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Paolo Valente 7ea96eefb0 block, bfq: avoid circular stable merges
BFQ may merge a new bfq_queue, stably, with the last bfq_queue
created. In particular, BFQ first waits a little bit for some I/O to
flow inside the new queue, say Q2, if this is needed to understand
whether it is better or worse to merge Q2 with the last queue created,
say Q1. This delayed stable merge is performed by assigning
bic->stable_merge_bfqq = Q1, for the bic associated with Q1.

Yet, while waiting for some I/O to flow in Q2, a non-stable queue
merge of Q2 with Q1 may happen, causing the bic previously associated
with Q2 to be associated with exactly Q1 (bic->bfqq = Q1). After that,
Q2 and Q1 may happen to be split, and, in the split, Q1 may happen to
be recycled as a non-shared bfq_queue. In that case, Q1 may then
happen to undergo a stable merge with the bfq_queue pointed by
bic->stable_merge_bfqq. Yet bic->stable_merge_bfqq still points to
Q1. So Q1 would be merged with itself.

This commit fixes this error by intercepting this situation, and
canceling the schedule of the stable merge.

Fixes: 430a67f9d6 ("block, bfq: merge bursts of newly-created queues")
Signed-off-by: Pietro Pedroni <pedroni.pietro.96@gmail.com>
Signed-off-by: Paolo Valente <paolo.valente@linaro.org>
Link: https://lore.kernel.org/r/20210512094352.85545-2-paolo.valente@linaro.org
Signed-off-by: Jens Axboe <axboe@kernel.dk>
2021-05-12 07:39:23 -06:00
arch The x86 MM changes in this cycle were: 2021-04-29 11:41:43 -07:00
block block, bfq: avoid circular stable merges 2021-05-12 07:39:23 -06:00
certs certs: add 'x509_revocation_list' to gitignore 2021-04-26 10:48:07 -07:00
crypto for-5.13/drivers-2021-04-27 2021-04-28 14:39:37 -07:00
Documentation - removed get_fs/set_fs 2021-04-29 11:28:08 -07:00
drivers nvmet: remove unsupported command noise 2021-05-04 09:39:26 +02:00
fs block: reexpand iov_iter after read/write 2021-05-06 09:24:03 -06:00
include kyber: fix out of bounds access when preempted 2021-05-11 08:12:14 -06:00
init Merge branch 'for-5.13' of git://git.kernel.org/pub/scm/linux/kernel/git/tj/cgroup 2021-04-27 18:47:42 -07:00
ipc fs: make helpers idmap mount aware 2021-01-24 14:27:20 +01:00
kernel The x86 MM changes in this cycle were: 2021-04-29 11:41:43 -07:00
lib - removed get_fs/set_fs 2021-04-29 11:28:08 -07:00
LICENSES LICENSES: Add the CC-BY-4.0 license 2020-12-08 10:33:27 -07:00
mm \n 2021-04-29 11:06:13 -07:00
net Scheduler updates for this cycle are: 2021-04-28 13:33:57 -07:00
samples vfio/mdev: Correct the function signatures for the mdev_type_attributes 2021-04-12 10:36:00 -06:00
scripts Devicetree updates for v5.13: 2021-04-28 15:50:24 -07:00
security Devicetree updates for v5.13: 2021-04-28 15:50:24 -07:00
sound - Core Frameworks 2021-04-28 15:59:13 -07:00
tools Perf events changes in this cycle were: 2021-04-28 13:03:44 -07:00
usr Kbuild updates for v5.12 2021-02-25 10:17:31 -08:00
virt KVM: x86/mmu: Consider the hva in mmu_notifier retry 2021-02-22 13:16:53 -05:00
.clang-format cxl for 5.12 2021-02-24 09:38:36 -08:00
.cocciconfig
.get_maintainer.ignore
.gitattributes .gitattributes: use 'dts' diff driver for dts files 2019-12-04 19:44:11 -08:00
.gitignore clang-lto series for v5.12-rc1 2021-02-23 09:28:51 -08:00
.mailmap It's been a relatively busy cycle in docsland, though more than usually 2021-04-26 13:22:43 -07:00
COPYING COPYING: state that all contributions really are covered by this file 2020-02-10 13:32:20 -08:00
CREDITS - Core Frameworks 2021-04-28 15:59:13 -07:00
Kbuild kbuild: rename hostprogs-y/always to hostprogs/always-y 2020-02-04 01:53:07 +09:00
Kconfig kbuild: ensure full rebuild when the compiler is updated 2020-05-12 13:28:33 +09:00
MAINTAINERS Here's a collection of largely clk driver updates for the merge window. The 2021-04-28 17:13:56 -07:00
Makefile CFI on arm64 series for v5.13-rc1 2021-04-27 10:16:46 -07:00
README

Linux kernel
============

There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.

In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``.  The formatted documentation can also be read online at:

    https://www.kernel.org/doc/html/latest/

There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.

Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.