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Filename Latest commit message Latest commit date
Sebastian Andrzej Siewior 9d7c249a1e serial: 8250: drop the printk from serial8250_interrupt()
The printk() in serial8250_interrupt() was once hidden behind a debug
macro in commit f4f653e987 ("serial: 8250, disable "too much work"
messages") and reverted back in commit 12de375ec4 ("Revert "serial:
8250, disable "too much work" messages"").

This was introduced first in 0.99.13k with the "serial" driver itself
(and called pass_number with a limit of 64 and no print). In 1.1.13 it
was renamed to pass_counter and the printk was behind #if 0. In 1.1.94
the limit of 64 was increased to 256 and hidden behind
RS_ISR_PASS_LIMIT. With this change the #if 0 turned into #if 1. It
slowly become what we have today with a loop limit of 512.

Usually, that printk isn't hit. However on KVM with a busy UART and
overloaded host it might happen. It is also likely with threaded
interrupts and a task which preempts the interrupt handler.

If the UART has (legitimate) work to do and we break out of the loop,
nothing changes: the interrupt is most likely already pending in the
interrupt controller and we end up in the handler anyway. This printk is
hardly helping.

Older kernels also had a comment saying that a bad configuration might
lead to this but I don't see how that should happen because a wrongly
configured interrupt number would let the handler leave "early" with
IRQ_NONE and the spurious detected will handle that (weill since 2.6.11,
before that we had no spurious detector). In that case, we would never
loop that often here.

This loop looks like an optimisation in order to pull the bytes from the
FIFO which were received while we were already here instead of waiting
for the interrupt. This might have been a good idea while the CPUs were
slow and FIFOs small.
There are other serial driver in tree, like the amba-pl*, which also
have this kind of a loop but without the printk (and were based on this
driver).

Remove the printk which might trigger in otherwise valid situtations.

Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
2018-09-18 16:07:23 +02:00
arch Merge branch 'x86-urgent-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip 2018-09-15 08:02:46 -10:00
block blk-cgroup: increase number of supported policies 2018-09-11 10:59:53 -06:00
certs
crypto
Documentation Merge 4.19-rc4 into tty-next 2018-09-18 14:28:54 +02:00
drivers serial: 8250: drop the printk from serial8250_interrupt() 2018-09-18 16:07:23 +02:00
firmware
fs fixes for four CIFS/SMB3 potential pointer overflow issues, one minor build fix, and a build warning cleanup 2018-09-14 19:33:42 -10:00
include Merge 4.19-rc4 into tty-next 2018-09-18 14:28:54 +02:00
init
ipc ipc/shm: properly return EIDRM in shm_lock() 2018-09-04 16:45:02 -07:00
kernel Merge branch 'sched-urgent-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip 2018-09-15 08:00:37 -10:00
lib lib/Kconfig.debug: fix three typos in help text 2018-09-04 16:45:02 -07:00
LICENSES
mm overlayfs fixes for 4.19-rc4 2018-09-13 19:21:40 -10:00
net tipc: check return value of __tipc_dump_start() 2018-09-12 13:15:04 -07:00
samples
scripts Kbuild fixes for v4.19 2018-09-09 05:42:11 -07:00
security Revert "x86/mm/legacy: Populate the user page-table with user pgd's" 2018-09-14 17:08:45 +02:00
sound ALSA: hda: Fix several mismatch for register mask and value 2018-09-03 23:47:40 +02:00
tools Merge branch 'perf-urgent-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip 2018-09-15 06:44:32 -10:00
usr
virt KVM: Remove obsolete kvm_unmap_hva notifier backend 2018-09-07 15:06:02 +02:00
.clang-format
.cocciconfig
.get_maintainer.ignore
.gitattributes
.gitignore
.mailmap
COPYING
CREDITS
Kbuild
Kconfig
MAINTAINERS Merge 4.19-rc4 into tty-next 2018-09-18 14:28:54 +02:00
Makefile Linux 4.19-rc4 2018-09-16 11:52:37 -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.
See Documentation/00-INDEX for a list of what is contained in each file.

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.