This bug was fixed in the package linux - 4.4.0-135.161
---------------
linux (4.4.0-135.161) xenial; urgency=medium
* linux: 4.4.0-135.161 -proposed tracker (LP: #1788766)
* [Regression] APM Merlin boards fail to recover link after interface down/up
(LP: #1785739)
- net: phylib: fix interrupts re-enablement in phy_start
- net: phy: fix phy_start to consider PHY_IGNORE_INTERRUPT
* qeth: don't clobber buffer on async TX completion (LP: #1786057)
- s390/qeth: don't clobber buffer on async TX completion
* nvme: avoid cqe corruption (LP: #1788035)
- nvme: avoid cqe corruption when update at the same time as read
* CacheFiles: Error: Overlong wait for old active object to go away.
(LP: #1776254)
- cachefiles: Fix missing clear of the CACHEFILES_OBJECT_ACTIVE flag
- cachefiles: Wait rather than BUG'ing on "Unexpected object collision"
* fscache cookie refcount updated incorrectly during fscache object allocation
(LP: #1776277) // fscache cookie refcount updated incorrectly during fscache
object allocation (LP: #1776277)
- fscache: Fix reference overput in fscache_attach_object() error handling
* FS-Cache: Assertion failed: FS-Cache: 6 == 5 is false (LP: #1774336)
- Revert "UBUNTU: SAUCE: CacheFiles: fix a read_waiter/read_copier race"
- fscache: Allow cancelled operations to be enqueued
- cachefiles: Fix refcounting bug in backing-file read monitoring
* linux-cloud-tools-common: Ensure hv-kvp-daemon.service starts before
walinuxagent.service (LP: #1739107)
- [Debian] hyper-v -- Ensure that hv-kvp-daemon.service starts before
walinuxagent.service
-- Khalid Elmously <[email protected]> Sun, 26 Aug 2018
23:56:50 -0400
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https://bugs.launchpad.net/bugs/1776254
Title:
CacheFiles: Error: Overlong wait for old active object to go away.
Status in linux package in Ubuntu:
Fix Released
Status in linux source package in Trusty:
Fix Released
Status in linux source package in Xenial:
Fix Released
Status in linux source package in Bionic:
Fix Released
Bug description:
== SRU Justification ==
[Impact]
Oops during heavy NFS + FSCache + Cachefiles use:
CacheFiles: Error: Overlong wait for old active object to go away.
BUG: unable to handle kernel NULL pointer dereference at 0000000000000002
CacheFiles: Error: Object already active
kernel BUG at fs/cachefiles/namei.c:163!
[Cause]
In a heavily loaded system with big files being read and truncated,
an fscache object for a cookie is being dropped and a new object being
looked.
The new object being looked for has to wait for the old object to go away
before the
new object is moved to active state.
[Fix]
Clear the flag 'CACHEFILES_OBJECT_ACTIVE' for the new object when
retrying
the object lookup.
Remove the BUG() for the case where the old object is still being dropped
and convert to WARN()
[Testcase]
A user has run ~100 hours of NFS stress tests and not seen this bug recur.
[Regression Potential]
- Limited to fscache/cachefiles.
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