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

Wed Aug 7 09:20:58 UTC 2019

I'll send a new pull request with the additional changes from the last
reviews.

-Andrea

On Tue, Aug 06, 2019 at 08:33:44AM +0200, Andrea Righi wrote:
> 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(-)