[SRU][X][PULL v2] bcache: fix hung task timeout in bch_bucket_alloc()

[Andrea Righi]

BugLink: https://bugs.launchpad.net/bugs/1784665

[Impact]

bcache_allocator can call the following:

 bch_allocator_thread()
  -> bch_prio_write()
     -> bch_bucket_alloc()
        -> wait on &ca->set->bucket_wait

But the wake up event on bucket_wait is supposed to come from
bch_allocator_thread() itself causing a deadlock.

[Test Case]

This is a simple script that can easily trigger the deadlock condition:
https://launchpadlibrarian.net/381282009/bcache-basic-repro.sh

A better test case has been also provided in LP: #1796292:
https://bugs.launchpad.net/curtin/+bug/1796292/+attachment/5280353/+files/curtin-nvme.sh

[Fix]

Fix by making the call to bch_prio_write() non-blocking, so that
bch_allocator_thread() never waits on itself. Moreover, make sure to
wake up the garbage collector thread when bch_prio_write() is failing to
allocate buckets to increase the chance of freeing up more buckets.

In addition to that it would be safer to also import other upstream
bcache fixes (all clean cherry picks):

ecb37ce9baac653cc09e2b631393dde3df82979f bcache: Move couple of functions to sysfs.c
20d3a518713e394efa5a899c84574b4b79ec5098 bcache: Reduce the number of sparse complaints about lock imbalances
42361469ae84c851e40cb1f94c8c9a14cdd94039 bcache: Suppress more warnings about set-but-not-used variables
f0d3814090ac77de94c42b7124c37ece23629197 bcache: Remove an unused variable
47344e330eabc1515cbe6061eb337100a3ab6d37 bcache: Fix kernel-doc warnings
9dfbdec7b7fea1ff1b7b5d5d12980dbc7dca46c7 bcache: Annotate switch fall-through
4a4e443835a43a79113cc237c472c0d268eb1e1c bcache: Add __printf annotation to __bch_check_keys()
fd01991d5c20098c5c1ffc4dca6c821cc60a2f74 bcache: Fix indentation
ca71df31661a0518ed58a1a59cf1993962153ebb bcache: fix using of loop variable in memory shrink
f3641c3abd1da978ee969b0203b71b86ec1bfa93 bcache: fix error return value in memory shrink
688892b3bc05e25da94866e32210e5f503f16f69 bcache: fix incorrect sysfs output value of strip size
c4dc2497d50d9c6fb16aa0d07b6a14f3b2adb1e0 bcache: fix high CPU occupancy during journal
a728eacbbdd229d1d903e46261c57d5206f87a4a bcache: add journal statistic
eb8cbb6df38f6e5124a3d5f1f8a3dbf519537c60 bcache: improve bcache_reboot()

[Regression Potential]

The upstream fixes are all clean cherry picks from stable (most of them
are small cleanups), so regression potential is minimal.

The only special patch is "UBUNTU: SAUCE: bcache: fix deadlock in
bcache_allocator" that is addressing the main deadlock bug. Even if this
patch is not yet applied upstream (posted to the LKML), it seems to
reliably fix/prevent the specific deadlock problem reported in this bug,
so it should be considered safe to apply it as it is for now, to prevent
potential hung task timeout conditions.

Changes in v2:
 - fix potential buckets leak in "UBUNTU: SAUCE: bcache: fix deadlock in
   bcache_allocator"

----------------------------------------------------------------
The following changes since commit 4a916e0ee66c44ecdf473dc96a5ff2e4ad4ae196:

  floppy: fix out-of-bounds read in copy_buffer (2019-08-07 00:54:59 -0400)

are available in the Git repository at:

  git://git.launchpad.net/~arighi/+git/xenial-linux bcache-fix-v2

for you to fetch changes up to 4f40d1b13ac6288a8a842c1fa6fcd49ccc8de0b9:

  UBUNTU: SAUCE: bcache: fix deadlock in bcache_allocator (2019-08-07 14:19:12 +0200)

----------------------------------------------------------------
Andrea Righi (1):
      UBUNTU: SAUCE: bcache: fix deadlock in bcache_allocator

Andy Shevchenko (1):
      bcache: Move couple of functions to sysfs.c

Bart Van Assche (7):
      bcache: Fix indentation
      bcache: Add __printf annotation to __bch_check_keys()
      bcache: Annotate switch fall-through
      bcache: Fix kernel-doc warnings
      bcache: Remove an unused variable
      bcache: Suppress more warnings about set-but-not-used variables
      bcache: Reduce the number of sparse complaints about lock imbalances

Coly Li (1):
      bcache: improve bcache_reboot()

Tang Junhui (5):
      bcache: add journal statistic
      bcache: fix high CPU occupancy during journal
      bcache: fix incorrect sysfs output value of strip size
      bcache: fix error return value in memory shrink
      bcache: fix using of loop variable in memory shrink

 drivers/md/bcache/alloc.c     |  5 +++-
 drivers/md/bcache/bcache.h    |  8 +++++-
 drivers/md/bcache/bset.c      |  4 +--
 drivers/md/bcache/bset.h      |  5 ++--
 drivers/md/bcache/btree.c     | 15 ++++++-----
 drivers/md/bcache/closure.c   |  8 +++---
 drivers/md/bcache/extents.c   |  2 --
 drivers/md/bcache/journal.c   | 56 ++++++++++++++++++++++++++++------------
 drivers/md/bcache/request.c   |  1 +
 drivers/md/bcache/super.c     | 39 ++++++++++++++++++++++------
 drivers/md/bcache/sysfs.c     | 52 ++++++++++++++++++++++++++++++++++++-
 drivers/md/bcache/util.c      | 60 +++++++++++--------------------------------
 drivers/md/bcache/util.h      |  7 ++---
 drivers/md/bcache/writeback.h |  2 +-
 14 files changed, 170 insertions(+), 94 deletions(-)