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Description of problem:

The VDO code that implements the sysfs nodes that read statistics (i.e. /sys/kvdo/vdo0/statistics/*) all hold a spin lock and call a method that gathers the statistics.  This gathering method always sends a message to another thread and waits for the thread to send back a reply, and the waiting always sleeps.  But sleeping is not allowed while holding a spin lock.


Version-Release number of selected component (if applicable):
6.1.0.154

How reproducible:
always takes spin lock and sleeps, but it takes multiple simultaneous calls to cause very bad effects.

Steps to Reproduce:

Unsure - this was discovered in the source code code

Actual results:


Expected results:


Additional info:

It is possible that throwing a lot of processes doing "/sys/kvdo/vdo0/statistics/*" simultaneously would show a problem.  But it is most reasonable to do the standard sanity testing after this is fixed.

The simplest fix is to take out the spin lock and replace it with a mutex.

The bug was merged back to version 6.1.1.40.

Sanity testing found no regressions on:
RHEL-7.6-20180626.0
kernel-3.10.0-915.el7
kmod-vdo-6.1.1.99-1.el7
vdo-6.1.1.99-2.el7

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.

https://access.redhat.com/errata/RHBA-2018:3094