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

Tue Aug 6 06:33:44 UTC 2019

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):

7e865eba00a3df2dc8c4746173a8ca1c1c7f042e bcache: fix potential deadlock in cached_def_free()
80265d8dfd77792e133793cef44a21323aac2908 bcache: acquire bch_register_lock later in cached_dev_free()
ce4c3e19e5201424357a0c82176633b32a98d2ec bcache: Replace bch_read_string_list() by __sysfs_match_string()
ecb37ce9baac653cc09e2b631393dde3df82979f bcache: Move couple of functions to sysfs.c
04cbc21137bfa4d7b8771a5b14f3d6c9b2aee671 bcache: Move couple of string arrays to sysfs.c
5f2b18ec8e1643410a2369f06888951cdedea0bf bcache: Fix a compiler warning in bcache_device_init()
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
09a44ca2114737e0932257619c16a2b50c7807f1 bcache: use pr_info() to inform duplicated CACHE_SET_IO_DISABLE set
c4dc2497d50d9c6fb16aa0d07b6a14f3b2adb1e0 bcache: fix high CPU occupancy during journal
a728eacbbdd229d1d903e46261c57d5206f87a4a bcache: add journal statistic
616486ab52ab7f9739b066d958bdd20e65aefd74 bcache: fix writeback target calc on large devices
1f0ffa67349c56ea54c03ccfd1e073c990e7411e bcache: only set BCACHE_DEV_WB_RUNNING when cached device attached
eb8cbb6df38f6e5124a3d5f1f8a3dbf519537c60 bcache: improve bcache_reboot()
9951379b0ca88c95876ad9778b9099e19a95d566 bcache: never writeback a discard operation

[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 (that seems
to be a mainline bug - not fixed yet). We should spend more time trying
to reproduce this deadlock with a mainline kernel and post the patch to
the LKML for review / feedback.

However, considering that this patch seems to fix/prevent the specific
deadlock problem reported in this bug (tested on the affected platform),
it should be considered safe to apply it as it is for now, to prevent
potential hung task timeout conditions.

---
The following changes since commit face6017552c1e768188d512724720838be6d8c5:

  Revert "ovl: set I_CREATING on inode being created" (2019-08-06 01:13:14 -0400)

are available in the Git repository at:

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

for you to fetch changes up to 177e9156ee68080d5cc8f352a7ab86cb5caeaa85:

  UBUNTU: SAUCE: bcache: fix deadlock in bcache_allocator (2019-08-06 08:31:17 +0200)

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

Andy Shevchenko (3):
      bcache: Move couple of string arrays to sysfs.c
      bcache: Move couple of functions to sysfs.c
      bcache: Replace bch_read_string_list() by __sysfs_match_string()

Bart Van Assche (8):
      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
      bcache: Fix a compiler warning in bcache_device_init()

Coly Li (5):
      bcache: improve bcache_reboot()
      bcache: only set BCACHE_DEV_WB_RUNNING when cached device attached
      bcache: use pr_info() to inform duplicated CACHE_SET_IO_DISABLE set
      bcache: acquire bch_register_lock later in cached_dev_free()
      bcache: fix potential deadlock in cached_def_free()

Daniel Axtens (1):
      bcache: never writeback a discard operation

Michael Lyle (1):
      bcache: fix writeback target calc on large devices

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    | 10 ++++--
 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     | 57 +++++++++++++++-----------------
 drivers/md/bcache/sysfs.c     | 75 +++++++++++++++++++++++++++++++++++--------
 drivers/md/bcache/util.c      | 60 +++++++++-------------------------
 drivers/md/bcache/util.h      |  7 ++--
 drivers/md/bcache/writeback.c | 35 +++++++++++++++++---
 drivers/md/bcache/writeback.h | 12 ++++++-
 15 files changed, 215 insertions(+), 137 deletions(-)