RHEL Engineering is moving the tracking of its product development work on RHEL 6 through RHEL 9 to Red Hat Jira (issues.redhat.com). If you're a Red Hat customer, please continue to file support cases via the Red Hat customer portal. If you're not, please head to the "RHEL project" in Red Hat Jira and file new tickets here. Individual Bugzilla bugs in the statuses "NEW", "ASSIGNED", and "POST" are being migrated throughout September 2023. Bugs of Red Hat partners with an assigned Engineering Partner Manager (EPM) are migrated in late September as per pre-agreed dates. Bugs against components "kernel", "kernel-rt", and "kpatch" are only migrated if still in "NEW" or "ASSIGNED". If you cannot log in to RH Jira, please consult article #7032570. That failing, please send an e-mail to the RH Jira admins at rh-issues@redhat.com to troubleshoot your issue as a user management inquiry. The email creates a ServiceNow ticket with Red Hat. Individual Bugzilla bugs that are migrated will be moved to status "CLOSED", resolution "MIGRATED", and set with "MigratedToJIRA" in "Keywords". The link to the successor Jira issue will be found under "Links", have a little "two-footprint" icon next to it, and direct you to the "RHEL project" in Red Hat Jira (issue links are of type "https://issues.redhat.com/browse/RHEL-XXXX", where "X" is a digit). This same link will be available in a blue banner at the top of the page informing you that that bug has been migrated.

Created attachment 558926 [details]
Test script used to reproduce error, and verify fix.

Description of problem:
pci_block_user_cfg_access was designed for the use case that a single
context, the IPR driver, temporarily delays user space accesses to the
config space via sysfs. This assumption became invalid by the time
pci_dev_reset was added as locking instance. Today, if you run two
loops in parallel that reset the same device via sysfs, you end up with
a kernel BUG as pci_block_user_cfg_access detect the broken assumption.

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


How reproducible:
Always

Steps to Reproduce:
1. login as root (to be able to write to sysfs of a device
2. run two shell scripts, each resetting the same pci device, with a 1 second
   delay between each reset.  Pick a device (extra nic card, for example) that
   host is not using.
3.
  
Actual results:
Host hangs within 5 seconds

Expected results:
The two threads can run indefinitely.


Additional info:
Backport of upstream commit fb51ccbf217c1c994607b6519c7d85250928553d
resolves this problem.
Note: straight cherry-pick/backport will break kabi since it renames
      pci_dev structure element, so must modify backport to maintain
      kabi.

This request was evaluated by Red Hat Product Management for inclusion
in a Red Hat Enterprise Linux maintenance release. Product Management has 
requested further review of this request by Red Hat Engineering, for potential
inclusion in a Red Hat Enterprise Linux Update release for currently deployed 
products. This request is not yet committed for inclusion in an Update release.

Test script to reproduce error, and verify (posted) fix:

!/bin/bash
for i in {1..1000}; do
  echo "[-- $i iteration -- $(date) -- ]"
  echo 1 > /sys/bus/pci/devices/0000\:05\:00.0/reset
  echo "sleep 1 secs"
  sleep 1
done

Patch(es) available on kernel-2.6.32-238.el6

Good job!
The 220.el6 kernel hung before the second iteration of reproducer,
the 238.el6 kernel survived 744+ iterations till now.
After the 1000th iteration I'll set this BZ to VERIFIED state.

Since the problem described in this bug report should be
resolved in a recent advisory, it has been closed with a
resolution of ERRATA.

For information on the advisory, and where to find the updated
files, follow the link below.

If the solution does not work for you, open a new bug report.

http://rhn.redhat.com/errata/RHSA-2012-0862.html