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82a4f9ff8b
When mod_delayed_work() is concurrently executed, there a potential
live lock scenario due to pool->lock contention.
Lets say both CPU#0 and CPU#4 calls mod_delayed_work() on the same
work item with 0 delay on a bounded workqueue. This workitem has
run on CPU#4 previously. CPU#0 wins the work item PENDING bit race
and proceeds to queueing. As this work has previously run on CPU#4,
it tries to acquire the corresponding pool->lock to check if it is
still running there. In the meantime, CPU#4 loops in
try_to_grab_pending() for the workitem to be linked with a pwq so
that it can steal it from pwq->pool->worklist. The CPU#4 essentially
acquires and releases the pool->lock in a busy loop and CPU#0 may
never gets this lock.
---------------- --------------------
CPU#0 CPU#4
--------------- --------------------
blk_run_queue_async()
mod_delayed_work_on() queue_unplugged()
--> try_to_grab_pending() returns blk_run_queue_async()
0 indicating PENDING bit is set
now.
__queue_delayed_work() mod_delayed_work_on()
__queue_work() try_to_grab_pending()
{
--> waiting for the CPU#4's acquire pool->lock()
pool->lock release pool->lock()
}
Change-Id: I9aeab111f55a19478a9d045c8e3576bce3b7a7c5
Signed-off-by: Pavankumar Kondeti <pkondeti@codeaurora.org>
Signed-off-by: Elliot Berman <eberman@codeaurora.org>
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| abi_gki_aarch64.xml | ||
| abi_gki_aarch64_cf045d8.xml | ||
| build.config.cuttlefish.aarch64 | ||
| build.config.cuttlefish.x86_64 | ||
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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.