[PATCH 0/2][SRC][BIONIC] fix zram kernel hard lockup (LP: #1799497)

[Colin King]

From: Colin Ian King <colin.king at canonical.com>

BugLink: https://bugs.launchpad.net/bugs/1799497

== SRU Justification [BIONIC ONLY] ==

When using zram (as installed and configured with the zram-config package)
systems can lockup after about a week of use.  This occurs because of
a hang in a lock in zram.

== Test Case ==

Run stress-ng --brk 0 --stack 0 in a Bionic amd64 server VM with 1GM of
memory, 16 CPU threads and zram-config installed.  Without the fix the
kernel will hang in a spinlock after 1-2 hours of run time. With the fix,
the hang does not occur.  Testing shows that with the fix, 5 x 16 CPU hours
of stress testing with stress-ng works fine without the lockup occurring.

== The fix ==

Upstream commit c4d6c4cc7bfd ("zram: correct flag name of ZRAM_ACCESS") as
a prerequisite followed by a minor line wiggle backport of the fix with 
commit 3c9959e02547 ("zram: fix lockdep warning of free block handling").

== Regression Potential ==

This touches the zram locking, so the core zram driver is affected. However
the fixes are backports from 5.0, so the fixes have had a fair amount of
testing in later kernels.

Minchan Kim (2):
  zram: fix lockdep warning of free block handling
  zram: correct flag name of ZRAM_ACCESS

 drivers/block/zram/zram_drv.c | 58 +++++++++++++++++++++++--------------------
 drivers/block/zram/zram_drv.h |  8 +++---
 2 files changed, 35 insertions(+), 31 deletions(-)

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2.7.4