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Subject[PATCH v12 0/2] blk-mq: Rework blk-mq timeout handling again
Hello Jens,

This patch series reworks blk-mq timeout handling by introducing a state
machine per request. Please consider this patch series for inclusion in the
upstream kernel.


Changes compared to v11:
- Reworked patch 1/2: instead of introducing CONFIG_ARCH_HAVE_CMPXCHG64, make
sure that cmpxchg64() is only defined if it can be used.

Changes compared to v10:
- In patch 1/2, added "default y if 64BIT" to the "config ARCH_HAVE_CMPXCHG64"
entry in arch/Kconfig. Left out the "select ARCH_HAVE_CMPXCHG64" statements
that became superfluous due to this change (alpha, arm64, powerpc and s390).
- Also in patch 1/2, only select ARCH_HAVE_CMPXCHG64 if X86_CMPXCHG64 has been
- In patch 2/2, moved blk_mq_change_rq_state() from blk-mq.h to blk-mq.c.
- Added a comment header above __blk_mq_requeue_request() and
- Documented the MQ_RQ_* state transitions in block/blk-mq.h.
- Left out the fourth argument of blk_mq_rq_set_deadline().

Changes compared to v9:
- Addressed multiple comments related to patch 1/2: added
CONFIG_ARCH_HAVE_CMPXCHG64 for riscv, modified
features/locking/cmpxchg64/arch-support.txt as requested and made the
order of the symbols in the arch/*/Kconfig alphabetical where possible.

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

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

Changes compared to v3 (see also
- 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 (
- Rebased and retested on top of kernel v4.16.

Changes compared to v1 (
- 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):
ARM: cmpxchg64: Only define cmpxchg64() if not using the Thumb
instruction set
blk-mq: Rework blk-mq timeout handling again

arch/arm/include/asm/cmpxchg.h | 4 +
block/blk-core.c | 6 --
block/blk-mq-debugfs.c | 1 -
block/blk-mq.c | 238 +++++++++++++++++++----------------------
block/blk-mq.h | 64 +++++------
block/blk-timeout.c | 133 +++++++++++++++--------
block/blk.h | 11 +-
include/linux/blkdev.h | 48 +++++----
8 files changed, 267 insertions(+), 238 deletions(-)


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