Bug 1271192 - Incorrect handling of ERESTARTSYS could cause soft lockups
Incorrect handling of ERESTARTSYS could cause soft lockups
Product: Fedora
Classification: Fedora
Component: xorg-x11-drv-qxl (Show other bugs)
Unspecified Unspecified
unspecified Severity unspecified
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Assigned To: Frediano Ziglio
Fedora Extras Quality Assurance
Depends On:
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Reported: 2015-10-13 07:04 EDT by Frediano Ziglio
Modified: 2016-07-19 14:12 EDT (History)
8 users (show)

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Doc Type: Bug Fix
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Last Closed: 2016-07-19 14:12:14 EDT
Type: Bug
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Description Frediano Ziglio 2015-10-13 07:04:43 EDT
Description of problem:

Initial problem was reported about handling additional surfaces using QXL kernel driver and easy reproducible with KDE plasma.
I don't remember if I was reproducing with RHEL6/RHEL7 or Fedora 22 (surely I was using this as host).

I lost the reproduction environment and original bug.

Mainly I'm opening this bug to keep track of the issue.

The issue could happen even not using surfaces (but is much less probable). The problem is that when a signal is send to the program (which is likely to happen with X which receives a lot of SIGURG signals) the kernel driver goes into a tight loop on ERESTARTSYS. As Dave Airlie pointed out (https://lkml.org/lkml/2015/5/27/1038) this loop inside the kernel is done as QXL driver is not able to handle restarting the call correctly. However removing wait_for_io_cmd as suggested looks like can make the driver lose some command if sent too fast.

Would be good to have a PoC to make easier to reproduce this (even on primary surface creation and screen updates that is without surfaces) and fix the main issue.

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

How reproducible:

Enable surfaces (need to enable also in the driver).
Installe KDE plasma. Play with it for a while till you will see hangs and CPU usage going very high.

Steps to Reproduce:
1. patch driver to enable surfaces
2. install KDE plasma
3. play with interface

Actual results:

Hangs and slow downs

Expected results:

No hangs

Additional info:

See https://lkml.org/lkml/2015/5/27/1038 for proposed patch.
Comment 1 Frediano Ziglio 2015-10-13 07:05:42 EDT
Related issue is https://bugzilla.redhat.com/show_bug.cgi?id=1027831.
Comment 2 Fedora End Of Life 2016-07-19 14:12:14 EDT
Fedora 22 changed to end-of-life (EOL) status on 2016-07-19. Fedora 22 is
no longer maintained, which means that it will not receive any further
security or bug fix updates. As a result we are closing this bug.

If you can reproduce this bug against a currently maintained version of
Fedora please feel free to reopen this bug against that version. If you
are unable to reopen this bug, please file a new report against the
current release. If you experience problems, please add a comment to this

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