Public bug reported:
< NOTE: patches will be sent to kernel-team mailing list. >
[Impact]
* fscache issue where jobs get hung when fscache disk is full.
* trivial upstream fix; already applied in X/D, required in B/C:
commit c5a94f434c82 ("fscache: fix race between enablement and
dropping of object").
[Test Case]
* Test kernel verified / regression-tested by reporter.
* Apparently there's no simple test case,
but these are the conditions to hit the problem:
1) The active dataset size is equal to the cache disk size.
The application reads the data over and over again.
2) Disk is near full (90%+)
3) cachefilesd in userspace is trying to cull the old objects
while new objects are being looked up.
4) new cachefiles are created and some fail with no disk space.
5) race in dropping object state machine and
deferred lookup state machine causes the hang.
6) HUNG in fscache_wait_for_deferred_lookup for
clear bit FSCACHE_COOKIE_LOOKING_UP cookie->flags.
[Regression Potential]
* Low; contained in fscache; no further fixes applied upstream.
* This patch is applied in a stable tree (linux-4.4.y).
[Original Description]
An user reported an fscache issue where jobs get hung when the fscache
disk is full.
After investigation, it's been found to be an issue already reported/fixed
upstream,
by commit c5a94f434c82 ("fscache: fix race between enablement and dropping of
object").
This patch is required in Bionic and Cosmic, and it's applied in Xenial
(via stable) and Disco.
Apparently there's no simple test case, but these are the conditions to
hit the problem:
1) The active dataset size is equal to the cache disk size.
The application reads the data over and over again.
2) Disk is near full (90%+)
3) cachefilesd in userspace is trying to cull the old objects
while new objects are being looked up.
4) new cachefiles are created and some fail with no disk space.
5) race in dropping object state machine and
deferred lookup state machine causes the hang.
6) HUNG in fscache_wait_for_deferred_lookup for
clear bit FSCACHE_COOKIE_LOOKING_UP cookie->flags.
** Affects: linux (Ubuntu)
Importance: Undecided
Status: New
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https://bugs.launchpad.net/bugs/1821395
Title:
fscache: jobs might hang when fscache disk is full
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