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Bug 157707 - Oops in proc_pid_stat() when dereferencing ->real_parent in a dead task.
Summary: Oops in proc_pid_stat() when dereferencing ->real_parent in a dead task.
Alias: None
Product: Red Hat Enterprise Linux 4
Classification: Red Hat
Component: kernel
Version: 4.0
Hardware: All
OS: Linux
Target Milestone: ---
: ---
Assignee: Ingo Molnar
QA Contact: Brian Brock
Depends On:
TreeView+ depends on / blocked
Reported: 2005-05-13 21:59 UTC by Michael Gaughen
Modified: 2007-11-30 22:07 UTC (History)
2 users (show)

Fixed In Version: 2.6.9-11.EL
Doc Type: Bug Fix
Doc Text:
Clone Of:
Last Closed: 2005-09-15 22:43:11 UTC
Target Upstream Version:

Attachments (Terms of Use)
Proposed kernel patch to fix the oops in proc_pid_stat(). (deleted)
2005-05-13 22:01 UTC, Michael Gaughen
no flags Details | Diff

Description Michael Gaughen 2005-05-13 21:59:10 UTC
From Bugzilla Helper:
User-Agent: Mozilla/5.0 (X11; U; Linux x86_64; en-US; rv:1.7.2) Gecko/20040803

Description of problem:
In certain cases, proc_pid_stat() can dereference an invalid ->real_parent if the task is in the TASK_DEAD state.  The same problem had existed in task_state(), but was fixed by calling pid_alive() to see if the task was alive or not before dereferencing any of the task's pointer fields.  A similar fix should go into proc_pid_stat().

This same problem was also reported to lkml here:

and was fixed in the 2.6.11 kernel.

Version-Release number of selected component (if applicable):

How reproducible:

Steps to Reproduce:
1. Run any program that will read /proc task entries (eg. top, ps)
2. Start various processes that exit (or can be killed) while top, ps, etc. is
   running.  In some cases, proc_pid_stat() will deal with a task that is marked 
   TASK_DEAD, and dereferencing ->real_parent will cause an oops.

Additional info:

Comment 1 Michael Gaughen 2005-05-13 22:01:45 UTC
Created attachment 114363 [details]
Proposed kernel patch to fix the oops in proc_pid_stat().

Comment 2 Ingo Molnar 2005-09-15 22:43:11 UTC
this bug should be fixed in the RHEL4-U1 kernel.

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