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24bc5ea5c0
There's two patterns of taking the RCU read-lock and the
sig->stats_lock read-seqlock in do_task_stat() and
do_io_accounting(), with a different ordering:
# do_io_accounting():
guard(rcu)();
scoped_seqlock_read (&sig->stats_lock, ss_lock_irqsave) {
# do_task_stat():
scoped_seqlock_read (&sig->stats_lock, ss_lock_irqsave) {
...
rcu_read_lock();
The ordering is RCU-read+seqlock_read in the first
case, seqlock_read+RCU-read in the second case.
While technically these read locks can be taken in any order,
nevertheless it's good practice to use the more intrusive lock
on the inside (which is the IRQs-off section in this case),
and reduces head-scratching during review when done consistently,
so let's use the do_io_accounting() pattern in do_task_stat().
This will also reduce irqs-off latencies in do_task_stat() a tiny bit.
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Acked-by: Oleg Nesterov <oleg@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Christian Brauner <brauner@kernel.org>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Link: https://patch.msgid.link/aS6rwnaPbHFCdHp1@gmail.com
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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 reStructuredText 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.