[PATCH v9 0/2] blk-mq: Rework blk-mq timeout handling again

[Bart Van Assche]

Hello Jens,

This is the ninth incarnation of the blk-mq timeout handling rework. All
previously posted comments have been addressed. Please consider this patch
series for inclusion in the upstream kernel.

Bart.

Changes compared to v8:
- Split into two patches.
- Moved the spin_lock_init() call from blk_mq_rq_ctx_init() into
  blk_mq_init_request().
- Fixed the deadline set by blk_add_timer().
- Surrounded the das_lock member with #ifndef CONFIG_ARCH_HAVE_CMPXCHG64 /
  #endif.

Changes compared to v7:
- Fixed the generation number mechanism. Note: with this patch applied the
  behavior of the block layer does not depend on the generation number.
- Added more 32-bit architectures to the list of architectures on which
  cmpxchg64() should not be used.

Changes compared to v6:
- Used a union instead of bit manipulations to store multiple values into
  a single 64-bit field.
- Reduced the size of the timeout field from 64 to 32 bits.
- Made sure that the block layer still builds with this patch applied
  for the sh and mips architectures.
- Fixed two sparse warnings that were introduced by this patch in the
  WRITE_ONCE() calls.

Changes compared to v5:
- Restored the synchronize_rcu() call between marking a request for timeout
  handling and the actual timeout handling to avoid that timeout handling
  starts while .queue_rq() is still in progress if the timeout is very short.
- Only use cmpxchg() if another context could attempt to change the request
  state concurrently. Use WRITE_ONCE() otherwise.

Changes compared to v4:
- Addressed multiple review comments from Christoph. The most important are
  that atomic_long_cmpxchg() has been changed into cmpxchg() and also that
  there is now a nice and clean split between the legacy and blk-mq versions
  of blk_add_timer().
- Changed the patch name and modified the patch description because there is
  disagreement about whether or not the v4.16 blk-mq core can complete a
  single request twice. Kept the "Cc: stable" tag because of
  https://bugzilla.kernel.org/show_bug.cgi?id=199077.

Changes compared to v3 (see also https://www.mail-archive.com/linux-block@xxxxxxxxxxxxxxx/msg20073.html):
- Removed the spinlock again that was introduced to protect the request state.
  v4 uses atomic_long_cmpxchg() instead.
- Split __deadline into two variables - one for the legacy block layer and one
  for blk-mq.

Changes compared to v2 (https://www.mail-archive.com/linux-block@xxxxxxxxxxxxxxx/msg18338.html):
- Rebased and retested on top of kernel v4.16.

Changes compared to v1 (https://www.mail-archive.com/linux-block@xxxxxxxxxxxxxxx/msg18089.html):
- Removed the gstate and aborted_gstate members of struct request and used
  the __deadline member to encode both the generation and state information.
Bart Van Assche (2):
  arch/*: Add CONFIG_ARCH_HAVE_CMPXCHG64
  blk-mq: Rework blk-mq timeout handling again

 .../features/locking/cmpxchg64/arch-support.txt    |  31 ++++
 arch/Kconfig                                       |   3 +
 arch/alpha/Kconfig                                 |   1 +
 arch/arm/Kconfig                                   |   1 +
 arch/arm64/Kconfig                                 |   1 +
 arch/ia64/Kconfig                                  |   1 +
 arch/m68k/Kconfig                                  |   1 +
 arch/mips/Kconfig                                  |   1 +
 arch/parisc/Kconfig                                |   1 +
 arch/powerpc/Kconfig                               |   1 +
 arch/s390/Kconfig                                  |   1 +
 arch/sparc/Kconfig                                 |   1 +
 arch/x86/Kconfig                                   |   1 +
 arch/xtensa/Kconfig                                |   1 +
 block/blk-core.c                                   |   6 -
 block/blk-mq-debugfs.c                             |   1 -
 block/blk-mq.c                                     | 183 ++++++---------------
 block/blk-mq.h                                     | 117 ++++++++++---
 block/blk-timeout.c                                |  95 ++++++-----
 block/blk.h                                        |  14 +-
 include/linux/blkdev.h                             |  47 +++---
 21 files changed, 276 insertions(+), 233 deletions(-)
 create mode 100644 Documentation/features/locking/cmpxchg64/arch-support.txt

-- 
2.16.3