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de6c5e3a45
[ Upstream commit 42c306ed723321af4003b2a41bb73728cab54f85 ]
Consider the following scenario:
Process 1 Process 2 Process 3 Process 4
(BIC1) (BIC2) (BIC3) (BIC4)
Λ | | |
\-------------\ \-------------\ \--------------\|
V V V
bfqq1--------->bfqq2---------->bfqq3----------->bfqq4
ref 0 1 2 4
If Process 1 issue a new IO and bfqq2 is found, and then bfq_init_rq()
decide to spilt bfqq2 by bfq_split_bfqq(). Howerver, procress reference
of bfqq2 is 1 and bfq_split_bfqq() just clear the coop flag, which will
break the merge chain.
Expected result: caller will allocate a new bfqq for BIC1
Process 1 Process 2 Process 3 Process 4
(BIC1) (BIC2) (BIC3) (BIC4)
| | |
\-------------\ \--------------\|
V V
bfqq1--------->bfqq2---------->bfqq3----------->bfqq4
ref 0 0 1 3
Since the condition is only used for the last bfqq4 when the previous
bfqq2 and bfqq3 are already splited. Fix the problem by checking if
bfqq is the last one in the merge chain as well.
Fixes: 36eca89483 ("block, bfq: add Early Queue Merge (EQM)")
Signed-off-by: Yu Kuai <yukuai3@huawei.com>
Link: https://lore.kernel.org/r/20240902130329.3787024-4-yukuai1@huaweicloud.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Sasha Levin <sashal@kernel.org>
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.