to \
access the already freed object pointed to by the duplicate event. \
<o:p></o:p></span></p> <p class="MsoNormal"><span \
style="font-size:11.0pt"><o:p> </o:p></span></p> <p class="MsoNormal"><span \
style="font-size:11.0pt">To help with trying to catch when duplicates appear and \
work-around the issues I see, I have been running a patched kernel that adds an extra \
user_data field to aio_kiocb, and leverages reserved2 in iocb and res2 in io_event \
to track a sequence number for the object I store in iocb to detect a duplicate when \
the sequence numbers in the object do not match the one stored in the iocb. So \
far this seems to be working, but the bug appears sporadically and is hard to \
reproduce. <o:p></o:p></span></p> <p class="MsoNormal"><span \
style="font-size:11.0pt"><o:p> </o:p></span></p> <p class="MsoNormal"><span \
style="font-size:11.0pt">Please let me know if there is anything I can do to help \
track down this bug (debug settings to activate), or if you want more \
information. <o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt">Thanks,<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt">Geoffrey \
Blake<o:p></o:p></span></p> <p class="MsoNormal"><span \
style="font-size:11.0pt"><o:p> </o:p></span></p> <p class="MsoNormal"><span \
style="font-size:11.0pt;font-family:"Times New Roman";color:black">Staff \
Research Engineer<o:p></o:p></span></p> <p class="MsoNormal"><span \
style="font-size:11.0pt;font-family:"Times New Roman";color:black">5707 \
Southwest Pkwy<o:p></o:p></span></p> <p class="MsoNormal"><span \
style="font-size:11.0pt;font-family:"Times New Roman";color:black">Encino \
Trace<o:p></o:p></span></p> <p class="MsoNormal"><span \
style="font-size:11.0pt;font-family:"Times New Roman";color:black">Bld 1 \
Suite 100, Austin TX 78735<o:p></o:p></span></p> <p class="MsoNormal"><span \
style="font-size:11.0pt;font-family:"Times New Roman";color:black">T \
+(1) 512-329-7263</span><span style="font-size:11.0pt"><o:p></o:p></span></p> <p \
class="MsoNormal"><span style="font-size:11.0pt"><o:p> </o:p></span></p> </div>
IMPORTANT NOTICE: The contents of this email and any attachments are confidential and \
may also be privileged. If you are not the intended recipient, please notify the \
sender immediately and do not disclose the contents to any other person, use it for \
any purpose, or store or copy the information in any medium. Thank you.
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